Hall effect sensor failure mode
Hall effect sensor failure mode
(OP)
My Fisher Paykel dishdrawer uses a Hall effect sensor to check motor rotation. The service manual says it should have a resistance of 3 to 4 Mohm measured +ve centre, -ve outer, for each of the two outers.
Instead my Chinese Fuke brand (I see what you did there) meter tells me it is about -3 Mohm. That is not enormously helpful, does a typical DVM get confused like that?
Instead my Chinese Fuke brand (I see what you did there) meter tells me it is about -3 Mohm. That is not enormously helpful, does a typical DVM get confused like that?
Cheers
Greg Locock
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RE: Hall effect sensor failure mode
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RE: Hall effect sensor failure mode
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Hall effect sensor failure mode
Yes, when measuring semiconductor devices, the cheap ones can give weird results. Even the good ones will give weird results if you have voltages on the device other than from the meter. As IR says, make sure you isolate the leads and re-test.
RE: Hall effect sensor failure mode
The whole thing is DC, off a switched mode power supply, so even when the mains plug is pulled out the DC side is still somewhat live.
OK, I'll pull the little bugger out and put it on the table. thanks.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Hall effect sensor failure mode
I'm curious about why the absolute value happened to be spot on - coincidence?
RE: Hall effect sensor failure mode
Mike Halloran
Pembroke Pines, FL, USA
RE: Hall effect sensor failure mode
A (-) negative reading when the DVM is set to Ohms indicates that there is a current still in the circuit, spoofing the resistance measurements, as others have said. When taking an interest in semiconductors it's nice to get a DVM that can test them properly. Look for the ones that have a "-|>|-" setting.
A semiconductor like the Allegro HE sensor has even odds of failing to short or to open. Since the semiconductor is just bonded to a continuous shunt, there's low risk of the shunt failing open. However, the cross-section of the shunt is very small compared to the supposed current rating of the sensor assembly. Lots of opportunities for error, especially with the screw terminal variety. I know of some folks who have used them with small wind turbines, but I wouldn't dare to. Allowing the power line circuit of a wind turbine to fail open would invite disaster. Since you're using solar, an open circuit isn't inherently disastrous. Unless certain consequences of the open-circuit are.
STF
RE: Hall effect sensor failure mode
Anyway I have pulled the thing out and in the process of a slightly aggressive inspection, ie prodding it with the probes, the rather corroded sensor fell off the rather corroded circuit board.
So, I've ordered the part, but it is on back order, and also ordered 10 of each hall effect sensor I could find on ebay, for about 10c each.
Frankly I'm not wildly impressed that a PCB in a dishwasher under the pump unit is installed without encapsulation. The rest of the machine is neat, that detail is gross
The chip appears to read W10 4878 but I can't find that using google.
The real mystery is what the Hell are the 4 pads between the chip and the socket? presumably some abandoned wiring from a previous system.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Hall effect sensor failure mode
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Hall effect sensor failure mode
Ah yes, corrosion - I've had the voltage/current generated by (ok, take your pick - thermocouple emf, galvanic (corrosion) cell, cosmic rays) spoof a sensitive circuit into triggering at random moments.
RE: Hall effect sensor failure mode
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Hall effect sensor failure mode
The circuit card was designed to also accommodate an older or alternate type of Hall effect sernsors that might have required external resistors, to be installed on the empty pads. But the newer or other alternate Hall effect sensor used here are fully integrated and the same circuit card is used simply to connect the sensor IC to the wiring connector.
Pure speculation.