Design an circuit that measures a temperature differential and returns a 0-10K ohm resistance

Closed - This job posting has been filled and work has been completed.
Engineering & Architecture Product Design Posted 3 years ago


Hours to be determined
Less than 1 month

Start Date

December 4, 2012


Design (and optionally ship to Northern California) a device that meets the following conditions. I will use this with but need help with the EE side of things...

1) Provides two NTC thermistors on 60" leads. We shall call these temperature sensor A and sensor B.
2) Is intended to measure the temperatures within the range 30°C/86°F to 38°C/100.4°F. Please choose the thermistors carefully :)
3) Measures the relative temperature DIFFERENCE between sensor A and sensor B. The higher the difference, the higher the resistance from 0 to 10K ohms.
4) The sensitivity can be adjusted from 0.05°C to APPROXIMATELY 5°C using a trimpot. E.g., at the lowest setting, a 0.05ºC or higher difference registers as 10K, while at the highest setting a APPROXIMATELY 5ºC difference is required. What's important is the higher side of the sensitivity sensitivity; I imagine that the used range will almost always be <2°C.
4a) Bonus if the value of the trimpot itself can also be measured from 0-10K ohms
5) Assign all rights to the foregoing design (copyright/patent/etc) to myself and agree to execute a non-disclosure agreement upon commencement of the work.
6) The design can be assembled on a breadboard with readily available parts.
7) If you would like to assemble and ship the item (for an additional fee to be specified by the contractor), package it in a small case that does not need to be opened to adjust the trim pots.

Note that sensitivity over accuracy/reproducibility is the goal. It is not important that I can reliably state "Oh, I know the temperature differential is 1°C because I haven't touched the trim pots and it's at 5K ohm." Rather, I'm most interested in seeing relative changes in temperature between the two thermistors with the greatest (adjustable) accuracy. I don't need to know what the absolute temperatures are or even the absolute difference... the trimpot is there to calibrate the sensitivity and the difference would be measured over time.

In your bid, please specify a firm estimate for schematics that meet the above description. If you are willing to build and ship it for an additional fee, please advise what that is. You will be well treated! :)

Skills: design

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