Pressure control

I tried to control the pressure by placing an electric valve between the DUO008b and the turbo pump, and switching the valve on and off with the TPG251 single gauge controller.

It worked, but it wasn't really stable, for example; setting HI en LO on the TPG251 to 6E-5 and 5E-5 resulted in a situation where the pressure dropped from 6E-5 to 1E-5 when the valve opened.

So then I connected the relais of the TPG251 to the external on/off function of the TCP121 turbo pump controller.

And that worked perfect!

Just switching the turbo pump on and off was enough to control the turbo speed, pressure was controlled within 10% for all desired values in the 1E-3 to 1E-6 mbar range.

The TPG251 has an external input for setting HI and LOW, should be easy to control it from the computer.