Products > Test Equipment
BM789 continuity behaviour
giosif:
Has anyone else noticed this rather annoying behaviour with the BM789 in continuity mode where, when connecting the probes to a part of a circuit where there is no continuity (or low resistance), it gives a short beep, but then stops.
If you then move one of the probes away from the part of the circuit to which it was connected, wait for a second or two, the connect back the probe, you get the short beep again.
To be clear, I'm not talking about parts of circuit which have capacitors connected.
This is annoying because, when trying to trace connections on a board, you get distracted by all these false positives and you end up having to keep the probes in a given location for longer, to make sure the meter beeps because of actual continuity.
In other words, the meter's fast response in continuity mode is being defeated by these (brief, but often) false positives.
Also, it is interesting that a BM257s or a 121GW do not exhibit this behaviour on the same board, same connection points, and same probes (i.e. these other meters don't beep at all in those same locations).
Could it be that the BM789 in continuity mode is too sensitive to the stray capacitance in the circuit and/or meter probes?
giosif:
Just adding another observation I've just made (again, with the BM789 in continuity mode): if I hold one of the probes in my hand (touching the metal part) and I touch the other probe to a piece of metal somewhere in my lab (I've used the boom stand of my microscope for this test), I also get the short beep.
LuisBe:
Sorry for my level of English, everything I write is done with a translator. I have just checked that my BM789 does the same as yours, both in the circuit and against the chassis of a remote and unconnected equipment. I have measured the resistance between the short beep points in the circuit and there is 1.35 Kohms.
BILLPOD:
I have a similar experience with my 121GW in 'reverse' continuity mode.
Actually it's called cable testing mode, but it's supposed to beep when continuity is broken. I get these short beeps when I test a suspected open in a DMM test lead :wtf:
siealex:
Is the continuity mode combined with the diode test mode? A short beep in this mode means a forward voltage drop between 0.1 V and 2.0 V for a normally functioning diode.
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