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jpnorair

Thermistors!

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I discovered these things today (well, 9 May 14).

 

I used a pair of NTC thermistors with 100kOhm @ 25C, 1MOhm @ -20C, in the design of a battery protection circuit.  I've never used a thermistor before.  What have you done with a thermistor?  They are cheap and interesting... I like!

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Measuring temp (duh!) in equipment enclosures

 

Temp monitor for the regulator/charge controller on one of my bikes

 

LImited temp range tempco cancellation for fixed resistors (there are better ways for wide temp range, but none are cheaper)

 

Feedback device for a heated box (constant temp environment for a thermocouple cold junction and amp)

 

The possibilitiies are endless.....

 

When I am worried about accuracy, I do prefer, at slighty higher price, the integrated temp to current devices or direct digital output devices (like DS18B20), as they tend to be more stable and have tighter specs than thermistors.

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They're used in the 3d printers hot ends and heating beds.

 

In university we used them in wheatstone bridges, if I remember well, it allows the resistance to be approximated to a line. Lot less useful now that it's easy to have a values table in a microcontroller.

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airflow and airspeed indication.

 

eg: to make sure that a fan is cooling a piece of equipment.    so, using two thermistors:  one isolated from the airflow (reading ambient air temp), the other in the fan's airflow.   the two thermistors' resistance difference indicates that the fan properly cools the equipment.

 

i heard of an airspeed indicator that used two thermistors near heated elements.   again, one in the static air, the other in the moving air.  So here, the moving air cools the heated element, resulting in lower measured resistance than the other thermistor.

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airflow and airspeed indication.

 

eg: to make a fan is cooling a piece of equipment. so, using two thermistors: one isolated from the airflow (reading ambient air temp), the other in the fan's airflow. the two thermistor's resistance difference indicates that the fan properly cools theequipment.

 

i heard of an airspeed indicator that used two thermistors near heated elements. again, one in the static air, the other in the moving air. So here, the moving air cools the heated element, resulting in lwer measured resistance than the other thermistor.

I think that's the principle for the Mass Air Flow sensor in most modern cars' air intake.

edit: sort've, I think it works by a heated wire and thermistor and ECU changes duty of the heated wire to maintain constant temperature and duty reflects rate of thermal loss and therefore absolute mass of airflow.

 

Sent from my Galaxy Note II with Tapatalk 4

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el cheapo RF 'calorimetric' power measurement - measure the temperature (inferred from the resistance) of the thermistor in close thermal proximity to a resistive RF load.

 

 

temperature compensation of all sorts of stuff - but I guess you know about that ! :  oscillators (frequency and level); stabilizing light output from laser leds or incandescentlamps,    etc.

 

 

if you get some PTCs, that's another story.     like those  'resettable fuses''.    large PTCs were used for ages in electric power windows as a brute-force method to choke off the current when the motor drove the window full top  -or-   full bottom.

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temperature compensation of all sorts of stuff - but I guess you know about that ! :  oscillators (frequency and level); stabilizing light output from laser leds or incandescentlamps,    etc.

This is what is really fun for me, because it's possible to do a lot of these things with just two thermistors, an op-amp, and some other passives.  No MCU needed.  I love doing algorithms in analog... way back in 2003 I used to do a lot more, but for the most part it is so cheap and reliable to use digital logic now.

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I haven't used any myself, yet, but they are also used for automotive fuel injection intake air and coolant temperature sensors and many temperature gauges and for battery temperature / charge regulation and variable speed fan control in many cell site battery stacks and other cabinets.

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