Chromatography Forum

Dear all,

I would like to control the position of a 2-positions valve controlled through RS232 and Chemstation, and include the time when it changes in the runtime of the analysis.

I know how to move the valve but I don't know how to execute the commands in accordance with the runtime.

e.g. I would like to move the valve at 5.05 min after the run starts running and do other runtime tasks at the same time.

Could anyone help me? "ExecWait" ? But how to set the time specifically?

Thank in advance for your help.

Alba,

The only way that might work is for you to have a pre-run macro which starts an external program which can switch your valve at the required times. You cannot use a macro to function during a GC run. Is this still part of your original posting where you were trying to control 9 valves on the GC?

Gasman

Dear all (GasMan specially),

Thank you for your reply. Yes, it is somehow part of the post where I was asking how to control a 9th valve but thinking on another setup...

In fact, our many doubt appeared when trying to connect the following system to the GC:

Ambient air --> Through pump --> Through Multiposition valve --> pos. 1 -> air goes through the "GC"
--> pos. 2 -> air is "plugged"

We were thinking about the possibility of installing a 2-positions valve between the pump and the multiposition valve to let the pump work properly (keep pumping air and avoid overpressure) during pos. 2 period.

Do you think that this element (or similar) is compulsory?

Thanks a lot for your help,

What type of multiposition valve are you using, SD,SC,SF or ST?

Do I understand correctly that you would be sampling every other port, i.e. on a 16 stream valve, only 8 would actually be used?

Gasman

Alba,

One other thing that came to me, but this depends on what type of actuator you are using for your multiposition valve. If you are using what they call the 'micro electric' actuator, you have to program the motor for the number of positions. I have been told that it is possible to program a 8 position valve as a 16 position valve. This would mean that on position 1 you would be connected to a sample stream, but position 2 would be shut off as the valve would be halfway between ports 1 and 2. Thus all 'odd' port numbers would be samples and all 'even' port numbers would shut off.

Gasman

You state ChemStation, so I assume that you are using an Agilent HPLC system. If not: never mind !

There's an accessory external contact board available, installs into rear of certain modules. There are like 12 little wires, so 6 pairs (each pair is a numbered external contact #). These can be then programmed such as external contact #1 on at 5.05 minutes and external contact #1 off at 5.06 minutes , and the action can be a contact closure or DC voltage, you choose.

We've used this to zero/balance external detectors, and to initiate the flush in an Agilent 1047A external RID.

I have these part numbers, don't know if they've been updated: G1351-68701 for the board, G1103-61611 for the cable.

Dear all,

we currently use all possible control modules from the GC, so that's why I would like to control the other valve through RS232 in the PC. I think that the options you mentioned are not adequate for us, so we will just use a relief valve between the pump and the multiposition valve, since our pump can only work til 2.4 bar.

The option GasMan mentioned about the 8-ports valve and using it as a 16-ports valve is very interesting! We are in fact using a 16-positions valve (Valco; electrical actuator) with plugs on even positions.

Thank you very much for your help!