3.3.12 Fixture Compensation
Often when measuring small values of resistance, inductance or capacitance, the effects of the fixture can add significant errors to the results. To allow you to make more accurate measurements, the AT Series Testers have built-in firmware to compensate for the fixture parasitics.
If fixture compensation is required, follow steps 1, 2 and 4 of the procedure in section 3.10 of this chapter, so that the tester is connected and the program is downloaded.
Then from the top-level menu bar, select:
If your program does not contain any tests where compensation can be applied, you will see the following message:
When you click on ‘OK’ to return to the top level menu, the tester will not make any measurements.
Most programs will contain at least one test where fixture compensation can be applied. In this case, you will then see one of two messages:
At this point you should ensure that the appropriate fixture has been placed on the tester. With the first message, it is possible to leave the fixture empty.
The second message will be displayed when the program contains at least one test for which short-circuit compensation is applicable. As the program may also contain tests requiring open-circuit compensation, you should ideally plug a dummy header into the fixture, where all the transformer windings are replaced by short-circuit links.
After you have clicked on the ‘OK’ button at either of the messages, the tester will be commanded to make the compensation measurements for your test program.
If errors are encountered, such as a shorting link is not fitted, the editor will display the appropriate warning message, and allow you either to try again, or to cancel the compensation.
When the compensation measurements have been successfully completed, the compensation values for each test in the program will be stored inside the tester. Any subsequent measurements (started as described above by clicking on Tester - Run Program) will return compensated results to the Editor.
If you are not sure whether to compensate or not, simply try it. If any of the results change significantly, then it should be done.
REMEMBER: Whenever you make changes to the program, the compensation results in the tester will no longer be valid.
Make sure to compensate again each time you download a test program to an AT Series Tester, whether the program has changed or not.