Channel Alignment

Measuring the response of 2 photodiodes to high speed laser pulses of approx 30ns duration with a CS328A
The signal levels are quite low, of the order of a few too tens of mV

If I switch the amplitude magnification of a channel from 2mV/div to 1mV/div this introduces a miss-alignment between the timing of the pulses on channels A & B of the order of 200nS if the second channel is at a magnification >1mV

Is this change in timing expected behaviour when the amplitude magnification of a channel is changed?

Measuring the response of 2 photodiodes to high speed laser pulses of approx 30ns duration with a CS328A The signal levels are quite low, of the order of a few too tens of mV If I switch the amplitude magnification of a channel from 2mV/div to 1mV/div this introduces a miss-alignment between the timing of the pulses on channels A & B of the order of 200nS if the second channel is at a magnification >1mV Is this change in timing expected behaviour when the amplitude magnification of a channel is changed?

It is not expected behaviour! Seems you have discovered a bug which we did not know about. We have been able to repeat it here, do not know why it is happening but have confirmed it is in the firmware and added it to our list of things to investigate.

The work-a-round is to leave the scope display on values - say 5mV - that do not cause the problem to appear and then drill in using the tracking graph as per the attached.

Alternatively, if you must work in the scope graph, you could set the Channel Time Alignment to compensate but that does have the risk of forgetting it is there.

It is not expected behaviour! Seems you have discovered a bug which we did not know about. We have been able to repeat it here, do not know why it is happening but have confirmed it is in the firmware and added it to our list of things to investigate. The work-a-round is to leave the scope display on values - say 5mV - that do not cause the problem to appear and then drill in using the tracking graph as per the attached. Alternatively, if you must work in the scope graph, you could set the Channel Time Alignment to compensate but that does have the risk of forgetting it is there.

Thanks for the confirmation & workarounds

Some other features of the issue I noticed
It does not matter which channel is set lower the miss-alignment will occur
The miss-alignment can be triggered at higher vertical scales i.e 2mV if the scope graph display vertical size is reduced

Thanks for the confirmation & workarounds Some other features of the issue I noticed It does not matter which channel is set lower the miss-alignment will occur The miss-alignment can be triggered at higher vertical scales i.e 2mV if the scope graph display vertical size is reduced