control a 9th valve with 6890N

[alba]

Hi all,

I'm trying to figure out how I could control a 9th valve (2-positions VALCO valve) with Chemsation and control its position (ON/OFF) during the runtime of the analysis (we already use the 8 valve controls available in the GC).

I have the impression that I should use a dynamic data exchange macro. Has anyone already handled this type of problem before?

Thanks in advance

[GasMan]

The only way that I can think of, is to have a free running program that will start your GC and also enable you to control the 9th valve via a time table.

You should also look at your present system. For example, if you have two 6 port gas sampling valves which inject at the same time, you could replace this with a 10 port valve that can be configured as a dual gas sampling valve. This would then free up a valve position. If you have a system with two liquid sampling valves, Valco do produce a dual LSV, again freeing up a valve position.

Another way to do the same thing if you have two valves actuating at the same time, is to 'tee' off the air supply to two actuators. By this I mean that you have the air supply to an actuator coming from a solenoid valve. You split the air line to two actuators, so that when you turn a valve on using the 'Valve X On' command, two valves will actually turn.

Regarding your thoughts on using a macro: user written macros will not run in ChemStation while the GC is running and collecting data. So as I see it, this would rule out you controlling a valve during a run.

One question. What are you using the Valve 7 and 8 positions to control?

Gasman

[alba]

Dear Gasman,

thank you for your answer. I think that the option of looking at the present system to free up a valve position is not possible. We have setup the system as in Sander et al. (2009) "A single gas chromatograph for accurate atmospheric mixing ratio measurements of CO2, CH4, N2O, SF6 and CO" (you can google it) and I have the impression that it is not possible (you can see there that V7 is used for a multiposition valve and V8 corresponds to 3 EVs that control sampled air nd ArCH4 flowing or not).

What you mention about user written macros was a doubt that I had. Then, one can only include macros during pre-run or post-run using the Run Time Checklist, right?

I need to use the 9th valve before the analysis because I'd like to "clean" the inlet tubing before the analysis with a vacuum pump. A 3-ways valve would be used to select between pump or GC. So maybe the fact of using the macro during the pre-run is not a problem. Which commands do you think that better fit for this case?

Thanks in advance for your help,

[GasMan]

alba,

Are we talking about the system set up in Holland by S.van der Laan? This is the only search answer that looks like the system that you describe.

If you are using this system, are you using the same valve time switching as shown in the paper?

I do not think that you can use the standard valve commands in a macro, as there is no Valve 9 set up in the 6890. I do not know if you can use RS232 in the GC version of the ChemStation. I have seen examples of RS232 communication for the UV/Vis version of the ChemStation. If this is possible, it should be easy to write a pre-run macro to control a Valco electric actuated valve via RS232. I will ask around.

If this is not possible in GC ChemStation, I might have a hardware solution, but this depends on your valve timing program.

Gasman

[alba]

Dear Gasman,

yes, the system is like the one from Van der Laan but we want to introduce a 9th valve to analyze batch samples collected in flasks. We want to use another valve to clean with a vacuum pump the tubing before the analysis of the flask in the GC. So the 9th valve should be active before the analysis itself.

I have seen in the Macro Programming guide (11/95, second edition) that there are several RS232 commands but in our Chemstation version they don't appear.

I have also seen in Chemstation CDs, in the UCL section, an utility for enabling the Chemstation to send and receive information over a serial interface ('Serial I/O from macros'). What do you think about this UCL utility? Would you use it or would you proceed differently?

I was thinking also about the possibility of writing a .exe program and then execute it as a pre-run macro.

If you could help me once again with your expertise I would really appreciate it.

Thanks a lot,

[GasMan]

alba

I have checked and found that the B and C versions of ChemStation do NOT support RS232 communication. Please contact me by email at Gasman41@gmx.de and I will then forward my idea to you that should enable you to operate the 9th valve.

Gasman