Is this a feature or a bug - Bside DMM - Page 1
Forum section: electronics / beginners

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: June 17, 2018, 12:58:09 pm
content: Hi, I recently bought a multimeter with a description in the instruction manuel. It reads something like this. On continunity check when you have less than 40 ohms the buzzer will sound and a green led will light. Between 40 and 60 ohms no buzz but a red led will light. Above 60 ohms nothing will happen.I check this and indeed this is what happens.The manuel says nothing more, since its not the instruction type, just the fact.My question is: what is the meter trying to tell me beside the obvious and how is it useful in finding faults in circuits?Informed responses please. Thanks.

author: wraper
author_rank: Unknown
timestamp: June 17, 2018, 01:09:29 pm
content: Quote from: joseph nicholas on June 17, 2018, 12:58:09 pmYou say obvious but apparently your ability to see obvious has some problems if you're asking such question. You can find connections and estimate resistance range without looking on a display of multimeter.

author: ebastler
author_rank: Super Contributor
timestamp: June 17, 2018, 01:36:29 pm
content: Quote from: wraper on June 17, 2018, 01:09:29 pmUh oh -- I am not sure whether that passes the OP's bar for an "informed response"...@joseph: It might be just me, but that requirement of yours comes across as a bit arrogant. "Posters less smart than me need not apply."

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: June 17, 2018, 02:28:18 pm
content: Sorry it was not ment to exclude any responses, just to have people who are interested in the post not respond but to follow along if interested.

author: Audioguru
author_rank: Super Contributor
timestamp: June 17, 2018, 11:57:30 pm
content: My meter beeps when measuring less than 40 ohms to warn me that the measurement is almost a short circuit.

author: Brumby
author_rank: Unknown
timestamp: June 18, 2018, 06:54:16 am
content: The feature is the continuity test function. Within that function, it has particular specifications.To use this feature you need to:1. Understand what those specifications mean2. Understand the parameters of the circuit you wish to testand3. Perform the test, applying the knowledge gained from 1 and 2 above to interpret the result.The question you might need to think about is "What is continuity?"If we just look at straightforward wire and cable continuity...* Is it zero ohms? Unless you're working with superconductors, that's simply not realistic.* What about less than 1 ohm? It gets a bit hard when contact resistance features strongly and you spend most of your time trying to make sure of a good connection.* Perhaps under 10 ohms? Now this is a bit more practical - but there may be long cables you want to test that might have this sort of resistance in them.Aside from these sorts of tests where "near zero" resistance is expected, there are several scenarios where there may be a deliberate low value, non-zero resistance introduced that still qualifies as part of the continuity path - or where a resistance under 40 ohms is "as good as" a short. Put simply, there has to be a line drawn somewhere and 40 ohms is a reasonable figure that, I have no doubt, has been learned from many years experience.The bottom line is exactly what I spelled out at the beginning - there is a specification and you need to understand that specification in order to interpret the result of any test, because sometimes the result is not black and white.

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: June 18, 2018, 11:58:03 am
content: Thanks for your thoughful replies. I was wondering if the makers of this meter had any specific idea of circuit theory when designing the meter. For example was the idea to give a green light to test long lenghts of cable for industrial applications. A red light for testing shorted capacitors and diodes during troubleshooting. It seems to spell out this difference in the manuel but not give detailed examples raises the question what utility does this have in practical applications.The meter does seem to be trying for industrial applications. It has a NCV feature. Maybe it was just something the manufacturer put there as a lark, just because they could.

author: wraper
author_rank: Unknown
timestamp: June 18, 2018, 12:32:51 pm
content: Buzzer for continuity testing is a standard feature for basically any multimeter besides the lowest of the low end. Often they also additionaly have display backlight turning on. Signaling for additional resistance range with different color is not that common, but if it has this feature, why not.QuoteYou are overthinking it. Also why manual should teach you how to do something like this? User manual is not electronics tutorial for beginners. What buzzer is supposed to do is beep on low resistance, how you will use it is on your own. What it helps to do is avoiding switching attention between what you are measuring and looking on the multimeter.

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: June 18, 2018, 05:48:51 pm
content: Quote from: wraper on June 18, 2018, 12:32:51 pmIt is a feature, I would guess. I will use the meter for continuity and see in the future how giving different color indications for the 40 to 60 ohm without a beep could be used. I will probabily stumble over a practical use for this feature.

author: Brumby
author_rank: Unknown
timestamp: June 19, 2018, 02:45:54 am
content: Maybe you will, maybe you won't.In all the years I've had DMMs I can't recall one event where such a feature would have been useful. If the buzzer doesn't sound and it's not open circuit, I'm going to be more interested in the resistance value measured.Don't get too hung up about this. Just know it's there and move on to more interesting stuff.

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: June 19, 2018, 10:40:35 am
content: Quote from: Brumby on June 19, 2018, 02:45:54 amWell I went back to the meter and checked it and it provides a resistance value on the display when in continuity mode up to about 100 ohms.So it does what you are interested in.

author: Brumby
author_rank: Unknown
timestamp: June 19, 2018, 02:34:05 pm
content: ... and if it doesn't, you simply switch over to the resistance ranges.