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AD594AQ Troubleshooting

Question asked by dbaron on Jan 29, 2014
Latest reply on Jan 31, 2014 by dbaron



I have been working on a circuit using the AD594AQ to amplify the signal from a J type thermocouple.  I have two of these circuits, each experiencing different problems.  I have attached the schematic that I am using for both circuits.  They are currently on breadboards.


Circuit 1: This circuit is giving readings between pin 9 and ground, and is very accurate between 0 degrees Celsius and 25 degrees Celsius.  Anything above 25 degrees, however, the readings from pin 9 are too low.  At 35 degrees Celsius, the readings are about 80 mV off, and at higher temperatures, the readings are hundreds of mV off.  As the thermocouple will mostly be reading high temperatures, this is problematic. 


Circuit 2:  This circuit is not giving correct readings off of pin 9. The voltage across the power supply (the 9V battery and 10K resistor in series) is 9.25V while disconnected from the circuit, however, when power is connected to the circuit, there is a reading of 2.85V across pins 4 and 11, as well as pin 9 and ground.  I checked all of the wiring, and there are no incorrect connects in regards to the schematic I have attached, I am guessing that there may be a broken wire somewhere, but I'm not sure where to look in the circuit, any help in finding where this reading may be coming from would be very helpful.


Thank you