East Tester ET4410&ET4510 Desktop LCR Meter

[mawyatt]

Thanks, found the 1657 manual and see the 0.047uF and inductor on the DUT+ P sense lead.

Seems that the DUT is current source driven and thus the sense line doesn't need to support any DC bias voltage and can be "blocked", however the current source needs to be able to support the entire DC bias range. Having such a high impedance on the +P line keeps the value of the DC blocking cap small, even at 0.047uF this placed the HP corner at ~1.6Hz.

If the stimulus lead and the sense lead both were AC coupled (DC blocked), then they should be able to support any external DC bias but suffer from the issue previous described.

Anyway, interesting stuff!

Best,

[nctnico]

Noted that Electrolytic Mode when reviewing the manual, wonder if this places a DC bias on the DUT that is equal to the peak AC voltage to keep DUT waveform from going negative?

Also wonder if the instrument places a series capacitor to remove the DC bias, or just uses analog techniques (subtraction) or digital to remove the DC bias?

Best,

I think you're right, this does simply put DC bias to prevent it from going negative. The voltage range of bias function is just sufficient for that.
But that function is already pretty good for very inexpensive instrument.

DC bias for capacitors is reason I kept my old 1657 Digibridge. That is otherwise not very remarkable instrument (it was in it's day, and still useful today) with very limited test frequencies(100Hz, 120Hz and 1kHz). But it officially supports external DC bias source, and it officially supports at least 30V.  Input capacitor is rated for 100V...

It works well for larger values.. It is not meant to be used for low pF ranges.. from some 100pF to 1000uF it has 0.2% accuracy...

If the LCR meter uses an internal series capacitor Cs to remove the DUT DC bias, and you are measuring a large value capacitor Cdut, how is the internal series capacitor Cs accounted for since the resultant capacitance "seen" by the measurement mechanism should be 1/(1/Cs + 1/Cdut)?

Is this by a lookup table and interpolation created during calibration, or maybe just calculate the Cdut from the measured value?

Edit: Reason I ask is because it seems the uncertainty in the Cdut measurement gets worse as Cdut gets larger WRT the series Cs value. A large Cdut WRT Cs means that most of the measurement voltage appears across Cs and not Cdut.

Most common LCR meters send an AC current through the DUT. Not a voltage. Subsequently the AC voltage is measured across the DUT. Using the phase and amplitude from the AC current and voltage, the various parameters for the DUT can be calculated. So in the end whatever is in series with the DUT gets cancelled out. You can also connect an external DC blocking capacitor in series and you'll still get good measurements. However, if you are getting near the limits of the LCR meter, you'll need to use good Kelvin leads (shielded) and calibrate them at the settings you are using in order to get accurate readings.

[2N3055]

Thanks, found the 1657 manual and see the 0.047uF and inductor on the DUT+ P sense lead.

Seems that the DUT is current source driven and thus the sense line doesn't need to support any DC bias voltage and can be "blocked", however the current source needs to be able to support the entire DC bias range. Having such a high impedance on the +P line keeps the value of the DC blocking cap small, even at 0.047uF this placed the HP corner at ~1.6Hz.

If the stimulus lead and the sense lead both were AC coupled (DC blocked), then they should be able to support any external DC bias but suffer from the issue previous described.

Anyway, interesting stuff!

Best,

Huh, on my schematic it says C60 is 0,47uF (470nF)...

One thing to note here: because of the way it is implemented, only DC bias voltage can be applied to DUT that has to be capacitor.
The DUT itself is DC block for low side terminals so voltage source cannot inject any DC current from I+ to I-/P-. There are protection diodes that will partially protect instrument in case you do something wrong, but measurements will be nonsensical and current range source resistors are in danger..

[mawyatt]

Huh, on my schematic it says C60 is 0,47uF (470nF)...

One thing to note here: because of the way it is implemented, only DC bias voltage can be applied to DUT that has to be capacitor.
The DUT itself is DC block for low side terminals so voltage source cannot inject any DC current from I+ to I-/P-. There are protection diodes that will partially protect instrument in case you do something wrong, but measurements will be nonsensical and current range source resistors are in danger..

The schematic I pulled up was a photo of the manual and very hard to read, so probably was 0.47uF not 0.047uF. This would place the corner at 0.16Hz, even better!!

Did note how the current was measured in the lower leg at virtual ground with transimpedance amp, and current supplied to DUT with what seemed to be just a series resistor on the top side. If so, this would place the DUT inside the current control loop rather than just forcing the current thru the DUT and measuring the voltage across the DUT.

Best,

[2N3055]

Huh, on my schematic it says C60 is 0,47uF (470nF)...

One thing to note here: because of the way it is implemented, only DC bias voltage can be applied to DUT that has to be capacitor.
The DUT itself is DC block for low side terminals so voltage source cannot inject any DC current from I+ to I-/P-. There are protection diodes that will partially protect instrument in case you do something wrong, but measurements will be nonsensical and current range source resistors are in danger..

The schematic I pulled up was a photo of the manual and very hard to read, so probably was 0.47uF not 0.047uF. This would place the corner at 0.16Hz, even better!!

Did note how the current was measured in the lower leg at virtual ground with transimpedance amp, and current supplied to DUT with what seemed to be just a series resistor on the top side. If so, this would place the DUT inside the current control loop rather than just forcing the current thru the DUT and measuring the voltage across the DUT.

Best,

Current is not regulated. There is 0,25V voltage source, source limiting resistor (10R, 1k, 100k) in upper leg (I+) going into DUT, and then over reference resistors (again 10R, 1k, 100k) into return path (GND). Measurement is strictly relative, between voltage/phase on DUT and reference resistor on lower leg (I- to GND).
It measures low impedances quite well. It has 20 Ohm source impedance (source+ref resistor) in its lowest range..

[mawyatt]

Most common LCR meters send an AC current through the DUT. Not a voltage. Subsequently the AC voltage is measured across the DUT. Using the phase and amplitude from the AC current and voltage, the various parameters for the DUT can be calculated. So in the end whatever is in series with the DUT gets cancelled out. You can also connect an external DC blocking capacitor in series and you'll still get good measurements. However, if you are getting near the limits of the LCR meter, you'll need to use good Kelvin leads (shielded) and calibrate them at the settings you are using in order to get accurate readings.

Yes agree about AC current use, BTW you can't "send a voltage thru a device", same as you can't "place a current on a device". The measured parameter is always at least the voltage "across" the DUT, also maybe the current "thru" the DUT. The point in the discussion I was making that IF a series DC blocking capacitor was utilized to allow DC bias on the DUT, the blocking capacitor could influence the readings and reduce the measurement voltage across the DUT, and if the DUT was a large capacitor WRT to the blocking cap this reduction could be significant and influence the measurement.

Incidentally, the Digibridge 1657 instrument that 2N3055 has, they placed a DC block in the + sense side and because the impedance on the sense side is very high and independent of the measurement, the measurement isn't affected. One the - side a virtual ground by means of a ranged switched transimpedance amp is utilized. The excitation is a voltage source of 0.25VRMS (if I read correctly) and supplied to the DUT thru a switchable range resistor !! This still creates a simple voltage source with a range resistor, and the voltage source must be able to support a DC Bias current that is ~ DC Bias Voltage/Range Resistor. The DUT voltage and current from the virtual ground are measured to compute the DUT value, no AC current source is involved!!

Using a DC block cap on the force and sense (or both together) alleviates the DC Bias problems mentioned, but places restrictions on the DC block capacitor, DUT and potential measurement error associated with such.

Anyway, and interesting situation and likely why LCR meters with a large DC Bias range are more expensive.

Best

Edit: Didn't see 2N3055 post above!

[nctnico]

Most common LCR meters send an AC current through the DUT. Not a voltage. Subsequently the AC voltage is measured across the DUT. Using the phase and amplitude from the AC current and voltage, the various parameters for the DUT can be calculated. So in the end whatever is in series with the DUT gets cancelled out. You can also connect an external DC blocking capacitor in series and you'll still get good measurements. However, if you are getting near the limits of the LCR meter, you'll need to use good Kelvin leads (shielded) and calibrate them at the settings you are using in order to get accurate readings.

Yes agree about AC current use, BTW you can't "send a voltage thru a device", same as you can't "place a current on a device". The measured parameter is always at least the voltage "across" the DUT, also maybe the current "thru" the DUT. The point in the discussion I was making that IF a series DC blocking capacitor was utilized to allow DC bias on the DUT, the blocking capacitor could influence the readings and reduce the measurement voltage across the DUT, and if the DUT was a large capacitor WRT to the blocking cap this reduction could be significant and influence the measurement.

No, a blocking capacitor doesn't influence the measurement unless the current source can't supply a voltage high enough to supply the current (clipping) but in case of capacitors that is likely not an issue. The same for the voltage across the DUT; the input impedance of the measuring input is likely much higher compared to the added impedance of the blocking capacitor. In general a polyester capacitor of a couple of uf is a good choice. However when an LCR meter supports to apply a bias voltage, there usually are blocking capacitors inside the LCR meter already.

[The Electrician]

Most common LCR meters send an AC current through the DUT. Not a voltage.

If this is so, what is meant by a manufacturer specifying the stimulus applied to the DUT as a voltage?  For example, the DE5000 spec says that the stimulus applied to the DUT is .5 V rms.  The Tonghui TH2822 says that the stimulus applied is .6 V rms.

[Kleinstein]

Higher frequency amplifiers don't like a highly variable load, that can also go to the extremes. This is especially tricky with separate drive and sense.
So one kind of needs some added series resistor at the driving amplifier. In a 2 step process the instrument can measure the amplitude at the excitation/sense input and if needed adjust the amplitude of the drive to match the target.
So the amplitude setting would be a bit like a leveling circuit, not a hard voltage drive with sense for drive feedback or a pure current drive.
The feedback is not for every moment in time, but only an average and only for the amplitude, not the phase.

With too low a load impedance it will not reach the target voltage, but can still work with reduced amplitude, and possible going to a more current drive way with a very low impedance DUT.

[mawyatt]

Most common LCR meters send an AC current through the DUT. Not a voltage. Subsequently the AC voltage is measured across the DUT. Using the phase and amplitude from the AC current and voltage, the various parameters for the DUT can be calculated. So in the end whatever is in series with the DUT gets cancelled out. You can also connect an external DC blocking capacitor in series and you'll still get good measurements. However, if you are getting near the limits of the LCR meter, you'll need to use good Kelvin leads (shielded) and calibrate them at the settings you are using in order to get accurate readings.

Yes agree about AC current use, BTW you can't "send a voltage thru a device", same as you can't "place a current on a device". The measured parameter is always at least the voltage "across" the DUT, also maybe the current "thru" the DUT. The point in the discussion I was making that IF a series DC blocking capacitor was utilized to allow DC bias on the DUT, the blocking capacitor could influence the readings and reduce the measurement voltage across the DUT, and if the DUT was a large capacitor WRT to the blocking cap this reduction could be significant and influence the measurement.

No, a blocking capacitor doesn't influence the measurement unless the current source can't supply a voltage high enough to supply the current (clipping) but in case of capacitors that is likely not an issue. The same for the voltage across the DUT; the input impedance of the measuring input is likely much higher compared to the added impedance of the blocking capacitor. In general a polyester capacitor of a couple of uf is a good choice. However when an LCR meter supports to apply a bias voltage, there usually are blocking capacitors inside the LCR meter already.

The blocking capacitor influences the voltage across the DUT and if a current source is utilized for AC test source then this places an additional burden on the compliant voltage for the current source as it must support the voltage drop across the DUT and the DC Block.

[mawyatt]

Most common LCR meters send an AC current through the DUT. Not a voltage.

If this is so, what is meant by a manufacturer specifying the stimulus applied to the DUT as a voltage?  For example, the DE5000 spec says that the stimulus applied to the DUT is .5 V rms.  The Tonghui TH2822 says that the stimulus applied is .6 V rms.

Just checked the Tonghui TH2830 LCR meter we have and evidently this instrument does not utilize an AC current source since you can specify the AC test source voltage, not current, and the AC test voltage source impedance. So we now have the DE5000, TH2822, Digibridge 1657 and the TH2830 all using a voltage source for the AC test source, not a current source?

Maybe someone can show an LCR meter that uses a AC current source for the test source??

Best,

[nctnico]

Most common LCR meters send an AC current through the DUT. Not a voltage. Subsequently the AC voltage is measured across the DUT. Using the phase and amplitude from the AC current and voltage, the various parameters for the DUT can be calculated. So in the end whatever is in series with the DUT gets cancelled out. You can also connect an external DC blocking capacitor in series and you'll still get good measurements. However, if you are getting near the limits of the LCR meter, you'll need to use good Kelvin leads (shielded) and calibrate them at the settings you are using in order to get accurate readings.

Yes agree about AC current use, BTW you can't "send a voltage thru a device", same as you can't "place a current on a device". The measured parameter is always at least the voltage "across" the DUT, also maybe the current "thru" the DUT. The point in the discussion I was making that IF a series DC blocking capacitor was utilized to allow DC bias on the DUT, the blocking capacitor could influence the readings and reduce the measurement voltage across the DUT, and if the DUT was a large capacitor WRT to the blocking cap this reduction could be significant and influence the measurement.

No, a blocking capacitor doesn't influence the measurement unless the current source can't supply a voltage high enough to supply the current (clipping) but in case of capacitors that is likely not an issue. The same for the voltage across the DUT; the input impedance of the measuring input is likely much higher compared to the added impedance of the blocking capacitor. In general a polyester capacitor of a couple of uf is a good choice. However when an LCR meter supports to apply a bias voltage, there usually are blocking capacitors inside the LCR meter already.

The blocking capacitor influences the voltage across the DUT and if a current source is utilized for AC test source then this places an additional burden on the compliant voltage for the current source as it must support the voltage drop across the DUT and the DC Block.

No. As I wrote that only happens if the current source doesn't have enough swing to put enough voltage across the DUT + DC block. However a capactor of several uF will have a low enough impedance for all test frequencies to prevent a limited voltage swing becoming a problem.

Most common LCR meters send an AC current through the DUT. Not a voltage.

If this is so, what is meant by a manufacturer specifying the stimulus applied to the DUT as a voltage?  For example, the DE5000 spec says that the stimulus applied to the DUT is .5 V rms.  The Tonghui TH2822 says that the stimulus applied is .6 V rms.

In the end it is the current through the DUT that matters. But you don't want to apply a large voltage to a DUT so it is limited to avoid damage. Think about what happens when you apply .5Vrms to a 100uf capacitor at 100kHz. The capacitor has an impedance of 16 milli Ohm at 100kHz. With a 'stiff' 0.5V source, the current would be well over 30 Ampere.

[The Electrician]

The stimulus applied to the DUT is provided by neither a voltage source nor a current source.  I see that an explanation of how LCR meters work is in order.

Since we want to apply an AC voltage to the DUT one might ask where will we get this voltage? A basic part of an LCR meter is a signal generator. This signal generator must supply a very clean sine wave of selectable frequency, and in some meters, selectable (or at least, known) open circuit amplitude. Since the voltage applied to the DUT is generally quite low, 1 volt or less, the signal generator is a low power function. This generator is designed to have a 100 ohm output impedance. This means that when a DUT is connected to the test point of the meter it will result in a circuit that consists of an ideal sine wave generator in series with a 100 ohm resistance and then the DUT. The ideal generator will be generating an open circuit voltage selected by the user, or fixed by the design such as .5 volts in the DE-5000. The 100 ohm output impedance of the signal generator and the DUT form a voltage divider so that the AC voltage actually applied to the DUT will be less than the open circuit (nominal) voltage from the ideal generator.

(Some meters have the ability to provide a lower than 100 ohm output impedance for the stimulus generator)

So, the value of stimulus mentioned in LCR meter specs is not the voltage actually applied to the DUT.  It is the voltage generated by the ideal voltage source of the Thevenin equivalent of the signal generator, preceding the output resistance of the Thevenin equivalent.

The meter must then have a phase sensitive voltmeter/ammeter which will measure the voltage actually applied to the DUT, and the current magnitude and phase through the DUT.  The various displayed values are derived from those measurements.

This leads to a problem right away. Consider that the DUT may be an electrolytic capacitor of a high value, hundreds or thousands of microfarads. Such a capacitor will have a very low value of reactance at the typical frequencies where measurements are made. This low reactance loads down the voltage divider (the 100 ohm output impedance in series with the DUT) and means that the voltage across the DUT is small. This voltage may be so small that it's hard to get a good measurement of it. It will be necessary to amplify it with a gain stage, and the noise associated with that gain stage will be the limiting factor determining the accuracy of the measurement.

[Martin72]

Sorry for disturbing here, but I would like to continue in "my" thread...
Seeing the last discussions here, I´ll tear off the meter first before doing anything else.
Will be done "tomorrow", today in the evening, I´ve open it up - Only 2 screws, nice...
Pics will follow, one thing first:
It seems it is the same as the 4401, only a question of software what the testfrequencies concerns.
First look, it doesn´t got any special things, no "chipset" like the DE5000 for example got.
A st32 controller and memory is what I´ve saw on the pcb and "lots" of op-amps.
So this weekend the way is clear, taking detailed pics of the pcb, measure the testsignal via scope for frequency, level and what the bias thing takes an effect.

Martin

[Martin72]

Some compressed pics, on demand I can post one by one separately for better zooming in.

[mawyatt]

Interesting to know if this employs the synchronous demodulation approach and what ADC is utilized.

Doesn't the DE5000 use a Time Domain approach with it's "chipset"? Now need to look at what this DE5000 chipset is and try and figure out how it works!!

Best,

[croma641]

Hi, Martin72,

can You post a measure for  an 1 Ohm (or similar) resistor ?

This is for comparison between this LCR and mine: 4250 Wayne Kerr.

thanks in advance

[Martin72]

Hi croma641,

I can...

Got an Isabellenhuette 1R00, 0.5% Resistor here, on a heatsink.
Measures taken from the ET4410 in DC-Mode and "normal", comparing to a hioki milliohm-meter and the DE5000 in DC-Mode and "normal".
(Of course, everyone was calibrated before)
The values are very close. 

@mawyatt: Will identify the several chips on the ET4410 pcb tomorrow.

Martin

[TheDefpom]

If anyone is interested I wrote a device definition file a couple of months back for these units for the TestController software by HKJ.

[Martin72]

Quick measures done..
Meaning of the level in the display of the ET4410 is rms and without "load".
Pics showing 10khz, 100khz and with bias 1.5V.

More to come...

[croma641]

Martin,

if the reading is stable, and considering the price, that's a (very) good LCR meter .
The strange thing is that HIOKI is stuck at milliohm..

[Martin72]

Hi croma,

Hm? It doesn´t..

[croma641]

My question was about Hioki resolution: apparently it doesn't read hundreds and tents of micro-Ohms in that range.

[pizzigri]

Hi Martin,
can the meter be calibrated by the user? Or it has to be sent back to them?

[Martin72]

Hi pizzigri,

It got a CAL function which automatically detect if the output is open or shorted by the testleads and do a open (or short) calibration of the input.
There is no hint in the manual how to calibrate the unit itself, there are two sealed trimpots on the pcb - I guess, there are the only ones to (re-)calibrate the unit, but actually I don´t know how.
But wil find out someday..

@croma461: In the moment I´ve took the pic the display shows "1.000", it fluctuates a bit of +/-0.001