measure a choke with lcr meter

[Hermes Rozsa]

Hello colleagues,
I need your guidance and criteria.
I must measure a choke. The manufacture's specifications are as follows:
"The inductance Shall be 7.5 mH +-10% when subject to 4A AC of 50 Hz on the winding."

For the measurement I have an LCR meter, the 4310 Wayne Kerr. When performing measurement I get values bellow 20% predicted in the specifications.

Awaiting your comments and grateful for your attention.
Hermes

 

[erikl]

Show your measurement setup!

 

[Warpspeed]

The difficulty here is that powdered iron toroids increase their effective permeability when excited with a high enough current.
Just trying to measure the inductance the normal way will probably show less, than when it is four amps of mains current flowing through it.
The reason is the "S" shape of the BH curve. The slope is greater in the middle than at either end.

**broken link removed**

 

[D.A.(Tony)Stewart]

If chokes are selected to reduce pulsed %THD and ripple then you must use pulse mode to test equivalent value at rated current to see if it meets design requirements.

If you want to verify part value against Mfg specs, then it must be tested in same method using same; f, current source, DC bias.

Correlation between the two methods depends on design for time and frequency method.

 

[Hermes Rozsa]

test 2 V DC Bias:Int Freq:50Hz

7.5

RC475ELC-1

Ls Rs Qs As Zs
19% 6.055 mH 348.67 mΩ 5.048 78.79 ° 1.93 mΩ

Lp Rp Qp Ap Zp
17% 6.25 mH 10.75 mΩ 9.09 -83.72 ° 1.93 mΩ

RC475ELC-2

Ls Rs Qs As Zs
19% 6.049 mH 345.26 mΩ 5.036 78.76 ° 1.93 mΩ

Lp Rp Qp Ap Zp
17% 6.25 mH 10.75 mΩ 9.07 -83.7 ° 1.93 mΩ

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measurement setup

 

[FvM]

What's the maximal DC bias current generated by the LCR meter? I guess something in the 10 mA range.

Quite obviously, it's impossible to achieve test conditions similar to the specicifications in post #1 with a regular LCR meter. Just forget it!

IAC of 4A/50Hz is a large signal measurement, LCR meters do small signal measurements. A straigthforwrd measurement setup uses a 50 Hz AC source (e.g. a transformer), a rheostat and a multimeter or oscilloscope and calculates the inductance from voltage measurements, using respective AC network relations.

 

[D.A.(Tony)Stewart]

The report shows 2Vdc with Rs = 348.67 mΩ So Idc=>5.7Adc. You can choose 1 or 2Vdc or use external Vcc. Check reverse polarity due to Remnance.

Normally AC chokes are tested at rated current and f while DC chokes are rated at 10% L drop at rated DC current.

Meanwhile L testers for sine at high currents use a current source for AC at high currents if necessary. Your unit is programmable in small steps up to 2Vac, impedance must be computed internally by phase shift and current sensing.

100mΩ Approaches the lower accuracy limits of ~10% according to the datasheet. Check.

You may decide on your application if it more appropriate to test 1V dc or not , with ramp up to 2Vac to check linearity.

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The Q(f) , loss tangent(f), self resonant frequency,SRF,Phase Shift(f), Damping factor (f) and Dissipation Factors (f) are all related. Where the last two are similar impedance ratios of Rs/X(f) but normally applied to inductor and caps respectively. Chokes reduce with increasing current near saturation and some caps reduce C with rising V due to ceramic dielectric properties.

What kind of inductor or reactor is this?

explain RC475-ELC-1,-2

 

[FvM]

The report shows 2Vdc with Rs = 348.67 mΩ So Idc=>5.7Adc. You can choose 1 or 2Vdc or use external Vcc. Check reverse polarity due to Remnance.

The calculation would be correct if... 4110 user manal specifies 10 mA short circuit of the internal bias source.