Engin-X stress rig: waveform generator issues

From JK (Engin-X):

> - [...] When the wave amplitude is set correctly, and the test therefore runs as expected, the value displayed in the IBEX block is misleading. As it stands now, the units here should be ignored, and the value is simply a fraction of the full scale of the transducer for the selected control mode. For this experiment in Strain control we were using an extensometer with +/- 20% strain travel, and the amplitude number displayed here was 1/20 of the actual set amplitude. I think in principle this bug would also be present for the other control modes.
> - Once the waveform generator has been started and stopped (with the GUI Stop button) once, the cycle count and (I think) amplitude can no longer be changed. Resetting the IOC [...] seems to restore the expected behaviour though.
> - Changing the control mode will in principle update the displayed units for the wave amplitude, but it seems to display the units for the mode that was set immediately previous to what the actual mode currently is. Setting the desired control mode to the same mode twice thus ensures the amplitude displays the correct units. I’ve not investigated if this is merely a display issue for the units, or whether the rig actually does the wrong thing if you try and do a waveform with the wrong units set for the amplitude.
> - The amplitude showing the wrong units can also happen under other conditions if the rig changes mode by any mechanism other than the drop-down combo box, e.g. because a limit is tripped or the rig is manually turned to low power. Typically these put the rig in Position control as that is deemed the safest and most predictable control mode. Again, I’ve not tested the true implications of the incorrectly displayed units to see if it affects the actual rig behaviour.