EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: tbj on March 14, 2013, 03:20:34 pm
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Hi,
My main meter - not particularly expensive, but less than a year old and I'd rather not have to replace it right now - has gone odd recently.
(http://i.imgur.com/1okqSOkl.jpg)
Here it is reading a negative inductance value with the leads shorted.
Also doesn't seem to read stably on ohms or volts - value keeps fluctuating!
Anyone have any idea what could be up with it or if there is any sort of reset procedure for these?
Cheers.
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Start by using the right connections. :palm:
The most right two busses
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Mmmm....I don't think so Pa4tim.
I would have a look at the PCB, to make sure everything appears normal.
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Replace the battery.
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Ok, i could not read the text on the meter, only that it was umA and the com was not used. And I do not know the meter. This is the first time I see inductance on a multimeter.
I think it is a simpe I/V converter. It could be it uses a AC signal to measure the current through a shunt ( or better the voltage drop over that.) if the battery is low a good meter still makes correct measurements. To bad some meters change there measuring results as a function of the battery voltage. If is not a "good" meter ( based on the huge Chinese toys fanbase here >:D I leave this in the middle) i would guess the battery too.
If not, there is something wrong, is it still within the exparation term ehh, warranty term ;)
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It's time to read the manual. :)
To measure inductance you have to set the meter to inductance, connect the DUT and then press the LC button. Without the last step my meter also shows negative value, but I just verified it on known inductors I have and it's as accurate as it can be. Just as a note for the interested, it's supprisingly accurate on inductance ranges for a device of its class.
As for the readings, what's the order of those fluctuations? Maybe it has something to do with probes supplied with the meter, like tip oxidation? Checking the battery also wouldn't hurt.
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Thanks guys - I RTFM'd and also changed the battery. All working now.
Boy, is my face red now. :palm:
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Mark noted some problems with the lack of low battery indicator UT-70D in these two videos. Yes, I realize you have an "A", but maybe the "A" and "D" have the same problem?
UNI-T Model UT-70D Multimeter Review (https://www.youtube.com/watch?v=GkBi9a4C6kU#)
UNI-T Model UT-70D Low Battery Indicator Problem (https://www.youtube.com/watch?v=eYoadGf6sI8#)
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My UT70A is also weird.
UT70A odd behaviour on hfe range (https://www.youtube.com/watch?v=lBJJrkUiD7Q#)
When you are in the hfe range and you short the two middle sockets, the LCD goes blank. It looks like the 9V battery was overloaded at that moment. I think that it is not a fault but a poor design...
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On my ipad the schematic is hard to read so I must be wrong. I probably overlook a Voltage regulator or Reference because it looks like the Vref is made by a voltage devider made by R82 and R83 between the battery and ground.
Is this really true ? I have only seen that used for ultra cheap multimeters before ( the 5 -10 dollar supermarket meters)
In that case the measurement results depend very much on the battery voltage. That is in my opinion the biggest no-no in multimeter design.
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On my ipad the schematic is hard to read so I must be wrong. I probably overlook a Voltage regulator or Reference because it looks like the Vref is made by a voltage devider made by R82 and R83 between the battery and ground.
Is this really true ? ...
The schematic is definitely hard to read. Looks a bit like a 7106, in which case it maintains the COM pin (ground) at 2.8V below V+ with an on-board regulator.
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Otherwise I am quite satisfied with this multimeter...