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Feedback loops How nature gets itrhythm- Anje-Margriet

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Feedback loops: How nature gets its rhythms – Anje-Margriet Neutel

While feedback loops are a bummer at band practice, they are essential in nature. What does natures feedback look like, and how does it build the resilience of our world? Anje-Margriet Neutel describes some common positive and negative feedback loops, examining how an ecosystems many loops come together to make its trademark sound.

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Anje-Margriet Neutel, Antonio Bodini, Eric Berlow

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The music in this lesson was composed byRoss Allchurch.

What isfeedback? It is a process that is the result of mutual causal interaction: X affects Y and Y affects X. The mutual causal interaction creates a circuit of effects, so that any change in X, causing a change in Y, in turn causes another change in X, and so on a feedback loop. Feedbacks are either positive or negative. The word positive here means that they reinforce a disturbance, an initial kick. Positive feedbacks are amplifiers. They are forces of divergence, they can make a system expand, but also spin out of control. They can cause development or degradation. Negative feedbacks on the other hand are forces of convergence, of conservation. The word negative here means that they counteract a disturbance. Negative feedbacks can restore the balance. They pull the system back.

Feedbacks affect the way every single variable, every population in an ecosystem for example, responds to both internal and external perturbations. Feedbacks determine how each part of a system responds to such changes, and all the feedbacks together determine the resilience of the whole system. It is only at the system level that you can really speak about stability. Just like when you make music, a single tone can sound very different in isolation, compared to when it is played in combination with other tones. Or, when you play on your own, your sound is very different from when you play in an ensemble – when you make music together the instruments influence each other.

That is what happens with feedbacks in an ecosystem as well, it is all about the combination of feedbacks.

Learn more abouthow feedbacks work, aboutpositive feedbacks in natural systems, andthe relation between feedback and system stability.

Natural communities do not consist of simple food chains, they are complex networks of interactions. But how do we get our heads around the multitude of feedbacks in an ecological network?

What will happen to a food web when we hunt big predators to extinction? How vulnerable is our food production when honeybees are under threat? And how important is dead organic matter for the stability of an ecosystem? All these are questions about ecological feedbacks. When there is a perturbation – disturbance – to one species in an ecosystem (for example increased mortality of a species due to pollution, reduced fecundity because of habitat fragmentation, introduction of an exotic species, and so forth), all the species in the food web may show some response, because they are connected. How much they will change and in what direction, depends on the feedback structure of the entire system.

To learn more about chains of interactions in complex ecological networks, watch theTED-Ed Lessons about the extinction of big predatorspollination by honeybees, anddetritus.

Measuring the feedbacks in real systems

It is only recently, mainly because of increased computer power, that ecologists have started to describe and quantify the feedbacks in observed ecological networks and identify patterns, taking steps in understanding the behaviour and structure of real complex ecosystems.

Here are some examples of papers by the educators:on making predictions for ecosystem managementon the patterns of feedbacks causing stability,andon ecosystem complexity and stability.

Basic concept and examples in various realms of life:

Maruyama, M. (1963) The second cybernetics: Deviation-amplifying mutual causal processes.Am. Sci. 51, 164-179.

Mathematical biology textbook on positive feedback:

DeAngelis, D.L., Post, W.M. & Travis, C.C. (1986)Positive Feedback in Natural Systems. Springer-Verlag, Berlin, pp. 221-244.

Mathematical background on the relation between feedback and stability in biological systems:

Levins, R. (1974) The qualitative analysis of partially specified systemsAnn. N Y Acad. Sci.,231, 123-138.

Papers on food webs, feedbacks and stability by the educators:

Bodini A.(1998) Representing ecosystem structure through signed digraphs. Model reconstruction, qualitative predictions and management: the case of a freshwater ecosystemOikos83, 93- 106.

Neutel, A.M., Heesterbeek, J.A.P. & de Ruiter, P.C. (2002) Stability in real food webs: Weak links in long loops.Science,296, 1120-1123.

& Thorne, M.A.S. (2014). Interaction strengths in balanced carbon cycles and the absence of a relation between ecosystem complexity and stability.

While feedback means that one problem can cause many more, it also means that one solution can tr…The current threat of climate change and habitat destruction demands that we scientists, students, and policy makers – learn to think about ecosystems and ecological processes in terms of feedbacks. Discuss!

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The Feedback Loop

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For many years the motor controller was a box which provided the motor speed control and enabled the motor to adapt to variations in the load. Designs were often lossy or they provided only crude increments in the parameters controlled.

Modern controllers may incorporate both power electronics and microprocessors enabling the control box to take on many more tasks and to carry them out with greater precision. These tasks include:

(speed, torque and efficiency of the machine or the position of its moving elements.)

Enabling self starting of the motor.

Protecting the motor and the controller itself from damage or abuse.

In an open loop control system the controlling parameters are fixed or set by an operator and the system finds its own equilibrium state.

In the case of a motor the desired operating equilibrium may be the motor speed or its angular position. The controlling parameters such as the supply voltage or the load on the motor may or may not be under the control of the operator.

If any of the parameters such as the load or the supply voltage are changed then the motor will find a new equilibrium state, in this case it will settle at a different speed. The actual equilibrium state can be changed by forcing a change in the parameters over which the operator has control.

Once the initial operating parameters have been set, an open loop system is not responsive to subsequent changes or disturbances in the system operating environment such as temperature and pressure, or to varying demands on the system such as power delivery or load conditions.

For continual monitoring and control over the operating state of a system without operator intervention, for more precision or faster response, automatic control systems are needed.

To meet these requirements closed loop systems are necessary. Also called feedback control systems, or negative feedback systems, they allow the user to set a desired operating state as a target or reference and the control system will automatically move the system to the desired operating point and maintain it at that point thereafter.

A sensor is used to monitor the actual operating state of the system and to feed back to the input of the controller an analogue or digital signal representing the output state. The actual and desired or reference states are continually compared and if the actual state is different from the reference state an error signal is generated which the controller uses to force a change in the controllable parameters to eliminate the error by driving the system back towards the desired operating point.

Loop GainThe error signal is usually very small so the controlling circuit or mechanism must contain a high gain error amplifier to provide the controlling signal with the power to affect the change.

The amplification provided in the loop is called the loop gain.

Loop DelayThe response is not always instantaneous as there is usually a delay between sensing the error, or aiming at a new position, and eliminating the error or moving to the new desired position. This delay is called the loop delay.

In mechanical systems the delay may be due to the inertia associated with the lower acceleration possible in getting a large mass to move when a force is applied.

In electrical circuits the delay may be associated with the inductive elements in the circuit which reduce the possible rate of current build up in the circuit when a voltage is applied.

Closed loop control systems must act very quickly to implement the error correction without delay, before the system has time to change to a different state. Otherwise the system will possibly become unstable.

When there is a time lag between sensing of the error and the completion of the corrective action and the loop gain is large enough the system the system may overshoot. If this happens the error will then be in the opposite direction and the control system will also reverse its direction of action in order to correct this new error. The result will be that the actual position will oscillate about the desired position. This instability is called hunting as the system hunts to find its aiming point.

In the worst case, the delayed error correcting response will arrive 180 degrees out of phase with the disturbance it is trying to eleiminate. When this happens the direction of the system response will not act so as to eliminate the error, instead it will reinforce the error. Thus the delay has changed the system response from negative feedback to positive feedback and the system will be critically unstable.

The diagrams below show the response of a control system to a small disturbance.

TheNyquistStability Criterionis used to predict whether or not a system is unstable from a knowledge of the loop gain and the loop delay as follows

If the loop gain is unity ot greater at the frequency of an input sinusoid where the time delay in the system is equal to half of a cycle period, the sytem will be unstable.

In practical terms, a system with high electrical or mechanical inertia will have a slow response (long delay). With a low magnitude, error correcting action (mechanical force or electrical voltage) the system will be slow in responding (speeding up) but because it is slow, it will also have a low momentum and will tend to settle at the desired operating point when the error correcting force is removed.

The delay in implementing the corrective action however depends on the loop gain.

If, in the same system, the error correcting force is high (amplified / higher loop gain), as in a fast acting system, the system will respond (get moving) more quickly (shorter delay) but it will have correspondingly higher momentum (higher speed of response). When the error correcting force is removed, like any high inertia system, the systems momentum will keep it moving and it will overshoot the target position. Applying the error signal in the opposite direction to bring the system back to its target will cause it to overshoot in the opposite direction.

Nyquist shows how much delay can be tolerated in a system with unity loop gain and defines the point at which the system becomes unstable

In the example of a DC electric motor, the desired operating state may be a particular speed. A tachometer is used to measure the actual speed and this is compared to the reference speed. If it is different, an error signal, whose magnitude and polarity correspond to the difference between the reference and the actual speeds, is fed to a voltage controller to change the motor speed so as to reduce the error signal. When the motor is operating at the desired speed the error signal will be zero and the motor will maintain that speed.

, named after three basic ways of manipulating the error information.

– Proportional error correction multiplies the error by a (negative) constant

, and adds it to the controlled quantity.

– Integral error correction incorporates past experience. It integrates the error over a period of time, and then multiplies it by a (negative) constant

and adds it to the controlled quantity. Equilibrium is based on the average error and avoids oscillation and overshoot providing a more stable system.

– Derivative error correction is based on the rate of change of the error and takes into account future expectations. It is used in so called Predictive Controllers. The first derivative of the error over time is calculated, and multiplied by another (negative) constant

, and also added to the controlled quantity. The derivative term provides a rapid response to a change in the system.

Combinations of all three methods of error processing are often used simultaneously in PID controllers to address different system performance priorities. Where noise may be a problem, the derivative term is not used.

PID controllers are also called 3 term controllers.

Motor controllers may be simple open loop systems or they may incorporate several nested closed loop systems operating simultaneously. For example closed loop controls may be used to synchronise the excitation of the stator poles with the angular position of the rotor or simply to control motor speed or the angular position of the rotor.

When an electrical machine is required to work as both a motor and a generator in both forward and reverse directions this is said to be four quadrant operation. A simple motor which only runs in one direction and is never driven as a generator is an example of a single quadrant application. A motor designed for automotive use which must run in forward and reverse directions and which must provide regenerative braking in both directions needs a four quadrant controller.

Control systems for four quadrant applications will obviously be more complex than single quadrant controls.

Controllers may have some or all of the following functions many of which have been implemented in integrated circuits.

One of the major attractions of brushed DC motors is the simplicity of the controls. The speed is proportional to the voltage and the torque is proportional to the current.

Speed control in brushed DC motors used to be accomplished by varying the supply voltage using lossy rheostats to drop the voltage. The speed of shunt wound DC motors can also be controlled byfield weakening. Nowadays electronic voltage control is employed. See below.

Simple open loop voltage control is sufficient when the motor has a fixed load, however open loop voltage control can not respond to changes in the load on the motor. If the load changes, the motor speed will also change. If the load is increased, the motor must deliver more torque to reach an equilibrium position and this needs more current. The motor consequently slows down, reducing the back EMF so that more current flows. To maintain the desired speed, a change in the voltage is needed to provide the necessary current required by the new load conditions. Automatic control of the speed can only be accomplished in a closed loop system. This uses a tachogenerator on the output shaft to feedback a measure of the actual speed. When this is compared with the desired speed, a speed error signal is generated which is used to change the input voltage to the motor to drive it towards the desired speed. Note – This is essentially avoltage controlsystem since the tachogenerator usually provides a DC voltage output which is compared with a reference input voltage.

Voltage control alone may be insufficient to cater for wide, fast changing load conditions on the motor since the voltage controller may call for currents in excess of the motors design limits. A separate current feedback loop may be required to provide automaticcurrent control. The current control loop must be nested within the voltage control loop. This allows the voltage control loop to deliver more current but it can not override the current control which ensures that the current remains within the limits set by the current control loop.

Brushless DC motors are powered by a pulsed DC supply to create a rotating field and the speed is synchronous with the frequency of the rotating field. Speed is controlled by varying the supply frequency. See alsoInvertersbelow.

The speed of AC motors generally depends on the frequency of the supply voltage and the number of magnetic poles per phase in the stator. Early speed controllers depended on switching in different numbers of poles and control was only available manually and in crude steps. Modern electronicinvertersmake continuously variable frequency supplies possible permitting closed loop speed control. For speed control in induction motors however the supply voltage must change in unison with the frequency. This requires a specialVolts/Hertz controller.

If the application requires direct control over the motor torque rather than the speed, in simple machines this can be accomplished by controlling the current, which is proportional to the torque, and omitting the speed control loop. For more precise control,vector controllersare used.

It is no longer necessary to use energy wasting rheostats to provide a variable voltage.

Modern controllers useswitching regulatorsor chopper circuits to provide a variable DC voltage from a fixed DC supply. The DC supply is switched on and off at high frequency (typically 10 kHz or more) using electronic switching devices such asMOSFETs,IGBTs orGTOs to provide a pulsed DC wave form. The average level of the output voltage can be controlled by varying the duty cycle of the chopper.

AC voltages can be similarly controlled using bi-directional pulses to represent the sinusoidal wave.

Various PWM schemes are possible. Only one is shown here. By varying the pulse width, the amplitude of the sine wave can be changed.

Variable voltages can also be generated by using fixed pulse widths but by varying instead the pulse amplitude (Pulse Amplitude Modulation – PAM) or the pulse repetition frequency (Pulse Frequency Modulation – PFM).

The DC output from choppers and PWM circuits is notoriously plagued by high harmonic content. Most DC motors however can tolerate a pulsed DC supply since the inductance of the motor itself and the mechanical inertia of the rotor help to smooth out the variations in the supply voltage. Since there is no current flowing when the switching device is off, the technique is relatively loss ggingmay occur if the chopper frequency is too low.

A voltage controller may be activated manually in an open loop system but for continuous voltage control, an inverter must be incorporated into a feedback loop in a closed loop system. The control system monitors the actual output voltage and provides a control signal, which may be an analogue or digital representation of the error signal, to the pulse width modulator to correct any deviations. When voltage control is used for speed control the error signal may be derived from a tachogenerator on the motor output shaft.

Electronic voltage control is also an essential part of many generator applications. In automotive systems the generator or alternator is driven at a variable speed which depends directly on the engine speed. It must give its full voltage output at the lowest speed but the voltage must be maintained as the engine speed rises. Alternators used in 12 Volt systems usually have built involtage regulation. In HEV applications a chopper regulator is used at the output of the generator to maintain the voltage at the DC link within strict limits to avoid damaging the battery. When the battery is fully charged, the batterys own management system disconnects it from the supply to prevent overcharging.

For low power applications a series orlinear regulatoris often used. It is less efficient than a switching regulator since the variations in voltage must be taken up, and the associated power dissipated, by the volt dropping series transistor but it provides a pure DC. Series regulators are not suitable for high power applications such as electric traction where efficiency is paramount.

With AC supplies,Thyristors (SCR)scan be used in series with the load to create a variable voltage by blocking the passage of current to the load for the initial part of the cycle and turning the current on by applying a signal to the gate of the SCR. A single SCR only affects one polarity of the waveform. To switch both the positive and negative going current requires two SCRs connected in parallel and in opposite polarity or a triac (bidirectional SCR). By varying the delay (the phase angle) before the current is turned on, the average current, and thus the average voltage seen by the load, can be varied as shown below.

This is the same principle as used in light dimmer switches.

Gate turn off thyristors (GTOs)can be used to switch off the current as well as switching it on allowing more control over the duration of the current through the device.

In many motor applications the motor current may lag the supply voltage due to the inductance in the circuit and it is often desirable to control the current directly, rather than the voltage, to obtain more precise or faster control of the current and hence the torque. In this case a shunt resistor or a current transformer is used to monitor the current. The difference between the actual and reference currents is used in a high gain feedback loop to provide the necessary current regulation.

Current control is particularly important for induction motors to protect the motor from excessive start up currents. A current feedback signal is used to change the firing angle of thyristors in the rectifier or inverter circuits to limit the current within its reference value.

This a generic term for circuits which may provide AC or DC outputs from either AC (mains frequency) or DC (battery) supply lines. They include power bridges for rectifying the AC supply and inverters for generating an AC waveform from a battery supply.

Buck and boost converters are DC-DC converters, the DC equivalent of AC transformers.

The buck converter is used to reduce the DC voltage. Thechopperabove is an example of a step down DC converter.

The boost converter is used to step up the DC voltage.

The circuit below can step up or step down the input voltage by varying the duty cycle of the transistor switch.

The transistor switch turns the supply voltage to the LC circuit on and off. When the transistor is on, the inductor is charged up and the diode cuts off the capacitor. When the transistor turns off, the inductor discharges, via the diode, through the capacitor charging it up. Note that the polarity of the output voltage is the reverse of the input voltage. With a low duty cycle when the transistor is off more than 50% of the time, the voltage which appears at the output is lower than the supply voltage and the circuit acts as a step down transformer. With a high duty cycle when the transistor is switched on more than it is off, the voltage builds up on the capacitor and the output voltage exceeds the supply voltage. Voltage regulation is thus provided by varying the duty cycle.

Inverters provide a controlled alternating current (AC) supply from a DC or AC source. There are two main classes of applications:

Inverters designed to deliver regulated AC mains power from sources which may have a variable input voltage (either AC or DC) or in the case of AC input power, a variable frequency input. Such applications may include emergency generating sets, uninterruptible power supplies (UPS) or distributed power generation from wind and other intermittent resources. All must deliver a fixed output voltage and frequency to the load since the applications expect it and may depend on it.

On the other hand, many applications require inverters to accept a fixed AC voltage and frequency from the mains and to provide a different or variable voltage and frequency for applications such as motor speed control. .

In both of these designs, a bridge rectifier is used to provide the intermediate DC power through a DC Link to a regular AC inverter.

The circuit below shows the principle of such an inverter designed for three phase applications.

Three phase variable frequency inverter

The three phase sinusoidal input is fed to a simple diode full wave bridge rectifier block delivering a fixed voltage to the inverter. The connection between the rectifier and the inverter is known as the DC Link. The inverter transistors are switched on in the sequence of their numbers as shown in the diagram with a time difference if T/6 and each transistor is kept on for a duration of T/4 where T is the time period for each complete cycle. The example above provides six possible current configurations and is known as a six step inverter.

The diodes connected across the switching transistors are known as freewheel or flywheel diodes. Their purpose is to provide a current bypass path around the transistor to protect it from the dissipation of the stored energy in the inductive load (the motor) when the transistor is switched off. The current through the diode freewheels until all the energy in the inductive load is dissipated.

The output line voltage wave form for each phase is shown below.

This inverter frequency reference may simply be a voltage applied to the input of a Voltage Controlled Oscillator (VCO) examples of which are commonly available as integrated circuit chips, or it may be derived from a microprocessor clock. Digital logic circuits are used to derive the timed trigger pulses to the inverter switches from the frequency reference source. In the case of generators delivering mains power, the frequency reference value will be fixed.

The amplitude of the output wave is determined by the level of the DC supply voltage to the inverter block but it can be varied by thyristor (SCR) control of the rectifier circuit to provide a variable voltage at the DC link.

Instead of transistor switches, the inverter may use MOSFETs, IGBTs or SCRs.

Free-wheeling diodes connected across the transistors protect them from reverse bias inductive surges due to motor field decay which results when the transistors turn off by providing free wheeling paths for the stored energy.

The waveforms for traction applications are often stepped waves rather than pure sinusoids since they are easier to generate and the motor itself smoothes out the wave.

Variable frequency inverters are used when variable speed control is required. The frequency of the wave is controlled by a variable frequency clock which initiates the pulses.

For speed control in AC machines the voltage and frequency must vary in unison. SeeAC motor speed control. In open loop systems the operating point is set by a speed reference and the equilibrium speed is determined by the load torque. A closed loop system allows a fixed speed to be set. This requires a tachogenerator to provide a feedback of the actual speed for comparison with the desired speed. If there is a difference, an error signal is generated to bring the actual speed into line with the reference speed by adjusting both the voltage and the frequency so as to eliminate the speed difference.

See alsobrushless DC motor speed controland examples ofgenerator speed controls.

Volts/Hertz controlis needed for speed control of induction motors. In an open loop system the control system converts the desired speed to a frequency reference input to a variable frequency, variable voltage inverter. At the same time it multiplies the frequency reference by the Volts/Hertz characteristic ratio of the motor to provide the corresponding voltage reference to the inverter. Changing the speed reference will then cause the voltage and frequency outputs from the inverter to change in unison.

In a closed loop system a speed feedback signal provided from a tachogenerator on the motor output shaft is used in the control loop to derive a speed error signal to drive a Volts/Hertz control function similar to the one outlined above.

As with large DC motors, speed control is normally accompanied by current control.

The cycloconverter converts AC supply frequency directly to a variable frequency AC without the intermediate DC link stage.

The system is complex and works by sampling the voltage of each phase of the AC supply and synthesising the desired output waveform by switching on to the load for the duration of the sampling period, the phase whose voltage is closest to the desired voltage at the instant of sampling. The output waveform is severely distorted and the capability of induction motors to cope with the very high harmonic content limits the maximum frequency for which the system can be used.

Cycloconverters are only suitable for very low frequencies, up to 30% of the input frequency. They are used for low speed high power drives to eliminate the need for a gearbox in heavy rolling and crushing mills and in traction applications for trains and ships.

All motors need a magnetising current and a torque producing current. In a brushed DC motor, these two currents are fed to two different windings. The magnetising current is fed to the stator or field winding and the torque producing current is fed to the rotor winding. This allows independent control of both the stator and the rotor fields. However in brushless motors such as permanent magnet motors or induction motors it is not possible to control the rotor field directly since there are no connections to it. Because the parameters to be controlled can not be measured, their values must be derived from parameters which can be measured and controlled. The only input over which control is possible is the input current supplied to the stator.

The actual stator current is the vector sum of two current vectors, the inductive (phase delayed) magnetising current vector producing the flux in the air gap and thein phase, torque producing, current. To change the torque we need to change thein phase, torque producing, current but because we want the air gap flux to remain constant at its optimum level, the magnetising current should also remain unchanged when the torque changes.

Vector Control or Field Oriented Control is a method of independently varying the magnitude and phase of the stator current vectors to adapt to the instantaneous speed and torque demands on the motor.

It enables parameters over which no direct control is possible to be changed by changing instead, parameters which can be measured and controlled.

For many applications vector control is not necessary, but for precision control, optimum efficiency and fast response, control over the rotor field is needed and alternative methods of indirect control have been developed. Because of the low cost of computing power, vector control is being used in more and more brushless motor applications.

Maximum current-to-torque power conversion, fast transient response, precise control of torque, speed and position.

Rotating flux to be maintained at 90 degrees to the rotor flux.

Available information (status of stator voltages and currents and rotor position and/or speed).

Two independent control loops to provide control of the magnetising and torque producing current vectors.

Mathematical transforms to analyse input signals from the stator and calculate any deviation from the desired conditions of the rotor.

Mathematical inverse transforms to convert the rotor error signal back into control signals to be applied to the stator to counteract the error.

A pulse width modulated (PWM) inverter providing power to the motor.

Stator input voltage waveforms of the correct amplitude, frequency and phase to effect the change.

Uses position sensors and complex mathematical transforms

Sensorless Uses even more complex mathematical transforms

(Both of the above methods use current sensors for current control of the stator windings)

Samples status and provides control signals at 20 kHz to provide continuous control.

Low speed control, efficiency improvement, smaller motors.

The good news is that a detailed knowledge of the process involved is not necessary since most of these tasks are implemented in integrated circuits and incorporated into the motor design. But read on to find out how the overall system is used.

Despite its many advantages, the venerable induction motor is relatively slow to respond to changes in load conditions or user commands for changes in speed. This is mainly because the rotor current can not instantaneously follow the applied voltage due to the delay caused by the inductance of the motors windings.

During the transition period the flux amplitude and its angle with respect to the rotor must be maintained so that the desired torque can be developed.

Torque also depends on the magnitude of the flux but this depends on the inductive component of the current and can not be changed instantaneously. In any case the flux density is set to its optimum point before saturation occurs.

Vector control is a way of changing the in phase current vector without changing the inductive magnetising current vector so that the machine response time is not subject to inductive delay.

The inductive phase lag noted above also causes an instantaneous loss of torque and reduced efficiency because the torque producing flux from the stator is not acting at 90 electrical degrees to the rotor field.

The torque on the rotor of any motor is at its maximum when the magnetic field due to the rotor is at right angles to the field due to the stator. SeeInteractive Fields

The vector control system provides instantaneous adjustments to the stator currents to control the position of the rotor with respect to the moving flux wave thus avoiding losses due to

Homeostasis positive negative feedback mechanisms

You are here:HomeThe BasicsHomeostasis: positive/ negative feedback mechanisms

The biological definition of homeostasis is the tendency of an organism or cell to regulate its internal environment and maintain equilibrium, usually by a system of feedback controls, so as to stabilize health and functioning. Generally, the body is in homeostasis when its needs are met and its functioning properly.

Every organ in the body contributes to homeostasis. A complex set of chemical, thermal, and neural factors interact in complex ways, both helping and hindering the body while it works to maintain homeostasis.

To maintain homeostasis, communication within the body is essential. The image below is an example of how a homeostatic control system works. Here is a brief explanation:

produces a change to a variable (the factor being regulated).

detects the change. The receptor monitors the environment and responds to change (stimuli).

information travels along the (afferent) pathway to the control center. The control center determines the appropriate response and course of action.

information sent from the control center travels down the (efferent) pathway to the effector.

a response from the effector balances out the original stimulus to maintain homeostasis.

Interactions among the elements of a homeostatic control system maintain stable internal conditions by using positive and negative feedback mechanisms.

Think of it as an extremely complex balancing act. Heres a few more definitions you may want to know.

Afferent pathways carry nerve impulses into the central nervous system. For instance, if you felt scorching heat on your hand, the message would travel through afferent pathways to your central nervous system.

Efferent pathways carry nerve impulses away from the central nervous system to effectors (muscles, glands).

The feeling of heat would travel through an afferent pathway to the central nervous system. It would then interact with the effector and travel down the efferent pathway, eventually making the person remove their hand from the scorching heat.

Almost all homeostatic control mechanisms are negative feedback mechanisms. These mechanisms change the variable back to its original state or ideal value.

A good example of a negative feedback mechanism is a home thermostat (heating system). The thermostat contains the receptor (thermometer) and control center. If the heating system is set at 70 degrees Fahrenheit, the heat (effector) is turned on if the temperature drops below 70 degrees Fahrenheit. After the heater heats the house to 70 degrees Fahrenheit, it shuts off effectively maintaining the ideal temperature.

The control of blood sugar (glucose) by insulin is another good example of a negative feedback mechanism. When blood sugar rises, receptors in the body sense a change . In turn, the control center (pancreas) secretes insulin into the blood effectively lowering blood sugar levels. Once blood sugar levels reach homeostasis, the pancreas stops releasing insulin.

These are just two examples of negative feedback mechanisms within our body, there are 100s, can you think of a few more?

A positive feedback mechanism is the exact opposite of a negative feedback mechanism. With negative feedback, the output reduces the original effect of the stimulus. In a positive feedback system, the output enhances the original stimulus. A good example of a positive feedback system is child birth. During labor, a hormone called oxytocin is released that intensifies and speeds up contractions. The increase in contractions causes more oxytocin to be released and the cycle goes on until the baby is born. The birth ends the release of oxytocin and ends the positive feedback mechanism.

Another good example of a positive feedback mechanism is blood clotting. Once a vessel is damaged, platelets start to cling to the injured site and release chemicals that attract more platelets. The platelets continue to pile up and release chemicals until a clot is formed.

Just remember that positive feedback mechanisms enhance the original stimulus and negative feedback mechanisms inhibit it.

thank you so much for this!!! this is exactly what I needed for my biology report!! 😀

lol my names destiny but ya it helped me too haha

thanks for the info.. starting my A&P class next week and decided to do some early reading and studying.. your explanation and examples really helped me.. thanks again

thank you ever so much!! best illustration thus far.

yes your information was exactly what i was looking for, thanks very much.

Great site and plan to use it much more. Will say though, still feel i am missing a piece when it comes to positive and negative feedback. example you gave for positive about the cut arm. Why would it not be negative feedback if the platelet are released in response to a changed environmentdoes that make sense?

Hey Jennie. I see your point of view and understand why it can be confusing. The reason wound healing is considered a positive feedback mechanism is because the output enhances the original stimulus. If a cut occurs, the body sends platelets and cells to the site. The platelets and cells fight invading pathogens and produce a clot. When the clot forms and the wound heals, the inflammation response and output end.

Negative feedback changes a variable back to its original value and is constantly adjusting within the body. If your temperature is to high, a negative feedback loop works to lower it. If your temperature is low, it will bring it back up. Its a balancing act.

Positive feedback only occurs in certain situations and has an ending, it does not constantly adjust. If you get a cut, a positive feedback loop works to heal it, then it stops. If you go into labor, the loop continues until you deliver, then its over and you go back to your original state. Think if you werent pregnant but felt like you were in labor all the time. Luckily, we have positive feedback loops! I hope this enhances your understanding of homeostasis and positive/negative feedback. Thanks for visiting the site Jennie!

I was struggling so much to understand this topic and now I understand completely!!! This is so damn amazing

yahh realy so easy to understand this topic

Thanksto all of u by creating this kind of page I.e full of information. ..blessing.

Had no idea what positive feedback meant . Now its in here.

This is one of the topics I failed to understand in class more especially in high school. But now here Im doing it again. Thanx for the information as it is helpful, not only to me but a lot of people will just find it beneficial.

Nice one Can I get more examples of positive feed back.. Tanx

Thanks so much,at least now Ive understood the issue of negative and positive feedback mechanisms

Thank u so much, ur simple bacic explanations has helped me to understand my entire work

Thank you! This is exactly help me to complete my test hehehehehe

Thanks for this illustration,it helps me more to understanding this topic.

Thanks u really helped me to understand

made it simple but more examples should be given.

This is exactly the info I was looking for, thumbs up!!

Thank yhu very studying mbbs.really need this and I find thisen its was really helpful towards my physiology.test..thanks once again

hi can i can any one help me with who the author is i would like to use some bits and am needing a reference thanks

Regarding to the childbrith, or the positive feedback mechanism in general, how can we determine the set point? And is it always the hypothalamus the control center?

This is awesome. Honestly I have been struggling to understand this in my biochemistry classes but after reading and digesting this, I doubt if I can be thrown into oblivion. Thanks pal. More examples would be appreciated if you have others.

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Human Body Organ Systems: An Orientation

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Homeostasis: positive/ negative feedback mechanisms

If you study biology or medicine, having a solid understanding of homeostasis is extremely important. All living systems are based

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The heart is an extremely interesting and powerful pump. It operates by using an intrinsic control and conduction system that

Can you name the 11 organ systems of the human body from memory? If not, this may be a good

Did you know the digestive system is split into two main groups? Did you know one of the groups is

Nieman Journalism Lab

Tell me more: The Globe and Mail is slipping a little extra context into its stories (while explaining its editorial thinking along the way)

How much influence does the media really have over elections? Digging into the data

My sense is that what we have here is a feedback loop. Does media attention increase a candidates standing in the polls? Yes. Does a candidates standing in the polls increase media attention? Also yes.

Whether your favorite candidate is popular or unpopular, its always popular to blame the media. We see a lot of this right now in discussions of whyTrumpis in the lead or whySandersisnt.

Usually the complaints have to do with what the media is saying about a candidate. But another theory says that its theattentionthat matters. Good news or bad maybe the important thing is just to be talked about.

New Pew data: More Americans are getting news on Facebook and TwitterOr maybe professional journalists have very little influence at all.Many peoplenow get their news by clicking on articles from social media, where your friends and afiltering algorithmdecide what you see.

So does the media still matter? Does attention get results for candidates, regardless of what is said? And if it does, how should journalists cover elections fairly and responsibly? These are the questions I wanted to try to answer, at least as they relate the current U.S. presidentialprimaries.

These are big questions about how the American political system works, far too big for simple answers. But you have to start somewhere, so I decided to compare the number of times each 2016 candidate has been mentioned in the U.S. mainstream media with their standing in national primary polls. To my surprise, the two line up almost exactly.

Percentage of online media mentions and percentage primary voters supporting each candidate, Q4 2015.Source.

This chart shows the number of times a candidates full name appeared in thetop 25 online news sources, as a percentage of all mentions, for October to December of 2015. (Republican candidates were mentioned about twice as often as Democratic candidates overall, but this chart compares each candidate to the others within their party.) Theres an uncanny agreement between the media attention and each candidates standing in national primary polls. Its a textbook correlation.

Depending on what corner of the political universe you come from, it may surprise you to learn that both Trump and Sanders were covered in proportion to their poll results at least online. Pretty much everyone was. The exceptions are Jeb Bush, who seems to have been covered twice as much as his standing would suggest, and Carson, who might have been slightly under-covered.

By simply counting the number of mentions, were completely ignoring what journalists are actually saying, including whether the coverage was positive or negative. This data doesnt say anything at all about tone or frame or even what issues were discussed. All of these things might be very important in the larger context of democracy, but they seem to be less important in terms of primary poll results. While the story surely matters, it doesnt seem to matter as much as the attention. In particular, Trump has received much more negative coverage than his GOP competitors, tolittle apparent effect.

I admit I was a bit shocked to discover how closely the percentage of media mentions and the percentage of voter support align. But Im also not the first to notice. Nate Silver found thatthis pattern holds in U.S. primary elections going back to 1980, though his model also incorporated favorability ratings. This correlation has alsoby previous political science researchers, though I havent been able to find anywhere its been seriously investigated.

So whats going on here? How do all the numbers on this chart just line up? Does this mean the media exert near-total control over the political process? Fortunately, no. To begin with, national primary pollsdont predict the eventual nomineevery well; state polls matter much more, because the nominating process happens one state at a time. But it seems reasonable to imagine that media attention hassomeeffect on the polls. Yet journalists alsorespondto the polls, which means it isnt clear whats causing what.

If youre worried about the medias influence youre thinking of a causal relationship like this:

But there are twoother waysthat these variables can become highly correlated. First, causality could go the other way. The polls could drive the media.

This isnt completely insane. Journalists have to follow audience attention or risk getting ignored. And if voters are also readers, a candidate who is twice as popular might get twice the number of views and shares. That matters when youre deciding what to cover though its hardly the only consideration. More on that later.

Theres one more way to get a close relationship between media and polls: something else could be driving both of them. For example, attention on social media could drive both. A single post can go viral and reach millions without any involvement from professional journalists. Or perhaps endorsements from famous people and organizations are the key to influence, as political scientists have longsuspected. And then there are the candidates themselves: anything they do might make them more (or less!) favorable with both the media and the public. In short we need to considerevery other thing, and many of these things will drive media attention and voter preference in the same direction, causing a correlation like the one weve seen.

These are the basic causal forces, the only possible ways that media attention and polling results can become so closely aligned. Were going to need more information to figure out what is causing what.

One way to test for causality is to ask whether a change in coverage precedes a change in the polls, or vice versa. Heres the number of articles mentioning the right-wing U.K. Independence Party (UKIP) versus poll results, tracked over 11 years in the British press.

Number of articles mentioning UKIP (orange) versus percentage who say they would vote for UKIP (blue). FromDoes Public Support for UKIP Drive Media Coverage or Does Media Coverage Drive Support for UKIPby James Murphy.

In this chart by James Murphy of Southhampton University, were looking at changes across time, rather than between parties. Yet once again, coverage and popularity follow each other closely. To determine which came first, Murphy built astatistical modelthat tries to predict this months polls from the previous months coverage, and vice versa. Whichever direction works better, thats the way the cause runs. But the results were inconclusive they depended on exactly how the model was put together. This suggests that the causality goes both ways.

Heres a similar chart of popularity and coverage over time for Trump:

Weekly online media mentions of Trump vs. national primary polls.Source.

Trumps polls and mentions rose at about the same rate after he announced his candidacy, so at first glance it looks like the two are tied together. But media spikes dont always translate into polling spikes: Both debates produced a spike in coverage, but the polls actually decreased in the short term. The burst of coverage after he announced his plan to exclude Muslims does seem to line up with a bump in popularity, though.

John Sides of George Washington University has done a statisticalanalysisto try to tease out the causality in Trumps data and, once again, the results dont clearly favor the chicken or the egg. Instead, it seems that the media and the polls drive each other loosely. Most of the other candidates show the same general pattern.

Weekly online media coverage of candidates vs. national primary polls.Source.

We typically see a rise after the candidate announcement, then general agreement with the level of media coverage even though the peaks dont line up. Clinton seems to be the exception: Her popularity seems to have less to do with coverage volume than any other candidate. Maybe thats because weve known for a very long time that she was going to run, and we should really plot this chart back another year or two.

My sense is that what we have here is a feedback loop. Does media attention increase a candidates standing in the polls? Yes. Does a candidates standing in the polls increase media attention? Also yes. And everything else which sways both journalists and voters in the same direction just increases the correlation. The media and the public and the candidates are embedded in a system where every part affects every other.

Its all of these forces acting in concert that tend to bind media attention and popularity together. Its not that media attention has no effect we have good reason to believe it does, both from this data and fromother research. Its just that the media is not all powerful, despite what the close correlation suggests.

Faced with the awesome ability to influence the outcome of an election just by drawing attention to a candidate, howshouldthe media cover an election?

No editor is sitting there saying:Hey, Cruz gained five points, lets cover him 5 percent more.But journalists do respond to audience attention. Reporters and editors are driven by lots of different demand signals, such as how many people read yesterdays article about a candidate, or how many people are talking about a candidate on social media or lets be honest here how popular someone seems to be based on how much coverage they are getting from other journalists! Some newsrooms even plan coverage based on how many people are searching for a given topic.

The media is regularly criticized for chasing popularity, and in this sense its true. Bernie Sanderssaysthe corporate media trivialize the issues and only care about profits. There is certainly no profit without readers theres no funding either, if youre a nonprofit newsroom. The rapper Commonsaysthe integrity of the media is gone when journalists decide were going to show Donald Trump because we know its about numbers. And these complaints are not wrong. I began writing this piece to explore the medias relationship to Trump in part because I knew a piece about Trump was likely to be widely read!

Yet for all the newsroom profit pressure and manic metric checking, journalists dontonlychase popularity. The American media cover a great many things that few people pay attention to, especially international stories. For example, there was extensivecoverage of bombings in Lebanona day before the Paris attacks, despite complaints to the contrary. Theres an ongoing, thoughtful conversation among journalists abouthow to balance what gets clicks with whats important. That is, whatjournaliststhink is important. Ill say this for writing what the audience wants to read: Its democratic.

So should a candidate get media attention according to how many people want to read about them? On some level, yes. But if you think Trump shouldnt be leading or Sanders should be, this probably doesnt seem fair to you. To the degree that media attention causes a candidate to become more popular, theres a winner-take-all effect here: The leading candidate will get the most coverage, boosting their lead. Meanwhile, the media has the potential to trap a candidate in last place because they cant get the coverage they would need in order to rise in the polls.

But whats the alternative? Should journalists cover every candidate equally? This might make a certain amount of sense in the general election, where we only have two major parties. The FCC still enforces theequal time rulewhich says that if a radio or TV network gives one candidate airtime, they have to give the same amount to other candidates. But that rule doesnt apply to news programs, and thats probably for the best. Its ridiculous to imagine journalists struggling to reach story quotas, so that each candidate gets the same amount of press.

But if not equal time, should journalists strive for some other redistribution of attention? This would necessarily mean less coverage for the leaders and more for everyone else. This might lead to more competitive elections, in that it would counter the winner-take-all tendency of the current system. But it would also mean intentionallynotcovering Trump as much. This might balance things out in an abstract sort of way, but it would also open the media to charges of censorship and those charges would not be without merit.

Objectivity and the decades-long shift from just the facts to what does it mean?It also wont work to suggest the press should just report current events or whatever is newsworthy, as if the news makes itself. Journalism has becomeless and less about eventsover the last 50 years, and more and more about context and analysis. And thats okay: Politicians and brands are their own media channels now. If all you want to know is what a candidate did today, you can just follow them on social media no need for professional journalists at all. Journalists have to add value in other ways now, such as providing context or digging deeper. Theres no obviously right number of stories about a candidate.

Somewhere, somehow, professional journalists have to decide who gets covered and any formula they could choose is going to appear biased to someone. In the end, the candidates who attack the media are right about one thing: The press is a political player in its own right. Theres just no way to avoid that when attention is valuable.

Jonathan Strayis a journalist and computer scientist who leads theOverviewproject andteachescomputational journalism at Columbia.

Photo of media interviewing Jeb Bush in Hudson, New Hampshire byMichael Vadonused under a Creative Commons license.

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Stray, Jonathan. How much influence does the media really have over elections? Digging into the data.Nieman Journalism Lab. Nieman Foundation for Journalism at Harvard, 11 Jan. 2016. Web. 7 Jul. 2018.

Stray, J. (2016, Jan. 11). How much influence does the media really have over elections? Digging into the data.Nieman Journalism Lab. Retrieved July 7, 2018, from

Stray, Jonathan. How much influence does the media really have over elections? Digging into the data.Nieman Journalism Lab. Last modified January 11, 2016. Accessed July 7, 2018.

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As a news organization, its perhaps an opportunity for us to be helping people fill those gaps without forcing them to go to Wikipedia or start Googling things, just to try to get the background they crave on a story.

Water in a news desert: New Jersey is spending $5 million to fund innovation in local news

The dollar amount isnt huge, and it will barely put a dent in the crisis of local news. But its also an official statement that communities information voids are a problem worthy of government attention.

Thanks to California, a news site (or other business) now has to let you cancel your subscription online

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Tell me more: The Globe and Mail is slipping a little extra context into its stories (while explaining its editorial thinking along the way)

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Water in a news desert: New Jersey is spending $5 million to fund innovation in local news

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The Inner Loop

The inner loop of the Net Promoter Systempromotes individual learning. It lets frontline employees and teams hear both positive and constructive customer feedback directly and immediately. The inner loop enables them to implement whatever changes they can make on their own.

Net Promoter®companies ask their customers for feedback regularly. They may do so after an individual transaction, after a series of interactions or simply once every so often, to assess the quality of their relationship with a customer. They ask not only how likely the customer would be to recommend the company or its products but also that all-important second question: Why? The feedback thus provides both quantitative ratings and qualitative comments.

As the first step in the inner loop, companies channel the feedback to every employee who affected a given customers experience. It may go to the call-center rep or warehouse worker who served that customer. It may also go to product designers, pricing analysts and anybody else whose decisions and actions are relevant. This part of the inner loop must be designed right: The feedback has to be both granular and timely, and it has to lead to effective follow-up.

Granularity. Much of the systems feedback focuses on individual events, such as particular transactions or specific parts of the customers experience. The granularity allows employees to learn from what they did, to try something different and to observe the outcome.

Timeliness. If a company is asking for feedback about an interaction or transaction, the request has to go out right away, while the experience is still fresh in the customers mind. The feedback that comes in must flow to the relevant employees immediately, so that they will remember that customer.

With immediate feedback, call-center workers can learn why some customers feel upset; they can then try out different approaches for calming them until they find one that feels reliable. A product designer can hear exactly what buyers are saying about his teams latest model and can begin experimenting with potential improvements.

Follow-up. The inner loop is a closed loop. Customers provide feedback. It goes straight to the employees who can learn from it, closing the loop between customer and employee. Then the employee or supervisor takes the next step: closing the loop between company and customer by calling the customer back.

The follow-up call always begins with some nonjudgmental probing about the customers experience with the company. It typically includes a thank-you and a commitment to fix the customers problem wherever possible. But it isnt a scripted call; its an informal human interaction, which is why it cant be delegated to a third party or some central corporate group. Customers must come away feeling better about the company than they did before, and the company must learn more about customers needs, desires and experiences. .

Supervisors or knowledgeable peers can serve as a sounding board for the employees interpretation of the feedback and ideas about what to do differently. They broaden the list of alternatives under consideration and describe practices that have worked for others in similar situations. Employees can then try out new behaviors or new ways of doing things and report the results back to their coaches and fellow team members.

One of a coachs tasks is to help employees respond appropriately, separating the vast majority of customers who offer constructive feedback from the small minority who should really be encouraged to take their business elsewhere. The objective of the Net Promoter Systems inner loop isnt to satisfy the customer at all costs; the objective is to create profitable promoters.

In this short video, Rob Markey discusses how the inner loop offers powerful motivation for employees.

To discuss how our team can help your business, please

The Secret to Individual Learning and Connections with Customers

The key is enabling employees to get real-time feedback directly from customers.

Read our latestInsightson the Loyalty Blog

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Continuous Feedback Loop

byJeff SlaterDec 21, 2015Marketing AdvicePersonal Stories

Did you Achieve Your Goals in 2015?You start each year with unbridled enthusiasm and a game plan. 2015 was the year you expected to take share from your competitors or enter a new market. You had many new products that your team introduced and a spanking new ad campaign to get the word out. Your staff went through extensive training and appeared properly motivated. You had all our ducks in a row.

But somehow you failed to achieve the 2015 goals.

Sometimes the simple truth is thatthe marketplace for your product or service is always changing.What seemed like the right need for the market when you created your new product pipeline, may have already started to shift in a new direction. Your products and approach may have made sense from within the office, but twelve months later, when you go out to sell, it falls flat. We dont need to create a Rube Goldberg contraption to use a napkin.What we need is frequent feedback from customers.

Brands need an endless feedback loop that helps that adjust and keep recalculating. Those six features that were so important last year when your product development began to require reprioritization. You need the benefit ofa minimal viable product modelto help you keep reaffirming market needs.

Brands need a continuous feedback loop because while you are creating your new offering, your competitors have introduced something that changes the equation with those customers. When you competitor now offers three new features for free that you had planned to charge for, the equation changes. When the competition opens up a huge manufacturing site and needs to fill it, pricing pressures emerge. It should be no surprise that most markets are moving faster and competition is coming from inside and outside of your category. Ask a taxi driver if she saw Uber coming or ask Hilton if they predicted AirBnB as a competitor.

Today companies like P&G, GE and others are using methods to strip bare product offerings so that they can be more fluid in entering markets with new products. They cut development time dramatically by keeping to simpler less complicated offerings.

If you are introducing new products in 2016, here are a few suggestions to help with the launch.

Eliminate most of the new product offerings.

Constantly simplify and focus your teams.

Focus on just one or two product launches that have the strongest opportunities to solve critical customer

so you can get it into customers hands faster. Customer in B2B and B2C crave simple solutions, not complicated ones.

Resist flexing your own technical muscles.

You arent there to prove what cool stuff you can make. You are there to solve customers problems.

Only add more features and complexity if customers show significant evidence of demand

and a willingness to pay more. Score each feature to make sure you arent adding more than customers need to your offering.

Create a better feedback loop mechanism with your new product team and customers

so that everyone is solving the same obvious problem with the simplest solution

stop swinging for the fences for home runs

The best evidence of how important it is to have a continuous loop is your experiences with product and services. Next time you pick up a rental car. buy a pair of sneakers or order take-out from a restaurant ask yourself this question: have they made things easier or more complicated for you? Do they offer new products or services that help you solve your problem or do they make things more difficult for you? If you had been asked, what would you have advised they do differently that could have made the process smoother. Starbucks introduces an app so you can avoid the line. Simple. Focused. Problem-solving product.

Have they made things easier or more complicated for you to buy from them then it was last year?

There is a restaurant  I like to eat at and the owner always asks as Im leaving,what could we have done differently or better to improve your dining experience today?With almost every customer, every day, he asks for feedback to understand how to get better.

Are you this close to your customers after they tried the special?

Need help creating a loop with your customers?Connect with me hereand lets talk.

By Rube Goldberg (an old comic book) [Public domain], via Wikimedia Commons

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Startup success can be engineered by following the process, which means it can be learned, which means it can be taught.

The Lean Startup provides a scientific approach to creating and managing startups and get a desired product to customers hands faster. The Lean Startup method teaches you how to drive a startup-how to steer, when to turn, and when to persevere-and grow a business with maximum acceleration. It is a principled approach to new product development.

Too many startups begin with an idea for a product that they think people want. They then spend months, sometimes years, perfecting that product without ever showing the product, even in a very rudimentary form, to the prospective customer. When they fail to reach broad uptake from customers, it is often because they never spoke to prospective customers and determined whether or not the product was interesting. When customers ultimately communicate, through their indifference, that they dont care about the idea, the startup fails.

The Lean Startup method teaches you how to drive a startup-how to steer, when to turn, and when to persevere-and grow a business with maximum acceleration.

Using the Lean Startup approach, companies can create order not chaos by providing tools to test a vision continuously.

By the time that product is ready to be distributed widely, it will already have established customers.

The lack of a tailored management process has led many a start-up or, as Ries terms them, a human institution designed to create a new product or service under conditions of extreme uncertainty, to abandon all process. They take a just do it approach that avoids all forms of management. But this is not the only option. Using the Lean Startup approach, companies can create order not chaos by providing tools to test a vision continuously. Lean isnt simply about spending less money. Lean isnt just about failing fast, failing cheap. It is about putting a process, a methodology around the development of a product.

The Lean Startup methodology has as a premise that every startup is a grand experiment that attempts to answer a question. The question is not Can this product be built? Instead, the questions are Should this product be built? and Can we build a sustainable business around this set of products and services? This experiment is more than just theoretical inquiry; it is a first product. If it is successful, it allows a manager to get started with his or her campaign: enlisting early adopters, adding employees to each further experiment or iteration, and eventually starting to build a product. By the time that product is ready to be distributed widely, it will already have established customers. It will have solved real problems and offer detailed specifications for what needs to be built.

A core component of Lean Startup methodology is the build-measure-learn feedback loop. The first step is figuring out the problem that needs to be solved and then developing a minimum viable product (MVP) to begin the process of learning as quickly as possible. Once the MVP is established, a startup can work on tuning the engine. This will involve measurement and learning and must include actionable metrics that can demonstrate cause and effect question.

The startup will also utilize an investigative development method called the Five Whys-asking simple questions to study and solve problems along the way. When this process of measuring and learning is done correctly, it will be clear that a company is either moving the drivers of the business model or not. If not, it is a sign that it is time to pivot or make a structural course correction to test a new fundamental hypothesis about the product, strategy and engine of growth.

Progress in manufacturing is measured by the production of high quality goods. The unit of progress for Lean Startups is validated learning-a rigorous method for demonstrating progress when one is embedded in the soil of extreme uncertainty. Once entrepreneurs embrace validated learning, the development process can shrink substantially. When you focus on figuring the right thing to build-the thing customers want and will pay for-you need not spend months waiting for a product beta launch to change the companys direction. Instead, entrepreneurs can adapt their plans incrementally, inch by inch, minute by minute.

Progress in manufacturing is measured by the production of high quality goods. The unit of progress for Lean Startups is validated learning-a rigorous method for demonstrating progress when one is embedded in the soil of extreme uncertainty.

You dont have to work in a garage to be in a startup.Read More

A startup is an institution, not just a product, so it requires management, a new kind of management specifically geared to its context.Read More

Startups exist not to make stuff, make money, or serve customers. They exist to learn how to build a sustainable business. This learning can be validated scientifically, by running experiments that allow us to test each element of our vision.Read More

To improve entrepreneurial outcomes, and to hold entrepreneurs accountable, we need to focus on the boring stuff: how to measure progress, how to setup milestones, how to prioritize work. This requires a new kind of accounting, specific to startups.Read More

The fundamental activity of a startup is to turn ideas into products, measure how customers respond, and then learn whether to pivot or persevere. All successful startup processes should be geared to accelerate that feedback loop.Read More

Elements of a Feedback Loop

Paul Andersen defines the major elements of feedback loops. The receptors and effectors both sense and respond to changes in their environment. The following examples are used to illustrate the importance of feedback loops in maintaining homeostasis: speed signs, thermostats, thermoregulation, and blood glucose maintenance.

NGSS – Next Generation Science Standards

Im the creator spotlight in the. Thanks!

Full VR experience with the kids in Hong Kong today. Not skeptical anymore. Amazing!