My Surf PI Null Offset on Pin 6 of 5534 is different when measured with multimeter & oscilloscope

[green]

first question to you. who from the geotechers did give you the suggestion to use voltmeter for null tuning?
mine? George? Carl? Eric Foster???
WHO?

Don't know about the Surf PI but step 5 of the Geotech Baracuda (RevA) build document suggests measuring the DC volts at amplifier out when adjusting null.

[Polymer]

The voltmeter reads the average signal which includes the offset when the coil is on and decay after coil turn off. You are reading the null after the decay with the scope.

Thank you green!

Of course ... how could I have not seen this

[kt315]

first question to you. who from the geotechers did give you the suggestion to use voltmeter for null tuning?
mine? George? Carl? Eric Foster???
WHO?

[green]

I am getting my Surf PI ready for testing with oscilloscope in the sea to see what happens when dunked.

I had adjusted the null a while back with a multimeter when I had no oscilloscope.

Now looking at the trace of Pin 6 I saw that the null is below zero by a whopping 320mV.

It also works the other way round. Adjust null with oscilloscope and have round 320mV on multimeter.

What am I not getting here? Does anyone have an idea what may be causing this?

I am really puzzled.

The voltmeter reads the average signal which includes the offset when the coil is on and decay after coil turn off. You are reading the null after the decay with the scope.

[kt315]

you measure impulse signal on DC range of your tester. yup? that is nonsense.
you also can not measure impulse signal nor in DC range neither AC range of your tester.

[Polymer]

I am getting my Surf PI ready for testing with oscilloscope in the sea to see what happens when dunked.

I had adjusted the null a while back with a multimeter when I had no oscilloscope.

Now looking at the trace of Pin 6 I saw that the null is below zero by a whopping 320mV.

It also works the other way round. Adjust null with oscilloscope and have round 320mV on multimeter.

What am I not getting here? Does anyone have an idea what may be causing this?

I am really puzzled.