LM392 Dual Comparator Circuit for Accurate Real-Time Temperature Differential Sensing

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Request for LM392 improvements and reference material
#1 21662165 15 May 2012 16:04

Tony Matteo Tony Matteo

Anonymous

Request for LM392 improvements and reference material
Post #1 21662165 15 May 2012 16:04

Hello I lost my way and hoping you may guide me back.
I will appreciate you expert time and advice. it will be put to very good use. I started this project a few years back with the main gold of accuracy, 0.5F or better. I have selected 1wire family project as my final gold. In achieving 8 eight sensor location at one object, detecting .025F between any relationship, as well as 4 four sensor locations, and 3 sensor locations. That being said, Right now Im using LM932N, and my gold is 2 two sensors comparison differential, Using 2 thermistors on one location, I would like to have you suggestions to this circuit improvements to LM392 to choice from, any reference material I can refer to. I did pick this out but have problems understanding what and why. Thank You for you Input

All The Best
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#2 21662166 16 May 2012 01:01

Frank Bushnell Frank Bushnell

Anonymous

Post #2
21662166 16 May 2012 01:01

What are you measuring the temperature of ?
What is the data to be used for ?
Can you post the general circuit design you have produced so far ?
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PNP 2N4403 replaces 2N2222 and 100 kΩ removed
#3 21662167 16 May 2012 09:46

Tony Matteo Tony Matteo

Anonymous

PNP 2N4403 replaces 2N2222 and 100 kΩ removed
Post #3 21662167 16 May 2012 09:46

Mr Bushnell, Thank you for your interest. Temperature of ? > many surfaces = liquid, air, metals, and skin.
Data used for ? > again many = some materials may work there best displacing limited amounts of temperature, alerting on there relationship to limits of work the perform will lead to performance efficiency. As skin produces heat or lack of in a range of difference may indicate an early indicator to watch. At this point it is the data gathering it its simplest accurate form.

I enclosed file
Changed NPN 2N2222 to PNP 2N4403 and removed 100K @ 5 to Ground,

Thank You
All The Best
#4 21662168 16 May 2012 11:36

Frank Bushnell Frank Bushnell

Anonymous

Post #4
21662168 16 May 2012 11:36

Hi again, my computer cannot figure out what application to open your file with ! Can you let me know ? Thanks !
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#5 21662169 17 May 2012 15:21

Tony Matteo Tony Matteo

Anonymous

Post #5
21662169 17 May 2012 15:21

Very Sorry Inclosed wil be a pdf

Thant for you patients
Pin 4 grounding and nulling pot bias suggestion
#6 21662170 17 May 2012 18:00

Frank Bushnell Frank Bushnell

Anonymous

Pin 4 grounding and nulling pot bias suggestion
Post #6 21662170 17 May 2012 18:00

I think pin 4 needs to go directly to ground, as it is the ground for the IC's power supply.
When the two sensors are at the same temperature, the output from the op-amp will be indeterminate.
The nulling pot on pin 2 may need to be between two equal resistors to provide an intermediate voltage level. (1/2 Vcc ?)
Rather than just a comparator giving an on/off, it may be more useful to have an output that is proportional to the temperature difference that is sensed, perhaps to drive a display showing the magnitude of the temperature difference..
I am not very hot on temperature sensing, so anyone else who has any ideas is welcome to chip in.
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Request for simpler explanation of LM392 external parts
#7 21662171 19 May 2012 17:46

Tony Matteo Tony Matteo

Anonymous

Request for simpler explanation of LM392 external parts
Post #7 21662171 19 May 2012 17:46

Thank You for you information it is Very helpful a display would be excellent. I choose this IC believing it is a good choice at the time 4 yrs ago I have since gotten a little lost in understanding my circuit.

Im hoping you will comment on my over all solution. circuits are in excellent range -10>85 c or -55>125c with .05 accurate are excellent. Working Range for accuracy range of work in ( -5 > 5 C ) .5 or better accurate. set point of floating differential (-8.33c ) (17f ) in increments (.3c) (.5f) alerting each way. What would benefit my solution to construct a solution is the source of information how the chips external parts effect works to evaluate the out put. more straight forward than technical. Any suggestions or directions will be very helpful.

Thank You
All The Best
#8 21662172 25 May 2012 11:34

Tony Matteo Tony Matteo

Anonymous

Post #8
21662172 25 May 2012 11:34

EVERYTHING you need to know operational Amplifiers

http://openbookproject.net/electricCircuits/Semi/SEMI_8.html#xtocid72750

Link Tested

Excellent Reference
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Topic summary

The discussion centers on designing an accurate real-time temperature differential sensing circuit using the LM392 dual comparator IC, targeting a precision of 0.5°F or better. The project involves comparing two thermistors at a single location to detect minute temperature differences as low as 0.025°F across multiple sensor arrays (up to eight sensors). The temperature measurements cover various surfaces including liquids, air, metals, and skin, with applications in performance efficiency monitoring and early heat-related indicators. Circuit improvements suggested include proper grounding of pin 4 on the LM392, adjusting the nulling potentiometer to provide an intermediate voltage (around half Vcc) for stable output, and considering an output proportional to temperature difference rather than a simple comparator on/off signal. The author seeks clearer, practical explanations of how external components affect the LM392 output to enhance understanding and circuit accuracy within a working range of -5°C to 5°C. Reference material on operational amplifiers was recommended to aid comprehension of the IC’s behavior and design considerations.
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LM392 Dual Comparator Circuit for Accurate Real-Time Temperature Differential Sensing

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Topic summary