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Registered Member #5323
Joined: Fri Jun 15 2012, 02:14PM
Location:
Posts: 104
I'm using a gas arrestor to shunt to ground occasional overvoltage spikes that occur in my HV project. I want to use an event counter to 'count' the number of times a discharge travels through the gas arrestor, but would prefer a non-contact method of detecting. The idea is to position a HALL effect sensor (very near the gas arrestor). The HALL effect sensor would be connected to an event counter that displays the number of times a discharge has occurred through the gas arrestor over an extended period. Good idea, bad, delusional? I seek the guidance and wisdom of the group before I spend time and money bread boarding the circuit.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
this may be useful for me too. but i wonder if a hall sensor is best. mine arrestors are opaque so that rules out optical means, but i wonder about a triple plate capacitor. for non-contact i believe the choices are 3. E-field, M-field and optically. if im missing a method someone please post it. all but optical have false positive or false negative noise issues.
in high voltage circuits and measurement, as we all know signal to noise is more difficult for us then some EE making a 3.7 V Ipod or wrist watch.
non contact, isolated or "almost" isolated is best. i believe thats what you're getting at and i agree.
keep in mind i loath the thought of programmed digital and microcontroller type semiconductors for the work many of us do here on the forum. but increasingly i find my self looking at Arduino and fiber optics for control, sequencing and special timed events.
* there are polarimeters that use special glass or super poisonous liquid chemistry to alter the light intensity based on voltage. but that may be to sophisticated.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
With Hall (not HALL) effect sensor, you're trying to detect the magnetic field caused by current through the gas discharge tube (GDT) surge arrester. Have you run the numbers? Wouldn't the signal be stronger if you put the sensor close to a lead wire, instead of the same distance from outside of the GDT itself? You could greatly improve the sensitivity by using a ferromagnetic core around the lead wire, with a gap for the Hall sensor. Or make a few turns with the wire that's carrying the current through GDT.
If you want to count discharges that come in short pulses, I think a simpler non-contact solution is a current transformer like those in inductive timing lights. You can get those very inexpensively at yard sales, craigslist, ebay, etc. New ones are still sold at auto parts stores, Harbor Freight, etc.
Or some little pre-wound toroid coil with room in the middle for a wire in the gas discharge tube circuit. They have them inside GFCI electric outlets.
Whether you use Hall sensor or induced voltage: if noise spikes are a problem, consider an electrostatic shield between the sensor-counter circuit and the HV circuit. A current transformer or Hall effect device can sense current in the inner wire of a shielded cable, as if the shield weren't there. Unless a countercurrent is flowing along the shield.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
klugesmith wrote ...
A current transformer or Hall effect device can sense current in the inner wire of a shielded cable, as if the shield weren't there. Unless a countercurrent is flowing along the shield.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
To clarify that comment: if you run a shielded cable through the window of a current transformer, the shield must not be grounded at both ends. That would make the shield a shorted turn, and it would automatically carry a current that nearly cancels the desired primary current.
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HALL effect sensor to detect and count discharges through a gas arrestor?
