External events on Agilent 6890

[larkl]

We have several other GC already configured this way (maybe not exactly the same way), but this one really has me puzzled.

We use an external box to purge the GC valves between runs. These contain a 110v solenoid which is driven by a 110v relay. We use a 24v signal from the GC to turn the purge on/off (hooked to the relay).

When I hook this device up to valve5 using the external events cable, it's on all the time, regardless of the valve setting (on/off). Checked it with a VOM and yes, it's 24V all the time.

The contact closures - events 7 & 8 - work as expected (on and off), but to use them, now I have to add another power supply (likely 12v).

Am I wrong, but I expected that the events 5 & 6 from the external events cable would provide 24v with the valve on and no volts with the valve off.

[GasMan]

Are you using both of the connections for the valve control at the socket? If you are only using one, and connecting the 'negative' line to ground, then you will have a problem. The 6890, as far as I can recollect, switches the negative line on and off, not the 24V line.

Gasman

[larkl]

Thanks gasman, but no, I'm checking with the VOM from the 1 & 3 wires directly off the cable.

[sllimbri65]

Are you using both of the connections for the valve control at the socket? If you are only using one, and connecting the 'negative' line to ground, then you will have a problem. The 6890, as far as I can recollect, switches the negative line on and off, not the 24V line.

Gasman

Gasman,
I am confused about the external and the internal valve drivers. I have tried turning the valves on and off but I only get a constant 24v when measuring from pin 1 and 3 on the external event cable for valve 5. The same when measuring pins 8 and 16 on the internal connection for valve 4. I am measuring between the pins with a vom as the sample run progresses through the event table where I tell it to turn on/off. Can you help me understand how these valve controls work? Thanks.