I have an older digital multimeter, a Radio Shack 22-163. It uses two
The device wasn't malfunctioning in any way, but I decided to do a
visual inspection of the batteries powering this device.
One of the two sets of terminals was corroded, but not badly.
1) Why does one set of terminals corrode, and the other does not?
I decided to remove the batteries. Nothing is obviously wrong, they're
not leaking that I can tell. They're actually in good shape considering
they're a couple years old.
2) I replaced the batteries with another set that I had lying around,
now the unit "resets" itself, and then proceeds to act normally whenever
I power it on. All the LCD lights blink, and the beeper, which I
normally keep off, and then the device normally remembers that it was
off between usage, and remains off, now is back on every power up. It
is obviously defaulting.
Now, why is all this happening, and how can I fix it?
Sorry for the delay, problem with the news sever.
Yes to all. I suspect (but can't confirm) that the corrosion on one of
the terminals is interfering (why is there corrosion on one set of
terminals, and not the other, again?) but the corrosion is clearly not
preventing electrical signal.
Corrosion will only occur at the anode. You often see this with car
batteries (not as much as it used to be.
The terminals should be well cleaned-try a bit of emery cloth to get
clean shiny metal as there is likely a bit of stuff on the contact
surface which puts some resistance into the meter supply circuit,
reducing voltage sufficiently to cause problems. I've had a blood
pressure meter get quite unreliable in a similar situation.
If the meter is to be stored for a long period, take the batteries out.
Ok, but this doesn't answer why the unit resets itself at every
power-on, and what I can do about it. Electrical contact is definitely
happening, because the unit powers on just fine.
Galvanic Corrosion explains why one set of terminals would corrode and
the other does not, if they were different materials, but in this case,
they are the same material.