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Where Used

The DC resistance match test – as opposed to an ordinary DC resistance measurement (R) - is used on audio and telecommunications transformers, where it is important that the resistance of different pairs of windings is controlled and matched to a specified ratio. The absolute value of the resistances may be of less importance to the performance of the transformer than the match between two resistances.

Measurement Conditions

To measure DC resistance match, the tester makes two DC resistance measurements (see the R test) and compares the two results. Limits for the match of the two measured resistances may be set in terms of the ratio between them (e.g. 1:1 ± 5%).

By adding further DC resistance match tests to the test program, any number of DC resistances can be tested for match.

Choosing Test Conditions

For optimum accuracy and performance, use the test conditions shown in the DC resistance section of this chapter for each of the two windings.

Programming the Test Using the PC Test Editor

• Select the integration time required.
• Enter the terminal names between which the X resistance is to be measured.
• Enter the terminal names between which the Y resistance is to be measured.
• Set the specific resistance for both X and Y terminals, and then set the negative and positive percentage (%) limits.
• Select OK. The test specification will now be displayed in the program window.

Use the PC Editor's 'Measure' button (together with a sample part) if you are unsure of how to choose the test conditions.

Choosing Test Limits

The test limits are the specific resistances for both X and Y terminals together with + and – percentage limits.

Use the PC Editor’s ‘Measure’ button (together with a sample part) if you are unsure of the resistance values.