How to check instruments ground connection relibility?

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steve_rb
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How to check instruments ground connection relibility?

Post by steve_rb » Tue Nov 11, 2014 10:08 am

We have a few expensive instruments in our lab. I would like to check their ground connection and condition of the ground well and ground rod to be sure there is no risk of damage to the instruments due to high ground connection resistivity. But I have no experience in this. After reading a lots of documents I realized there are 4 prob and 3 prob ground resistivity measurment methods but non could help. Anyone has experience with how to measure each instrument ground connection resisitivity?
Is that possible to measure this resistivity using a normal ohm-meter? If yes how?

John Futter
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Re: How to check instruments ground connection relibility?

Post by John Futter » Tue Nov 11, 2014 5:29 pm

Steve
No you can not use a multimeter.
There are special earth bond testers that use a pulse to measure the earth impedance. Note I said impedance and not resistance.
As an electrically registered person I have to use this equipment to make sure that any faults do not allow for an unsafe situation

steve_rb
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Re: How to check instruments ground connection relibility?

Post by steve_rb » Tue Nov 11, 2014 7:57 pm

Could you please let me know what equipment is suitable for this purpose (brand, model, ...) and which one you are using?
Also if you can briefly explain about the measuring method that will be very helpful.

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Chris Bradley
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Re: How to check instruments ground connection relibility?

Post by Chris Bradley » Tue Nov 11, 2014 9:43 pm

John, I have always thought that if I were to want to set up some earthed points, I would sink two earth points then try to apply a high current low voltage between the two. I would then know the resistance between the two points via earth, so if I then link them in parallel I'd have a connection to earth that was a quarter of that which I measured by the voltage drop between the points with the current power supply.

Would this be an appropriate 'DIY' way of doing it, if I were to want to install such, or are there unforeseen snags I am not anticipating?

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Bob Reite
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Re: How to check instruments ground connection relibility?

Post by Bob Reite » Wed Nov 12, 2014 1:29 am

You can use the "fall of potential" method which involves the ground under test, two temporary reference ground rods, an isolated signal generator and a voltmeter. Rather than go into a detailed description here, I'll give a link to a web site with a good description of the technique.

http://www.esgroundingsolutions.com/abo ... e-test.php
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.

steve_rb
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Re: How to check instruments ground connection relibility?

Post by steve_rb » Wed Nov 12, 2014 2:41 am

I more want to test the ground connection impedance from where the instrument is connected onward. if you have a good low impedance earth rod inside the well but earth cable goes from the instrument to the rod inside the well is not good that means you wound get any benefit from that rod and well. I want to check if any connection is bad in the middle from the instrument to well as well as the well impedance. Also I have heard ground impedance measuring instruments have calibration which if it is not correct this could cause high ground impedance. right?

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