23-08-2017, 04:57 PM
Yes, all the Aneng meters do this - I discovered this a few weeks back during another investigation that I'm in the middle of writing up. It seems that the output path (needed for injecting current into resistors, diodes and capacitors) is switched into circuit when the meter is switched off. This means that the PTC and the two transistors configured as a high speed, low leakage clamp are across the terminals.
That explains why if you try to measure the resistance between the terminals, you'll get different results according to the meter you use to test, and its open-circuit voltage.
As to why they do this, your guess is as good as mine, but one suggestion was to stop static damaging anything (though I don't buy that because the meter is pretty robust in all of its modes, as we know). It could be an intentional feature - lots of DMMs have a low-Z mode - but if so, why is it undocumented?
It's obviously good practice to not change the function switch while connected to a circuit, but one could definitely be forgiven for thinking that switching the meter off ought to be OK
I'll be honest - I let them auto power-down. I figure that the current drain is so small that I might as well save wearing out the switch contacts!
That explains why if you try to measure the resistance between the terminals, you'll get different results according to the meter you use to test, and its open-circuit voltage.
As to why they do this, your guess is as good as mine, but one suggestion was to stop static damaging anything (though I don't buy that because the meter is pretty robust in all of its modes, as we know). It could be an intentional feature - lots of DMMs have a low-Z mode - but if so, why is it undocumented?
It's obviously good practice to not change the function switch while connected to a circuit, but one could definitely be forgiven for thinking that switching the meter off ought to be OK
I'll be honest - I let them auto power-down. I figure that the current drain is so small that I might as well save wearing out the switch contacts!
