Suresh, your response tends to suggest you do not understand the basics - go back and READ the datasheet on the DAC. Put simply, the output of the first op-amp is a VOLTAGE! You would have noticed this if you had done some basic investigation. What would this voltage be? Read the datasheet on the DAC!

The load the OPA547 presents to U4a is miniscule. A quick browse for the specs on the opa547 tells us that it is a high voltage, high current op-amp. The output current is good for 500mA.


Simply put, that part of the circuit would seem to vary the amount of and the polarity of the current applied to (what I assume) to be a relay under test. Through the mosfet, we can switch the current on/off at a rate determined by the 8254 - what this rate is is determined by the software. The software can measure the amount of actual current applied via the ADC. The software ,I expect, would have a tolerance band that it would test this current to in order to pass or fail the unit under test.

What I can't see is how it determines if the relay under test contacts have opened/closed.

So, if you wanted to test the minumum current in both polarities at which a relay operated, then this circuit would seem to fit the bill.

Can you tell us what the range of current for the relay under test is? How about the expected range of ADC values for the range of current? If you cannot answer these basic questions, how do you expect you would design a circuit? This is first year engineering stuff.