Question
When I do RMS measurements and an offset is applied, the result changes.
For example:
1 V/div, 0 V offset --> 15 mV
1 V/div, 5 V offset --> 35 mV
I could not see that effect on other scopes. What is wrong here?
Offset changes RMS measurement
Answer
This is not an error, it is caused from the frontend structure of the scope.
The offset voltage is applied at the input of the amplifier, see attached menu from the RTE/RTO/RTP
A change of the input voltage changes the operating point of the amplifier. As it is physically not possible to cunstruct an amplifier which is 100% linear, there is a small change of the measured RMS value.
The effect can be reduced:
- let the scope warm up for at least 30 minutes
- after 30 minutes start the self alignment (FILE --> Selfalignment)
