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Will this 2V signal damage my bench multimeter over time?
Amaruk:
I noticed something strange with my Siglent SDM3045X bench multimeter. It has an internal relay that is activated even when the meter is in manual range… The funny thing is that it happens at a voltage level that is not even a range limit and since there is no way (I know of) to prevent this relay from triggering will some signals damage the meter in the long run? Some say that relays have a life-span of 100,000 activations. If you measure a signal that crosses the 2V level four times per minute you will reach 100,000 activations in about 400 hours. Quite a lot of time for most users but if you have this meter in a production environment it might be a concern.
Demo: Here is a video in which I have a very slow sine wave signal (25mHz) with a voltage that goes from 1.9V to 2.3V (2.1V offset, 0.4Vpp, -90 degrees phase). I have my Siglent SDM3045-X in manual range (6V DC) so there should not be any range changes. However, as you see in this video, when the voltage passes 2.2V on the way up or 2.0V on the way down the internal relay is activated. Normal range changes when the meter is in auto-range are silent (600mV, 6V etc).
langwadt:
Relay lifetime varies a lot, there's how long the contact will last switching the rated load, and then there's how many times the relay can mechanically switch. Contact wear is probably not a big issue for a meter and some relays are mechanically rated for 10s of millions of cycles
you'd have to look up the specific relay.
Amaruk:
Good point. I just picked that 100K number as a wild guess. I am just curious, what is that relay doing? Why does it need to activate in the first place? Is it a firmware bug? I don't recall working with a DMM that has a relay like this in a manual range. Very strange... Anyone with ideas as to what is going on?
commongrounder:
I’m thinking that is the DC input impedance relay changing back and forth from 10G-ohm to 10M-ohm. 2-volts is at a range change point for this meter, I believe, and 10G-ohm can’t be used above that. There should be a menu setting to force the meter to stay at 10M-ohm all the time, which might stop the relay actuations.
Fungus:
--- Quote from: Amaruk on December 30, 2021, 04:08:46 pm ---I noticed something strange with my Siglent SDM3045X bench multimeter. It has an internal relay that is activated even when the meter is in manual range… The funny thing is that it happens at a voltage level that is not even a range limit and since there is no way (I know of) to prevent this relay from triggering will some signals damage the meter in the long run?
--- End quote ---
Yes, obviously it will.
(for some definition of "long")
The input jacks will also wear out as you plug in and remove the cables. And the USB socket - those type A sockets are only rated for 1500 insertions.
Best to enjoy it while you still can!
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