Gentec ED-200 Optical Joulemeter: Oscilloscope Comparison

The little DSO-150 oscilloscope has a 1 MΩ || 20 pF input with a 200 kHz bandwidth that should be entirely adequate for the OMTech laser’s millisecond-scale modulation signals from the Gentec ED-200 Optical Joulemeter. There is, however, only one way to be sure:

Gentec ED-200 - scope test setup
Gentec ED-200 – scope test setup

The two scope inputs are in parallel, so the joulemeter over on the far right sees a 500 kΩ load, half of the specified 1 MΩ load, with at least twice the capacitance. If the two scopes display pretty much the same result, then it’s good enough.

A 50 ms pulse at half power looks the same on both scopes:

  • Gentec ED-200 - 50 ms - DSO-150
  • Gentec ED-200 - 50 ms - Siglent

A 50 ms pulse at full power doesn’t quite top out:

  • Gentec ED-200 - 11V 50ms - DSO-150
  • Gentec ED-200 - 11V 50ms - Siglent

Given that the pulse duration should be less than the detector’s 1.5 ms risetime, using a 50 ms pulse is absurd. Right now I’m just looking at the overall waveform and detector range, not trying to get useful numbers out of the poor thing.

All in all, the DSO-150 will do just fine.