Problems on Transformer/LT coil evaluation

Abstracted from Agilent Effective Transformer/LF Coil TestingApplication Note 1305-3
Transformers and LF coils are used in power supplies, digital networks (forexample, ADSL) and various communication instruments to step up (or down)an AC voltage or for impedance conversion or filtering purposes. Thoughproduction of transformers is increasing year after year, there are problems thatQA test efficiency and production test throughput cannot be easily improvedbecause several different measurement instruments and setups need to be usedfor testing various transformer parameters. This application note introduces thecost-effective solutions to the transformer parameter measurements by usingthe Agilent 4263B LCR Meter.

Current Problems onTransformer/LF CoilEvaluation
The primary parameters that need to be known for transformer/LF coils areself-inductance, dc resistance, turns ratio and inter-winding capacitance.Conventional low-cost LCR meters have the following shortcomings when usedfor transformer/LF coil evaluation.

1. DC resistance of primary and secondary windings cannot be measured withLCR meters. (The DC resistance measurement requires using a separate testinstrument such as a multimeter.)

2. The turns ratio, a key transformer parameter, cannot be measured with LCRmeters.

3. The transformer parameters cannot be measured at 100 kHz because manylow-cost LCR meters do not cover high frequencies up to 100 kHz.

4. The test signal level is automatically selected according to the measurementrange, the test signal level cannot be user-defined for a specified level.

5. Total test throughput on production lines cannot be maximized because ofslow measurement
speed.

6. The connections of a transformer to the instrument (test fixture) must bechanged to measure parameters for the primary and secondary windings.The required connection changes make it difficult to enhance themeasurement efficiency.

To read more about solutions from Agilent.