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I have a new digital multimeter (Kopp GCM-620) that has auto ranging, and an overload indicator on its LCD.

When testing a mains outlet (the voltage where I live is 230V), the LCD shows a reading around 220V-230V, but the overload indicator always comes on as well.

I'm a bit concerned about the fact that the overload indicator is showing up every time. The multimeter is rated up to 600V AC. Is there any good reason for the overload indicator to be appearing when the voltage readout is far below the voltage range that the multimeter is capable of? Is it possible that the multimeter itself is faulty? Or is this normal on an auto ranging, digital multimeter?

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  • \$\begingroup\$ Nothing to do with electronic design. Question should be closed. \$\endgroup\$ – Leon Heller Jan 30 '12 at 21:49
  • \$\begingroup\$ @mtnorthrop Does the indicator come one when you first connect the meter or does it come on even after it shows the voltage? \$\endgroup\$ – AndrejaKo Jan 30 '12 at 22:18
  • \$\begingroup\$ It comes on when I connect the meter to the outlet, and stays on until I take the leads out of the outlet. \$\endgroup\$ – mtnorthrop Jan 30 '12 at 23:10
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    \$\begingroup\$ @LeonHeller: The site description at stackexchange.com is "Q&A for electronic hardware hacking enthusiasts". This question would seem to fit that description. If the site is supposed to have narrower scope, perhaps that description should be updated to reflect that? \$\endgroup\$ – supercat Jan 30 '12 at 23:23
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The behavior you are seeing is pretty typical. When there isn't any voltage connected, a typical meter would set itself for the 0-299.9mV range (it has no idea whether you'd be interested in e.g. a 0.4mV signal, but the only way it could display such is at the 0-299.9mV range). When you connect 230V, the meter will start by trying to display 230V on the 0-299.9mV range. It will be too big, so the meter will show "overload" and its next reading will try to display 230V on the 0-2.999V range. That won't work either, so the meter will show "Overload" and switch to the 0-29.99V range. Again, "Overload", but then it will switch to the 0-299.9V range. That reading will be within bounds, so the meter will display it.

Some meters are designed so that they can switch between ranges very quickly, so as to minimize the time that an "overload" indicator is shown. On the other hand, momentarily displaying an "OL" indicator may help draw a user's attention to the fact that the decimal point is moving.

In any case, with many meters, if you wish to avoid the annoyance of having the meter change ranges, you may be able to manually select the range the meter is supposed to use. This may be very handy when trying to observe intermittent voltages or currents. Having the meter start out on the 0-299.9mV range when a 240V input is connected won't damage the meter, but will increase the time required before it starts showing a valid reading. Selecting the 0-299.9V range in advance will make it possible to measure pulses which would be too short to measure using the auto-ranging function.

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  • \$\begingroup\$ Thanks for your answer. Based on this, it sounds like the multimeter that I have is functioning normally. The overload symbol stays on the display for the whole time I have the meter connected to the outlet, even though the reading shows an accurate ~220V almost immediately. It is possible that, with the model I'm using, once the overload symbol appears it stays on the display until the voltage drops to around 0. \$\endgroup\$ – mtnorthrop Jan 30 '12 at 23:13
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    \$\begingroup\$ @mtnorthrop Can you test the multimeter with another voltage source and see if the overload sign stays? After reading the manual, I found this part Overload Indication - This is the display when the input exceeds the display capability of the Meter. If measuring voltage or current, remove the input immediately.. Furthermore, the overload indicator used there is not the standard OL indicator which is usually displayed by multimeters when they switch from lower range to upper. To me this looks like a defective unit. \$\endgroup\$ – AndrejaKo Jan 30 '12 at 23:51
  • \$\begingroup\$ @AndrejaKo When testing voltage on batteries, for example, the overload indicator (a special symbol on the LCD for this model) does not come on. Only when testing a mains outlet. Your quote from the manual is exactly what I read as well, and I was wondering what the point of an overload indicator is if it comes on and stays on when during normal use. Is there any chance this could happen due to a weak battery? I'm using the battery that was packaged with the meter, and I haven't confirmed if it's good. \$\endgroup\$ – mtnorthrop Feb 1 '12 at 9:15
  • \$\begingroup\$ @mtnorthrop Do try with a new battery. If it solves the problem, the unit is defective. It is very important for multimeters to show the low battery indicator if the battery is low because low battery may result in incorrect readings and you'll have no way of knowing that they are incorrect. If the new battery doesn't solve the problem, then the meter is defective or there is a problem with its documentation. In either case, I recommend that you contact the manufacturer and ask them if the behavior is normal or not. \$\endgroup\$ – AndrejaKo Feb 1 '12 at 9:33

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