Does your multimeter have wrong connection alarm? Try this. - Page 1
Forum section: electronics / projects

author: Lightages
author_rank: Unknown
timestamp: January 20, 2013, 03:00:36 am
content: I was playing around with measuring burden voltages and such between my meters and found potentially dangerous flaw with at least two meters. The wrong connection warning can be fooled to not sound even though the dangerous connection exists!To test if your meter has this flaw, put your leads into the input jacks to measure current and then select anything other than current measurement function. You should of course here and/or see the warning that you have the leads connected incorrectly. Now connect a voltage to the leads, 1.5 volts worked with mine, and try both polarities. The warning might stop on one of the polarities. Of course if you were measuring a voltage of this polarity and then moved the lead to a current measurement jack the alarm will not sound.This error will only happen with the input jacks that use the split jack type, not with optical sensing.Please try this with your meter if it has this flaw and report it here.

author: David_AVD
author_rank: Super Contributor
timestamp: January 20, 2013, 03:43:00 am
content: Just goes to show that people need to think about what they are doing when using a multimeter. I guess a wrong connection/setting warning is nice, but hardly what I'd call an essential feature.

author: Lightages
author_rank: Unknown
timestamp: January 20, 2013, 05:55:32 am
content: I realize that nothing is foolproof but when a feature that is added to help warn a person of a danger and the feature is not reliable it can add to the danger by making the user more complacent rather than safer.

author: iloveelectronics
author_rank: Frequent Contributor
timestamp: January 20, 2013, 06:14:44 am
content: Quote from: Lightages on January 20, 2013, 05:55:32 amI haven't tried this on my meters but did that fool your Brymen 869?

author: Lightages
author_rank: Unknown
timestamp: January 20, 2013, 06:21:00 am
content: Yes it fooled my Brymen BM869 and my Uni-Trend UT71E.

author: Wytnucls
author_rank: Super Contributor
timestamp: January 20, 2013, 07:15:50 am
content: I'm not sure I understand your line of thinking.The aural warning is there to warn you that one of the leads is still in an A/mA jack when the range switch is moved out of position, BEFORE connection to a live circuit.If your leads were still connected to a high power circuit, warning or no warning, your fuse would have ruptured before you can react to correct the mistake.After current measurement, one should ALWAYS disconnect the probes from the circuit, BEFORE moving the range switch.

author: krish2487
author_rank: Frequent Contributor
timestamp: January 20, 2013, 07:16:56 am
content: I blew up a Fluke 15B exactly like that..Ouch!!Was in a preoccupied state when i was asked to measure the mains by grandfather.I connected the leads to the current inputs and went to measure mains voltages and no sooner than I put the leads in, the HRC fuse blew and the MCB in the house tripped.Thankfully flukes are more idiotproof than foolproof.It saved one idiots(me) life..

author: Lightages
author_rank: Unknown
timestamp: January 20, 2013, 07:29:07 am
content: Quote from: Wytnucls on January 20, 2013, 07:15:50 amYes for the majority of the times you are likely to make this error that is going to happen. But let's face it, people make errors. One could be measuring some source that cannot supply enough to be dangerous but enough to eventually blow the fuse. No danger but a cost in replacing the fuse. Or maybe you are troubleshooting something and you are measuring where there is no protection for the circuit under test and it could get damaged if left across a 0.1ohm shunt for too long. Many scenarios are possible so it is good to know if your meter has this flaw so you then can not trust the warning alarm.

author: Unknown
author_rank: Unknown
timestamp: January 20, 2013, 01:15:33 pm
content: This sounds far-fetched to me. While still in current mode, you connect the leads in a manner that can damage the DUT, and then the DMM is at fault if it doesn't warm you when you eventually switch it to voltage mode. Most likely, the damage is already done by this time. Not much the DMM can do if you screw up the connections while the meter is clearly in current mode.

author: Lightages
author_rank: Unknown
timestamp: January 20, 2013, 10:52:58 pm
content: OK, in real practical examples.1. You have a circuit that can blow the fuse(s) after a few seconds. You don't notice the wrong connection and then you might have some expensive fuses to replace.2. You have a circuit that cannot stand to be shorted and you have the leads in the wrong jack, a few seconds later you have the magic blue smoke.In the above cases if the alarm was not disabled by the voltage you might have time to disconnect the leads before anything was blown, if you hear the alarm.I bet many people have and will move leads from one jack to the other without disconnecting the other ends first. I see it frequently on videos here and other reviews. Yes, it is the fault of the user causing the problem not the warning alarm not working, I agree. I am just trying to point out a flaw in the jack warning system that some might not be aware of.

author: David_AVD
author_rank: Super Contributor
timestamp: January 21, 2013, 12:12:23 am
content: Quote from: Lightages on January 20, 2013, 10:52:58 pmThey are doing it wrong then.

author: poodyp
author_rank: Regular Contributor
timestamp: January 21, 2013, 07:48:45 am
content: I'm confused... I'm supposed to put the leads in the amps connection, switch to volts/resistance/whatever, and apply 1.5 volts? That would take several amps...And if the connection is already in the amps jack and I was measuring something, why would it matter if it beeps or not?

author: Lightages
author_rank: Unknown
timestamp: January 21, 2013, 10:49:58 am
content: Use a small capacity cell or current limited power supply so you don't blow your fuse.If you don't think it is worth worrying about, don't worry about it. Just sharing information.

author: David_AVD
author_rank: Super Contributor
timestamp: January 21, 2013, 12:15:39 pm
content: What I think we're all getting at is that it's the method (of using the tool) that needs adjusting, not the tool itself.

author: rsjsouza
author_rank: Super Contributor
timestamp: January 21, 2013, 01:07:37 pm
content: I think that Lightages has a point: the probe detection should be active irrespectfully of the input applied...However, I agree with others that obviously procedure is fundamental in this case, and switching probes with them connected to the circuit is unsafe and the manufacturers are probably not considering this as a very frequent event (or simply don't care).Well, anything that helps save an expensive HRC fuse from blowing out is a welcome plus. I (and probably others here) come from the analog era, where most of the protection of a multimeter came from yourself and not the equipment - time of unfused high current inputs, unprotected input resistance and no-negative measurements (which would destroy the needle depending on conditions). That, added to the fact these things were ridiculously expensive and labs would only have one or just a handful, and you surely pay a lot more attention to what you are doing.I have the impression that nowadays they have much more protection and are so cheap (comparatively) that it allows for people to "relax" when dealing with procedure... Just as wytnucls said in another thread: "most of the accidents have happened with the best equipment available, often used incorrectly, in an industrial environment. The simple advice is 'Know the limitations of your multimeter and be aware of the potential dangers before you connect your probes to anything'"

author: WV1800es
author_rank: Contributor
timestamp: January 21, 2013, 02:59:57 pm
content: One multimeter I got recently (the HoldPeak 760D) physically blocked the Amp/MA inputs when the dial was turned to a different range. By the same means, you could not switch to a voltage range when the test leads were connected to the Amp/MA jacks. Interesting bit of 'shuttering' in the design, coupled to the range/function switch.