Questions concerning thermistors

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Discussion Overview

The discussion revolves around thermistors, focusing on their resistance values, the significance of the b-constant, and their application in temperature-actuated circuits. Participants explore the use of amplifiers versus direct connections in circuit designs involving thermistors.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification, Homework-related

Main Points Raised

  • One participant questions the meaning of the single resistance value found on thermistor spec sheets and inquires about the b-constant.
  • Another participant suggests that most applications utilize the change in resistance with temperature (dR/dT) to drive a differential amplifier for proportional control or to use a voltage drop with a comparator for on-off control.
  • A participant expresses a preference for a simple on-off control mechanism.
  • There is a recommendation to refer to a national semi analog circuits handbook for examples and circuit designs, as well as a mention of circuit design handbooks available at Radio Shack.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the best approach for using thermistors in circuits, as different methods and preferences are expressed.

Contextual Notes

The discussion does not clarify the assumptions behind the use of amplifiers or comparators, nor does it resolve the specifics of the b-constant or its implications for circuit design.

Who May Find This Useful

Individuals interested in circuit design, particularly those working with temperature sensors and control systems, may find this discussion relevant.

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I've got some rather simple questions concerning thermistors. First, in viewing spec. sheets I only see one resistance value. What is that value telling me? In some of the specs there is something called a b-constant. What is that? Does a temperature actuated circuit demand an amplifier to take the small changes in resistance and produce larger voltage fluctuations? or can you just use them directly in series with a zener to make a temperature actuated switch? Basically I know little more than the general idea that they vary their resistance with temperature. Any answers, information, etc. would be much appreciated. Thanx for your time and patience with my ignorance.
 
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Most applications use the dR/dT----> dV/dT about a nominal value to drive a differential amp for proportional control, Or use the voltage drop and a windowed comparitor w/hystrerisis for on-off type control.
 
Yea, all I need is an on-off type deal.
 
If you have access to an national semi analog circuits handbook, there is a lot of good examples, otherwise, radio shack sells these small and really nice, circuit design handbooks, I think op-amps and comparators are in the same book, good designs that work and can be built quickly.
 

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