Thermocouple High Voltage Isolation

Thread Starter

HighVoltage!

Joined Apr 28, 2014
181
I plan on experimenting with a device that I intend on applying 50kV 60Hz for 30 minutes. During that time frame, I would like to monitor the surface temperatures with TC's. Unfortunately, if the device fails, the casing will go up in voltage, which could damage my temp meter (it is also not safe as well). What can I use to safely and accurately monitor temperatures?
 

Reloadron

Joined Jan 15, 2015
7,543
50 KV is one thing. How much max current can we expect to see? Can we use an ungrounded TC with a grounded sheath? This would go much better with a better description of the object we are measuring what I assume to be surface temperature of. One sensor or a half dozen? Surface material type?

This will not work for me. I need to to be able to access all sides.
This is what I am getting at, please present all the facts up front.

Ron
 

Hymie

Joined Mar 30, 2018
1,284
I very much doubt you will find a commercial product offering this level of voltage isolation for thermocouples; a quick search brings up isolation devices rated to 1500V~ (I suspect for applications where mains may be applied at the junction).

I have experienced electrical noise where the junction is located close to a high voltage source, the trick is to de-energise the test subject and the noise instantly disappears (allowing a valid temperature reading to be taken).

With the above in mind, you could bring the test item up to temperature and only connect the thermocouples to an instrument with the test subject de-energised. Of course there would be a time lag in obtaining temperature readings, during which the temperature would drop. Depending on how many thermocouples you connect, you could measure each in turn (multiple times), starting at time zero (being when the EUT was de-energised) and then make a plot of each thermocouple temperature Vs time and extrapolate back to time zero.

With such a high voltage, I would go nowhere near the thermocouples with the EUT energised (and assume them to be at 50kV).
 

nsaspook

Joined Aug 27, 2009
13,418
You need a floating measurement system were the TC and assorted circuits (battery power is the easiest solution) are at the same potential as the object being measured with opto-isolation for the data link. We have dopant vaporizers that operate and are controlled remotely via fiber links that are hundreds of thousand of volts above the earth ground potential. We use a isolated shaft motor generator for instrumentation and control power on system > 100kV with a high voltage isolation transformer for lower voltages.

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Ion source vaporizer
 
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