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Solved? - Hall effect probe for superconducting magnets
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ChristofferB:
Hi all!
I've been given a gaussmeter from my uni, a 70's vintage Systron Donner 3101.
A probe came along with it, but the probe is clearly from a different instrument, since it has a vastly different connector.
I'd like to try and get the probe tested before messing with the huge rack instrument.
Here is what is known:
- It's a flat ceramic chip hall effect device on the end of a probe, model and manufacturer has been too smudged to read. Probe is potted.
- The connector reveals 3 pairs of leads and a shield. I believe the pairs to be coaxial with individual shield:
Connector pin wire colors:
- White + Black
- Red + Black
- Green + Black
- Cable shield
-None of the black wires are connected to each other or to main cable shield.
A hall effect device needs a current between two ports, and a voltage differential is extracted via two others:
Since a pin is lacking for that, it stands to reason the current supply might be using its shield (black wire?) as return,
and the two remaining colored wires are V+ and V-
How will I go about testing this? What voltages/currents are usually used with naked Hall effect devices? Keep in mind, I believe modern Hall effect devices already has a regulator and current reference built in.
Thanks in advance!
ChristofferB:
Ok so I've stripped the probe element, and it seems 6 wires lead to it. There is a small black nodule at the silicone strain relief right by the sensor which could be a thermistor, as a hall device really only should need 4 wires. I'm considering breaking these out to some headers for easier access, but it still doesnt solve the issue of pinout...
Is there any semiconductor junctions in a hall device that can be checked with a diode checker?
ChristofferB:
2 of the leads are almost certainly an NTC - at room temp. They have a resistance between them of 1.8K, when freezed with a freeze spray it shoots up over 10K. (white+black pair)
Makes sense for a probe for a cryogenic magnet! That leaves only the 4 wires that would be expected!
ChristofferB:
Okay, almost got it figured out!
Applying +5V through an 1K resistor to the green+black pair gives a voltage between 0 and 1 mV out on the red/black pair when a powerful neodymium magnet is brought near.
I still have no idea what voltages/currents is expected for a device like this, although I think sensitivity is set with the bias current.
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