LCR measurement, DC Bias up to kV level - Page 1
Forum section: electronics / projects

author: Aheld
author_rank: Regular Contributor
timestamp: October 25, 2023, 07:32:27 pm
content: Hello,I‘m searching for a solution to measure capacitance values with bench LCR meter up to DC bias voltages of approx 1600V.I know the solution for Keysight B1505 LCR option (very expensive) but I‘m wondering if there are other solutions available?What about self made solution? Any suggestions or ideas?Br. Aheld

author: coromonadalix
author_rank: Super Contributor
timestamp: October 25, 2023, 07:45:30 pm
content: or the sencore lc 102 and lc103 up to 1kvwho's expensive as hell

author: jbb
author_rank: Super Contributor
timestamp: October 25, 2023, 09:04:45 pm
content: You can make a DC V offset box by capacitor coupling the force and sense lines of the LCR meter… there’s an old HP app note about it somewhere.But 1600 V is pretty high. Once you go near or above 1 kV, you start needing to really worry about insulator breakdown, arcing, creeping etc. That’s one reason for the sharp drop-off in available test gear (other being sales volume I think).Do you need to do a lot of measurements? If it’s only a few, it may be easier to get in touch with local commercial test laboratories.What frequency range do you need to test over? If you need to go down to low frequencies, AC coupling caps get huge. At higher frequencies, parasitics in your test jigs could become a problem.Example calculation:Test freq: 50 HzLCR meter internal Source impedance R: 50 OhmsSuggested capacitor impedance: 50/5= 10 Ohms or lessSuggested Source capacitor value: 318 uF or higher(Sense capacitor can apparently be quite a bit smaller.)Stored energy at 1.6 kV: 407 Joules. Yikes.

author: mawyatt
author_rank: Super Contributor
timestamp: October 26, 2023, 12:24:20 am
content: Here's something that might be of interest.https://www.eevblog.com/forum/projects/bias-network-for-lcr-meter/Best,

author: Terry Bites
author_rank: Super Contributor
timestamp: October 26, 2023, 10:29:10 am
content: AN346?

author: Kleinstein
author_rank: Super Contributor
timestamp: October 26, 2023, 11:16:17 am
content: For a capacitor to test, one could use 2 in series and add the bias in the middle. This would test the sum / average of both parts.

author: Aheld
author_rank: Regular Contributor
timestamp: October 28, 2023, 05:30:45 pm
content: Hi,Thank you very much for your replies and comments.It seems to be not so easy to measure above the typical 42V. I know the HP app note for the 200V adapter.@mawyatt: this I didn‘t know, very interesting@jbb: my plan is to measure a lot of devices at 1MHz in a kind of automatic setup.@coromonadalix: I don‘t know this manufacturer. Is the equipment reliable?Br aheld

author: Slh
author_rank: Regular Contributor
timestamp: October 28, 2023, 06:08:54 pm
content: Perhaps a dumb question, but do you have the bias source? 1600V is an unusual DC voltage and outside the usual LV (1500Vdc, 1000Vac) range. If I were doing it then I'd probably grab our hipot tester and have very slow ramp times. It might be difficult to properly calibrate the test rig with the hipot tester though.I've measured inductor bias with a Nanovna, DC blocking caps and an AC blocking inductor on the power supply. You should be able to do the same for capacitors (with care). It might be tricky to get good numbers at 1MHz but maybe relative measurement will be ok?

author: mawyatt
author_rank: Super Contributor
timestamp: October 28, 2023, 06:58:25 pm
content: At 1MHz the DC isolation capacitor can be a small value, however this must be a very good quality dielectric such a COG, that have a very low voltage coefficient. Some of the film type capacitors might have good enough voltage coefficients, also check for operation at 1MHz..You can utilize the LCR method we described above or an VNA, be very careful to protect your test instrument.In the case of our LCR method, would strongly recommend using a safety feature where the DUT is isolated from the DC source & test instrument initially and connected via relay to shunt discharge resistor to dissipate any HV on DUT. Then the DUT is connected to test Instrument, then and only then is the DC source connected to the DUT thru a high value and high voltage resistor (maybe a series RFC inductor also). This should slowly charge up the DUT to the required voltage which can be monitored with a high value and voltage sense resistor like shown in our setup. Once the measurement is complete the DUT should be electrically removed from the test instrument and connected to the discharge resistor. This type procedure can be facilitated with relays, timers and push to test buttons.The test instrument should be protected with protection diodes as we've shown, maybe even doubled up protection just for test instrument safety.BTW are you testing SMDs? If so, the SMD fixture shown in #14 of our link above could be configured for the HV DC bias measurements since the DC isolation capacitors will be physically and electrically small for 1MHz use.Anyway, just some thoughts on how to achieve your goals, and still have your test equipment survive!!Good luck and keep us posted on your progress.Best,

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: October 28, 2023, 10:04:37 pm
content: One reason I like the old General Radio Corp. bridges is they can handle high bias voltages, 600 or more volts, but this is way beyond that! Keep us posted.