121GW Voltage Readings WAY WAY Off. Not a 121GW general issue

[daveyk]

121GW Voltage Readings WAY WAY Off.   Not a 121GW general issue. Moderator, if you think it is move this message please.

I was trying to trouble-shoot with my 121GW.  It hadn't used in several months.  I was checking out a few on-board power supplies of an instrument I am trying to check.  The 6 volt supply was reading 8.444.  I trouble-shot that for an hour then I used my Agilent DVM and it read 6.001 volts!  Son of a bxxch!!!

I've never used the 121GW for voltage measurements, just ohms and didn't like it very much for that and really just set it aside after that.  Now this.  I am using the exact same set of meter leads by the way, I just moved them between DVMs.

I think it may be time to give this 121GW a toss.  It never has been right since I bought it and now, I suspect it is over a year old now.

Dave

[NoisyBoy]

With reading this far off, the first thing I would check is to put in a fresh set of batteries.

[ggchab]

The position of the rotary switch is not always perfectly correct. I had the problem with the resistors'range a few times and it gave incorrect readings.

[rsjsouza]

Does teh voltage have AC components as well? If so, check:
https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/msg3015706/?topicseen#msg3015706

Otherwise, let me know if you plan to toss it... I may be interested.

[dcac]

Also check if the error persists if you change range.

[dcac]

oh and after having a very similar incident - for troubleshooting I now only use a DMM I know and can trust, and so far my 121gw doesn’t really qualify, though that being said when measuring DC voltages it’s been within spec. so far - at least as long as it’s been a clean DC voltage.

[joeqsmith]

121GW Voltage Readings WAY WAY Off.   Not a 121GW general issue
....
Dave

When I first started to test the two meters I bought, one made some bad measurements right out of the box.  I always assumed it was the switch as after a few cycles it cleared up.   

[daveyk]

"Does teh voltage have AC components as well?"

I've tested it right on my E3632A power supply in parallel with my 34401A.

No idea what is going on.  It the batts are low, the indicator is not on.  It was fine about two months ago.  Now that I finally went to use it (instead of my Fluke handheld), it does this.

[daveyk]

"With reading this far off, the first thing I would check is to put in a fresh set of batteries."

Bingo!  It had four really nice Duracell AA batteries in it and did NOT get used much at all.  In fact, it has probably sat two months without being touched.

I wonder if this meter draw current went not turned on?

All I had was some really crappy Harbor Freight batteries to put in it.  I have to dawn the mask and head to Wallyworld today; I'll pick up some AA batts there, perhaps some Lithium AA.

Funny thing is, I did not notice a low battery indicator.  I really didn't notice anything wrong with the meter at all until I figured out it read worse than a dead dingo's willy-rod (or some weird term like that - lol).

Dave

[daveyk]

Thanks Joe.  It was bad batteries, although no low batt indicator for some reason.  I've seen portable instruments were the battery voltage was high enough to keep battery indicators from working, but could not supply current to properly operate the device.  That may have been the case here.

[daveyk]

It's working "Okay" again.  I guess that's close enough for trouble-shooting purposed.  It's how it always has compared to two certified 34401A metes.  I assume .003v low is good enough.  Now it the Auto-Ohm was just faster. v2.02 firmware.   It's acceptable now.

This thing just threw me for a loop yesterday and cost me about an hour and confused the heck out me. You have to rely on your test equipment.  As cool as this meter is, I most often grab very, very old Fluke 75 or very, very old Fluke 83 (just recently fixed the display). I trust those meters more than the 121GW.  I still waiting for when I need that 15v diode check, which would set this meter apart.

Dave

[NoisyBoy]

Good to hear it is back to normal.  I don't trust the low battery symbol on DMMs, and changing battery is an easy test, that's why I always suggest people to try that first before opening up the meter.

No matter how good a DMM is, I prefer to have more than one, ideally 3+.  That way, when one reading is off, I can tell which one is truly off. 

[daveyk]

"Good to hear it is back to normal.  I don't trust the low battery symbol on DMMs"

There can be a science to battery level detection and it is not always the voltage (99% of the time it can be - lol), sometime rare times it can be a current delivery issue.

The 121GW us smaller and prettier than either of my mid-1980's Fluke 75 or Fluke 87.  Resistance AUTO mode still tests me at times.  It works well in manual range mode, but rolling through the manual mode selections still confuses me. I don't feel what mode/range you are in is well enumerated on the LCD.  I do not think it's a dot matrix LCD display, so we have what we have and enumeration can not be fixed in firmware.  Dave could have made better choices in the LCD display mode indicators during the design process.  It is what it is, I need to learn it better (although I shouldn't have to learn a DVM).

When you trying to repair an instrument, it is okay that the broken instrument confuses you, it's not okay for your test instrument to confuse you.

Again; thank you an take care.

[rsjsouza]

@daveyk, thanks for reporting back the outcome of your predicament. I haven't had issues with battery indicators yet, but recently I suspect that several of my banana probes are starting to bite the dust - that or the meters' jacks. When making a measurement, I have to frequently rotate the plugs or wiggle the cables to get a solid "near 0Ω" reading.

That drives me nuts when I make a reading and the measurement fluctuates...

[joeqsmith]

Thanks Joe.  It was bad batteries, although no low batt indicator for some reason.  I've seen portable instruments were the battery voltage was high enough to keep battery indicators from working, but could not supply current to properly operate the device.  That may have been the case here.

Odd.  I tried the production unit that was not stressed using a 10V reference.

Vbattery,  121GW Readout,  Low Battery Indicator
4.895, 9.999, Off
4.557, 9.999, Off
4.218, 9.999, On   (this is close to the threshold)
3.978, 9.999, On
3.768, 10.000, On (this is where the meter will start to go inaccurate)
3.301, 11.062, On
2.596, 15.723, On
1.963, 30.24, On  (this is pretty much where the meter will cut out)

[TrickyT]

So glad this thread exists! I just had the same problem: voltage readings way off but low battery indicator normal. Problem was low batteries. Replaced those and all is fine again. This forum is such a good source of information! 

[BeBuLamar]

With reading this far off, the first thing I would check is to put in a fresh set of batteries.

I think the 121GW is a decent meter and any meter that can be considered decent can't have wrong reading when the battery goes low. It should display a low battery sign first then quit working altogether but not giving wrong reading. If it were to give wrong reading when the battery is low then you always have a chance ot have bad reading.
Since the OP said it's the battery problem then I would never consider this meter. It's simply junk.

[Kleinstein]

A not working low battery detection is a defect that may go unnoticed for quite some time. Not sure if it is actually tested in production.

Normally it should not make a real difference, but there are different ways batteries go bad:  Dry cells and many LI primary cells pretty much keep the no load voltage, but the internal resistance goes up. Alkaline cells stay relatively low resistance, but gradually get a lower voltage even at low load.
There is a slight chance the low bat detection may fail with dry cells.

[TomKatt]

If the meter can become that inaccurate resulting from low battery voltage - that doesn't trigger the low battery warning - I'd have a problem relying on that meter going forward...   Because you'd basically have to verify some test measurements every time you used it.

Like the OP, I've chased rabbit holes based on bad test result before.  And once you've been burned like that, you tend to be gun shy going forward - especially if you're using the same test gear.

Something seems like a poor design issue going on here.  If low battery voltage causes measurement errors to that degree, it should most certainly light the warning light.

[BeBuLamar]

If the meter can become that inaccurate resulting from low battery voltage - that doesn't trigger the low battery warning - I'd have a problem relying on that meter going forward...   Because you'd basically have to verify some test measurements every time you used it.

Like the OP, I've chased rabbit holes based on bad test result before.  And once you've been burned like that, you tend to be gun shy going forward - especially if you're using the same test gear.

Something seems like a poor design issue going on here.  If low battery voltage causes measurement errors to that degree, it should most certainly light the warning light.

In fact it should turn itself off before giving inaccurate readings.

[BILLPOD]

Pressing the yellow 'Setup' button several times will give you several different results displayed in the upper-right corner of the display.  One of the results is the voltage of the batteries in the meter.

[TomKatt]

Pressing the yellow 'Setup' button several times will give you several different results displayed in the upper-right corner of the display.  One of the results is the voltage of the batteries in the meter.

Beyond putting the liability on the user rather than the device, at what battery voltage do you deem the readings produced by the meter inaccurate?

The ability to view battery voltage is not an acceptable solution to me.

[AVGresponding]

A not working low battery detection is a defect that may go unnoticed for quite some time. Not sure if it is actually tested in production.

Normally it should not make a real difference, but there are different ways batteries go bad:  Dry cells and many LI primary cells pretty much keep the no load voltage, but the internal resistance goes up. Alkaline cells stay relatively low resistance, but gradually get a lower voltage even at low load.
There is a slight chance the low bat detection may fail with dry cells.

The only way I can see this happening is if the battery monitoring either isn't real time, or is just not fit for purpose; if the no-load voltage is good, when you switch the device on the internal cell resistance will cause the terminal voltage to fall (in proportion to the current draw, obviously), and I can't understand how it could be simultaneously high enough to fool the low battery warning, and low enough to cause malfunction, unless the battery monitor is very badly implemented.

[Kleinstein]

I am also not convinced that a wrong battery type is causing the problem. There is at least the possibility, if the current consumption is not constant, but higher during part of the conversion, compared to the battery check. It case this is an hardware issue (e.g. the battery testing part failing at really low battery) it may be worth testing the reaction to low battery voltage with a few different meters. It looks like most meters work OK.