IR Thermopile OpAmp - Electronic Circuits Projects Diagrams Free

binux369 · 7th October 2004, 06:32 AM

I research IR measurement temperature for my study minithesis to obtain engineer degree of university and I use IR thermopile
I have a standart thermopile detectore TO-5 Single-Channel Thin Film Based Thermopiles
I was tray use IC OP177 opamp prcesison integral n inverting but output in OP177 no ressponding.
can help me any design opamp for thermopile sensor.

thenks

Oznog · 7th October 2004, 07:18 AM

The thermopile I looked up has an output of 40uV/deg K. This requires an op amp with a very low input offset and your OP177 would be good for this with an offset of 25uV max @ 25C. BUT, your OP177 was designed and specified for +/- 15V operation, which is probably more than available in your circuit. In fact, the common mode range for this op amp does NOT include the V- supply, so if you use a 5V source and gnd the supply and thermopile at the V- terminal, the circuit will not operate.

Unless you have the +/- 15V available, you need to replace the OP177 with a similar low offset op amp specified for 5V operation (or maybe 12 if it is powered by a car or some larger supply) and be sure it also has low input noise. Also look for a high output voltage- many can only output 3V with a 5V supply, if it is specified as "Rail-To-Rail Output", it can give you 5V.

Correct me if I'm wrong, but the thermopile puts out a negative voltage if the target is colder than the thermopile, right? In that case, you'll need to make up a low noise bias point at 2.5V to act as a ground.

You still may need noise filtering, I expect that thermopile may be a noisy sensor. In that case, the op amp noise may not be an issue, you'd just use it as a preamp before the noise filter.

Be aware you MUST use the cold junction temperature to compensate the output. The signal itself is only the difference between the target's temp and the thermopile's temp.

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7th October 2004, 06:32 AM	(permalink)
binux369	IR Thermopile OpAmp I research IR measurement temperature for my study minithesis to obtain engineer degree of university and I use IR thermopile I have a standart thermopile detectore TO-5 Single-Channel Thin Film Based Thermopiles I was tray use IC OP177 opamp prcesison integral n inverting but output in OP177 no ressponding. can help me any design opamp for thermopile sensor. thenks __________________ i research ir thermopile for my study

7th October 2004, 07:18 AM	(permalink)
Oznog	The thermopile I looked up has an output of 40uV/deg K. This requires an op amp with a very low input offset and your OP177 would be good for this with an offset of 25uV max @ 25C. BUT, your OP177 was designed and specified for +/- 15V operation, which is probably more than available in your circuit. In fact, the common mode range for this op amp does NOT include the V- supply, so if you use a 5V source and gnd the supply and thermopile at the V- terminal, the circuit will not operate. Unless you have the +/- 15V available, you need to replace the OP177 with a similar low offset op amp specified for 5V operation (or maybe 12 if it is powered by a car or some larger supply) and be sure it also has low input noise. Also look for a high output voltage- many can only output 3V with a 5V supply, if it is specified as "Rail-To-Rail Output", it can give you 5V. Correct me if I'm wrong, but the thermopile puts out a negative voltage if the target is colder than the thermopile, right? In that case, you'll need to make up a low noise bias point at 2.5V to act as a ground. You still may need noise filtering, I expect that thermopile may be a noisy sensor. In that case, the op amp noise may not be an issue, you'd just use it as a preamp before the noise filter. Be aware you MUST use the cold junction temperature to compensate the output. The signal itself is only the difference between the target's temp and the thermopile's temp.