Hi,
I have a AD594 IC in my school's instrumentation laboratory. I want to test its offset voltage.
We know from its datasheet that AD594 has an input offset voltage about 16 micro volt and its gain equals with 193.4. So, I should read 3.1 mv from its output (pin 9 connected with 8) when I have connected its 1st, 4th and 14th pins together. In the other words, when I make zero its input potantial difference, I should read 3.1 mv by any voltmeter at pin 8 (the IC,s output). But I read a voltage about 256 mv from its output in practice!!!

Now my question is:
- How can this be possible?
- Is there any points about how to use this IC?
- Can anyone draw the schematic of the circuit, here?

I'd be very appreciated if anyone can help me.

 

Have you read the data sheet and know as well as understand the purpose of this chip? Shorting pins 1 and 14 using a short copper jumper the chip should output a voltage equivalent to ambient temperature for a Type K thermocouple. Better yet place a Type K thermocouple in the circuit and use the chip as designed. Read the data sheet and understand exactly what this chip is designed for. Find a Type K Thermocouple chart and understand the mv outputs and what CJC actually is. The offset voltage you mention is all a part of understanding CJC.

Ron

 

Have you read the data sheet and know as well as understand the purpose of this chip? Shorting pins 1 and 14 using a short copper jumper the chip should output a voltage equivalent to ambient temperature for a Type K thermocouple. Better yet place a Type K thermocouple in the circuit and use the chip as designed. Read the data sheet and understand exactly what this chip is designed for. Find a Type K Thermocouple chart and understand the mv outputs and what CJC actually is. The offset voltage you mention is all a part of understanding CJC.

Ron

Many thanks for your response
Actually measuring this offset voltage is part of our instruction book and we are expected to obtain this voltage as a part of our work in the laboratory.
When I connect a thermocouple instead of shorting pins 1 and 14, I couldn't read a voltage which is compatible with the datasheet's. I was wondering if I have to use the other pins of the IC- especially the pins which are related to the compensator unit.

 

Circuit here, note the 16uV is for J type thermocouples. Just out of curiosity, when you finally measure the voltage, what are you going to do with it?, it doesn't make any difference to your design, it will give 10mV per degC at pin9, like it's designed to do!

 

Connect it as per Doggydave's drawing. With a TC attached you should read 10 mV per degree C of ambient air temperature (TC Temperature). You also shopuld have mentioned this was a school work assignment.

Ron

 

Circuit here, note the 16uV is for J type thermocouples. Just out of curiosity, when you finally measure the voltage, what are you going to do with it?, it doesn't make any difference to your design, it will give 10mV per degC at pin9, like it's designed to do!

View attachment 126678

Thank you very much... It's just a school work assignment.