How to automate delay (skew) measurements between channels with tm_devices

[shalesrock]

Hello,

I'm trying to automate measurement of the delay (skew) between two channels on the MSO5B oscilloscope and having trouble finding the proper command syntax.

Setup: MSO5B oscilloscope with a 100 MHz signal on channels 2 and 3. Channel 1 in this test case is displayed on screen, with a low voltage signal, just to demonstrate that I don't understand the command syntax of the Delay command.

    from tm_devices import DeviceManager
    from tm_devices.helpers import PYVISA_PY_BACKEND
    
    with DeviceManager() as device_manager:
        device_manager.visa_library = PYVISA_PY_BACKEND

        scope = device_manager.add_scope("x.x.x.x")  
        print(scope)
    
        # Turn on channel 1,2,3
        scope.commands.display.waveview1.ch[1].state.write("ON")
        scope.commands.display.waveview1.ch[2].state.write("ON")
        scope.commands.display.waveview1.ch[3].state.write("ON")
    
        # Delete old measurements
        for i in range(3):
            scope.delete_measurement(i)
    
        # Adding measurements
        scope.commands.measurement.addmeas.write("DELay")
    
        scope.commands.measurement.meas[1].source.write("CH1")
        scope.commands.measurement.meas[2].source.write("CH3")

The result of this script is that I have two Delay measurements:

Meas 1: Channel 1 / Channel 2
Meas 2: Channel 3 / Channel 2

Questions:

How did Channel 2 get into my delay measurements? There is some modal behavior here that I don't understand that inserts channel 2 into the delay measurement.

What is the proper syntax for a delay measurement between two channels? Looking in the MSO5B Programming Manual:
[https://download.tek.com/manual/4-5-6-MSO-Programmer-Manual-077130516_RevA.pdf],

I see that there's some DIRECTION and EDGE commands that I'm not specifying anywhere.

I would appreciate any help with this command syntax, or pointing to a delay example (which I haven't found). I feel like I'm close to the solution, but maybe someone has already been there.

Thank you!

[shalesrock]

I just figured out that I can select the measurement channels for the delay measurement with a query command:

  # Initialize DELAY measurement
  scope.commands.measurement.addmeas.write("DELay")
  scope.query("measurement:meas1:source1 CH2") 
  scope.query("measurement:meas1:source2 CH3")

I don't understand why the query command should have any effect on the channel selection of the measurement.

[nfelt14]

The proper form would be the .write() method. .query() always sends a .write() before querying the device, but the .write() is all you need.

[shalesrock]

Oh thank you. It seems obvious now!