DMM 'OL' Displayed

[danechip]

Morning all. Quick one to settle. 'OL' displayed on a DMM when reading Voltage. What is OL? I believed it to be Over Limit. Mate suggests Open Loop.

Thanks in advance. Dan.

 

[securespark]

In my experience it has meant Over Limit.

However, depending on the meter brand, when measuring continuity, no continuity can be displayed as "Open Loop" or "1", or sometimes even the infinity symbol (a sideways "8").

Check your meter instructions.

 

[ericmark]

Never managed to get OL shown on voltage range on my meter. Ohms and diode test yes but not volts. I suppose diode test is volts in a way. But an open loop means it is over the limit any way so what does it matter. Over limit would seem a good phrase to use.

 

[stillp]

Mine is "OverLoad" according to the (Taiwanese) instructions.

 

[JohnW2]

Never managed to get OL shown on voltage range on my meter. Ohms and diode test yes but not volts.

Maybe you have an auto-ranging meter? With a traditional switched-range meter, it's the easiest thing in the world to get an "OL" display - this is what happens if one tries to measure 9V on the "2V range" ....

Kind Regards, John

 

[PBC_1966]

Some display an "OL" indication for overlimit/overload, some displays have a tiny "OVERLOAD" or similar message appear above or below the main readout, others just use something like a single "1" displayed at the far left with the rest of the numeric display blanked.

 

[JohnW2]

...others just use something like a single "1" displayed at the far left with the rest of the numeric display blanked.

Indeed, I have some meters which do that.

Kind Regards, John

 

[ericmark]

Not fully auto ranging but years of using the older meters has taught me start at highest range and move down. So would not attempt to turn to 200 volt range if the 600 volt range showed over 200 volt.

However with the ohms range one does tend to remove leads while meter still turned on so one sees the OL display.

Where the new meter has caught me out however is unknown voltage I would measure set to AC this worked OK with the old AVO Mk8, however with the digital meter it can show 0 or very low volts when it is quite a high DC voltage. As a result I never use my multi-meter to prove dead.

 

[danechip]

Thanks all. I've shown him this but still thinks he's still right. I'm sure my fluke meter years ago said Over Limit in the instructions too but I can't find a copy. And yes, my cheapy ones now just show '1'.

 

[PBC_1966]

Not fully auto ranging but years of using the older meters has taught me start at highest range and move down.

Indeed, that was always the recommended procedure in order to safeguard the meter, and no doubt those of us who grew up in that time just do that as a matter of course.

However with the ohms range one does tend to remove leads while meter still turned on so one sees the OL display.

And in that case, one could argue that "Open Loop" might well be an appropriate description with an open circuit and inifinite resistance. But clearly it's not when it comes to measuring voltage or current.

Where the new meter has caught me out however is unknown voltage I would measure set to AC this worked OK with the old AVO Mk8, however with the digital meter it can show 0 or very low volts when it is quite a high DC voltage. As a result I never use my multi-meter to prove dead.

I still have, and use, an Avo 8 Mk. III as well as a Heavy Duty Avo and a couple of the "lesser" models such as the Minor. As wonderful as digital meters may be for some things, there are cases in which they're not the best choice. Adjusting for peak or null is another example, as is watching slowly varying voltages in which a digital is always playing "catch up" due to the sampling.

 

[JohnW2]

Thanks all. I've shown him this but still thinks he's still right. I'm sure my fluke meter years ago said Over Limit in the instructions too but I can't find a copy. And yes, my cheapy ones now just show '1'.

Suggest to him that "Open Loop" really makes no sense in relation to voltage or current measurement (although, as has been said, it could for resistance measurement) - and, if he still doesn't accept it, ask him what on earth "Open Loop" could mean in relation to voltage or current measurements.

Kind Regards, John

 

[ericmark]

I remember being given a task in university to demonstrate how a PLC could work. The idea was to give the school children some plastic animals which they could place on a conveyor and it would identify which one each model was. We expected out of line, even backwards what we had not done was expect them to have one animal riding on the back of another.

I think we all expect people to act as we would until shown they will not. So we expect things like starting on the high range and working down. Also starting with AC volts. However when I went to do an "A" level it was not that a student had made an error and tried to measure amps instead of volt but how many made the same mistake.

I was not in teachers good books when I tried to comfort a student by saying since so many had made the mistake it was clearly a teaching error. But the teacher has clearly thought the students would not be that daft.

Today you may get away with using a meter set to 12 volt and putting it on a 230 volt source, but in my day either a fuse would blow or more likely the meter would burn out. Does it really matter is OL means overload, open loop or simply error. Only in the ohms range should you see it.

As said some cheap meters just show 1 and if I was a manufacturer I would look as what the chip can display and if the chip has the option to display ERROR great but if not then you select something one hopes will not be seen as a reading. The letters shown will likely mean something in the language of the chip designer or maybe even some dead language like Latin.

I remember arguing over what DOS mean, my early computer books called is a device operating system seemed "operating system" was the last two letters but as to if disk or device was first letter seemed to cause no end of arguments. I decided since the first computers did not have disks the used reel to reel tape or even a cassette tape disk seemed unlikely device seemed much more likely. But there were loads of book with both meaning from manufacturers.

But did it really matter what many called DOS others called CLI or command line interface and if you had a windows 95 or latter operating system then DOS games did not work did not really matter what it stud for.

So yes likely does mean over load but why worry what it means? Just try to ensure it is not displayed.