Positive Feedback
Engineering definition
- The return of all or some of the output of a system or process to the input, which leads to instability. A familiar example is the loud squealing or howling sound produced by audio feedback in public address systems: the microphone picks up sound from its own loudspeakers, amplifies it, and sends it through the speakers again.
- In digital electronics, the forcing of voltages away from intermediate voltages into ‘0’ and ‘1’ states. “Thermal runaway” is uncontrolled positive feedback in which the heat of the current passing through the circuit allows more current to pass, heating the circuit further; this feedback loop can destroy semiconductor junctions.
- The release of heat in chemical reactions that can then increase the rate of reactions. Thermal runaway becomes possible, and in some cases can lead to explosions. This is a key issue in battery safety.
- In mechanical design, the process that causes tipping point, or “over-center,” mechanisms to snap into an open or closed position, e.g., in switches and locking pliers.
- The out-of-control absorption of more energy than an object can dissipate. This can cause collapse, as with the Tacoma Narrows Bridge in 1940.
Medical definition
- The enhancement of the original stimulus by the output. For example, during labor, a hormone called oxytocin is released that intensifies and speeds up contractions. This increase in contractions causes more oxytocin to be released, and the cycle continues on until the baby is born. Birth ends the release of oxytocin and the positive-feedback mechanism.
- The process of blood clotting, during which platelets cling to the site of an injured blood vessel and release chemicals that attract more platelets. The platelets continue to pile up and release chemicals until a clot is formed.
Confusion
As described, there are a variety of meanings associated with feedback across specialties in both the engineering and medical fields. Although the general meaning is the same for both medical and engineering professionals, the context in which the feedback is applied and the information that is fed back differ. An awareness of these differences is advised for both medical and engineering professionals.
