Cheap solution to read temp. on analog in?

Icefire · Mar 27, 2007

Any way to read a thermistor/thermocouple on a GE 90 Micro Analog Input?
0-10V, 0-20mA or 4-20mA?

I tryed with a LM35DZ chip which give 10mV/*C, too sensible/not enought resolution.. since the PLC resolution is 10mV.

I want to read around 60-90F

Lancie1 · Mar 27, 2007

Icefire,

Buy a thermocouple 4-20 miliamp transmitter for thermocouple input to any PLC analog input, available from many places, including Omega.com for $99. A TX91A-J2 would read 0 to 200 degrees F from a Type J thermocouple. What type of thermocouple are you using?

http://www.omega.com/ppt/pptsc.asp?ref=TX91A_92A&Nav=temn03

Tom Jenkins · Mar 27, 2007

We've had great results with the Dill Intruments sensors - outputs that are direct voltage and 4-20 mA are available.
http://www.dillinstruments.com/

Icefire · Mar 27, 2007

TConnolly · Mar 28, 2007

http://www.ifmefector.com/ifmus/web/padv0!2_40_10_10.html

Available with 4-20mA or 10vdc outputs.

agarb · Mar 28, 2007

Icefire said:
Any way to read a thermistor/thermocouple on a GE 90 Micro Analog Input?
0-10V, 0-20mA or 4-20mA?

I tryed with a LM35DZ chip which give 10mV/*C, too sensible/not enought resolution.. since the PLC resolution is 10mV.

I want to read around 60-90F

How much more resolution do you need? If you use an LM34 in place of the LM35 you will get 1.8 times better resolution. An LM34 will give you 10mV per degree Farenheit instead of the 10mV per degree Celsius that you get with the LM35. So 60-90F gives you 600-900mV instead of 150-320mV.

Icefire · Mar 28, 2007

I was using a LM324 With a non-inverting gain of 10, I got 2.546 volts but the PLC's value fluctuate +-0.2V.

Maybe something with the analog input..

It's a GE 90 Micro

agarb · Mar 28, 2007

Icefire said:
I was using a LM324 With a non-inverting gain of 10, I got 2.546 volts but the PLC's value fluctuate +-0.2V.

Maybe something with the analog input..

It's a GE 90 Micro

Add a low pass filter; either RC or use a spare op-amp in the LM324?

Or even filter it in in the PLC?

keithkyll · Mar 28, 2007

Make sure the LM324 and the PLC share the same ground reference.

jvdcande · Mar 29, 2007

Icefire said:
I was using a LM324 With a non-inverting gain of 10, I got 2.546 volts but the PLC's value fluctuate +-0.2V.

Maybe something with the analog input..

It's a GE 90 Micro

What's the distance from sensor to PLC? And were did you place the LM324?

Kind regards,

Icefire · Mar 29, 2007

the circuit was on 2 feet from the plc on a pratice breadboard.

I think it has something to do with the inner values of the PLC.

The A/D can be calibrated.

Cheap solution to read temp. on analog in?

Icefire

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Lancie1

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Tom Jenkins

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Icefire

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TConnolly

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