6.4 Fixture Compensation
AT3600 tester fixture compensation is equivalent to short-circuit and open-circuit correction on a component analyzer. It eliminates errors due to stray parasitic components on the fixture board itself. These are usually a combination of parallel capacitance between adjacent wires and sockets or pins, and series resistance and inductance along the lengths of wires.
Not all test programs require fixture compensation; and for some programs containing only high power tests, fixture compensation is not possible. As suggested in Chapter 3, it is best to try fixture compensation when performing trial runs on the program as it is being developed. If fixture compensation changes the test results, then it should be applied whenever the program is run in a production situation.
In production test, for optimum accuracy, fixture compensation measurements should be made :-
- Whenever the test fixture is changed.
- At the beginning of each day or work period.
- Whenever a new test program is loaded into the AT for execution
After you have pressed the COMPENSATE soft-key on the front panel, the tester will automatically perform all the compensation measurements and retain the results in internal memory. The compensation factors will then be applied to each transformer as it is tested.
For compensation, first make up a transformer bobbin with shorting links in place of the windings:
To make a shorting bobbin, solder short pieces of wire across the relevant pins of an otherwise blank bobbin. Do not use a bobbin that contains any transformer windings to make up a compensation test part, since this would invalidate the open circuit measurements.
Ensure that DC Bias current is switched off before connecting and disconnecting component under test.
After you have entered the name of a program where compensation can be applied, at the next display:
- Fit the shorting bobbin into the test fixture on the tester.
- Press the COMPENSATE soft-key.
The tester will perform the short and open circuit compensation.
As the compensation measurements are being made, the display will briefly show:
The tester will then show:
COMPENSATION PASS AND FAIL INDICATIONS
In the event of a failure check the following:
- The short circuit connections (if applicable)
- The fixture integrity.
And then retry the compensation.
If desired the test programs can be run without fixture compensation being performed, however this may affect the accuracy of the results, depending upon the type of transformer being tested and the fixture design.