3.3.13 Programming Hints And Tips
The following is a list of points that should be remembered when you are creating your test programs.
- Create your schematic first.
When you are creating your test programs, you should work in the following order:
- Initially, create the schematic.
- Then, set up the program options.
- Finally, create the list of tests that make up the program.
Note: If you make any changes to the schematic after you have created the list of
tests, then some tests may be inadvertently deleted. Examples where this may
happen are: deleting a winding or a terminal, and renaming a terminal.
- Use the recommended order for the tests in the program.
The actual tests used in the program are of course dependent on the type of transformer to be tested, and the number of parameters you have chosen to test. However, it is recommended that you generally do the tests in the following order:
To detect a transformer not correctly plugged into the test fixture, and any open circuit windings.
- b. Primary inductance or magnetizing current
To detect faulty core material, and the wrong number of primary turns.
- Turns ratios or open circuit voltages
To detect any windings with the wrong number of turns.
- Isolation tests such as Insulation Resistance
To detect poor interwinding isolation where safety is not an issue, for example between two secondary windings.
- Safety tests such as Hi-Pot
To detect poor interwinding isolation; but this time where safety is an issue, for example, from a primary winding to a secondary winding on a mains isolation transformer.
In the above list, items b and c will depend on the type of transformer: For ferrite cored transformers operating at frequencies higher than 1kHz, it is preferable to measure the primary inductance and the turns ratios between windings.
For iron cored transformers operating at the 50 or 60Hz line frequency, where normal operation extends to the point of core saturation, magnetizing current and open circuit voltage measurement are normally the preferred tests.
- Use test limits which are as wide as possible.
For example, if you are testing the turns ratio between windings where the actual number of turns on one of the windings is only 10, specify limits of ± 5% (which is equivalent to half a turn).
- Make use of the Measure button.
For many tests, the dialogue box for the test contains a button labeled ‘Measure’.
If, when you are creating your test program, you have a tester connected to your PC, fitted with the appropriate test fixture containing a specimen transformer, clicking on the Measure button will signal the tester to measure the actual parameter of the test. The result will be returned to the PC, and the Editor will insert it as the ‘nominal value’ in the limits section of the test dialogue box.
This is often the best way to find the value for some of the parameters which you may wish to test, but which do not appear on the actual transformer design documents.
- User Offset.
Under most circumstances, performing compensation as described earlier will compensate all measurements for the effects of stray parallel and series impedances, providing accurate measurements upon the part under test.
If compensation cannot be performed conveniently or an offset is required in the measurement is required for other reasons, then enable ‘User Offset’ and enter the value to add to the result.
Enter a negative value to subtract from the measured result. The adjusted result (including any offset) is the result that will be used to provide PASS / FAIL judgments, and is the result that will be printed and / or stored by the server.
- Finally, download and run the program from the Editor, to make sure the results are what you expect, before you use it in production.