A question about clamp meter operation

[Mule]

Hello,

Every clamp meter I have ever used when on the DC current setting, the reading ranges by about 200mA when no conductor is inside the clamp. Some meter readings even range just by rotating the meter with the clamp closed.

Now my question is why is this? Especially in the case where you can rotate the meter and it changes the reading. Both these cases are without conductors inside the clamp. I am curious as to what is going on inside the meter.

Many thanks,

[Zbig]

Blame the Earth's magnetic field

[Jeroen3]

DC clamp meters use a hall sensor to measure current. This hall sensor measures magnetic field.
Due to this, they are especially vulnerable to permanent magnets and transformers.

They often are off by a huge amount if the core of the 1:many transformer (the clamp) does not close properly. They can also be magnetized by high dc currents or long time use. Use it on AC to remove this offset.

[Zero999]

Use the rel. or zero function with no conductor in the clamp, to make sure the reading is zero before using it. If the meter doesn't have a zero or rel. function then it's crap: you'll just have to remember the figure or write it down and deduct it from the reading.