Measuring low current (nano Amps) but at high voltage (300-500VDC).

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The project is to measure the resistivity of a sample which is a high value so I have to pass High Voltage through the sample in order to get a large enough current to measure and the use ohms law to calculate the resistance.

I have tried hall effect sensors and there was not enough signal to measure.

My thought is if I isolate my grounds and use either the usb-isolator or bluetooth I might be able to use the CurrentRanger.  I understand the danger of connecting the HV DC ground to the CR.
I have used the usb-isolators in similar situations, but I'd like advice if this is doable or foolish to attempt with the CR. I will need to make thousands of measurements so I need a robust solution.

I welcome any comments or suggestion on my project.

[Felix]

Hmmmm. Nanoamps but high DC potential. I have not tried it but I don't think it should be a problem.
The reason being that the CR is a differential high side current meter. So whether you are at at few volts above ground or 500v, it does not care, as long as it is floating WRT earth ground.

Now when you start connecting other things to it which might cause a loop to ground somehow, you can damage it. A floating DMM that just reads the raw output is fine, that is also isolated from everything else and is also a differential multimeter, it just samples the DC/AC potential difference between 2 points, simple, doesn't care what those 2 points are (a battery or your wall AC outlet).

Over time I made the CR a bit more robust to bad user behavior but there is no galvanic isolation, like you may have on much more expensive meters. And you don't really need it, if you know what you are doing and understand a few simple principles, you will have a long happy life with the CR.

If you want to log via USB or do something with the GPIO you have to start worrying a bit more because although many isolators make different claims, the higher that isolation the more serious the problem becomes.

At the end of the day I cannot warmly recommend doing this without extreme caution, or offer guarantees or warranties. It was primarily designed and intended for low power DC measurements but it may be used in other scenarios, and I've seen in done in all kinds of automated test fixtures and what not. Given that the current is so low, that is a little better than straight 500V at a few mA or more. So just be careful, use robust isolation if you want logging, or just use the bluetooth if slower sampling is good enough.

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I'm aware of the dangers and have experience in taking differential measurements and isolation of grounds.  I have several potential applications for the CR.
I plan on originally using the CR with the SSD1306 0.96" I2C OLED Display and a battery.  I want to see the repeatability of the measurements.
Later I will use the bluetooth as I need to put these measurements into a database for report generation.
Do you know how long it would take for two CR to be delivered to New Hampshire USA?
Looking forward to using these in various projects as we do a lot of low current measurements for our customers.
Thanks for your prompt response to my previous post.

[Felix]

Do you know how long it would take for two CR to be delivered to New Hampshire USA?

Depends on what delivery service you pick. A few days my guess, regardless. If you want fast pick PRIORITY or EXPRESS.

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The Battery I ordered had the pins reversed on the plug. Thankfully I did not damage the CR but I did discharge the Battery.  I have since charged the Battery and had success using the CR.
Interestingly I was able to measure the current with as low as 10 VDC applied. I started at 100VDC and then 200 VDC and finallly 300 VDC and the readings were right on for all three voltages.
I thought I would try a lower voltage and was surprized when the CR read 1/10 of the 100 VDC current at 10 VDC.  I might be able to use a safer lower voltage.
Will have to consult with the Engineer In Charge to see if there is a requirement to use the HV vs 10 VDC. The objective was to calculate the resistance of a sample by measuring current.
I think they were using the HV because they were unable to read low currents and the current would be a higher value for using same resistance at a higher voltage.
I will let everyone know how it turns out.  Looks like the CR is exactly what I needed for this application.