tgδ
In-series model
tgδ
Constant dielectric loss
Actual tested article
In-parallel model
f
f
Low frequency dielectric
High frequency dielectric loss curve
loss curve (<1kHz)
or low frequency circuit resonance
2. Relationship between frequency and dielectric loss
The dielectric loss can be divided into two ideal models: RC in series and
RC in parallel: RC in series tgδ=2πfRC; RC in parallel tgδ=1/(2πfRC). tgδ is in
a direct or inverse ration as the frequency f varies. As shown in diagram, f
makes a great influence on both complete direct ratio model and complete
inverse ratio model. However, the actual capacitor is in mixed model
composed by various models and influence of f turns to be smaller under this
circumstance.
3. Automatic variable frequency and 50Hz equivalent
The instrument takes two measurement points by two sides of
interference frequency 50 Hz with the method of automatic variable frequency
and then calculates the data under 50 Hz frequency on the basis. No single
medium of tested article will induce energy absorption peak under low
frequency, leaving out low frequency resonance in multiple-component circuit.
Besides, the dielectric loss closing to power frequency will vary monotonously
with frequency. Therefore, this kind of measurement will not cause any obvious
errors. Actually, the two dielectric loss values have little difference before
averaging, so they are of valuable reference in spite of their uneven values.
Currently, variable frequency dielectric loss tester has become a conventional
instrument for dielectric loss measurement with its excellent anti-interference
capacity and well-recognized accuracy.
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