Chromatography Forum

Hi All,

We are planning to automate a GC testing by connecting the Agilent GC 6890N to an Allen Bradley programmable logic controllers (PLC). Has anyone had any experience with PLC controlling of GC in terms of connection and remote start? Will appreciate it.

Leo

How is it different from a purge-and-trap or headspace sampler starting the gc? All is outlined in the 6890 manual.

You'll need to buy (or make, there's a pinout in the agilent 7890 advanced service manual, same pinout as 6890). If you're wanting the PLC to trigger the GC, you'll connect a digital output channel from the plc to this remote start cable. I think pins 1 and 3 are the ones that you need (been a while!). You can short the wires together to check and they should immediately start a run on the GC. Your PLC should basically be making a contact closure, so a relay may be necessary.

GCleo,

With an autosampler?

How many runs do you need? If less than about 9000 you could just run this as a sequence with 99 lines of 99 injections each. With a 5 minute run, that's about 35 days of analysis.

If more than 9000 or forever (ugly file structure after a while, God help you) then a simple timed contact closure might work for a lot less than a PLC (been there, done that, although in hindsight the customer would have been better served by the option above.)

Best regards,

AICMM

Dear all,

I am Looking to automate the 6890N wrt reading the "READY" SIGNAL.

I am refeerng to Pin 1 and 7 , is this a Potential free contact?

as per manual it says that is it is a TTL Signal .. in this case how do i connect to a PLC Digital input card?

or is there a TTL input card required to read the status.


Thanks
Hari

TTL signal output has , practically ,5 volts for a high output , and a 0 volt for low output.

Depending your input device , you may connect directly if it is TTL input , or you have to use appropriate buffer to adjust the voltage

thanks uzman for your post.

After my Post , after a lot of search.
I Discovered that it will be good to Wire a 5V DC Relay, for the Open Collector( TTL Signal ) for "GC Ready" Signal.

The Pullup Resistor Needs to beConsidered in to the Design as Well. I am just waiting for the Components to arrive so that i can test it live.

Regards
Hari

Dear hariprasad083,

No need to use a pull-up resistor , you may connect your relay between +5 volts supply and the open collector output.
Your relay will behave as pull-up resistor , but please consider the electrical current passing through the relay , it must not bigger than the stated current of output transistor.

Use a small current relay , around 20mA.

If your relay needs more current , you have to add a power transistor and necessary driving resistors to the output , but your signal will be inverted , i.e, high output will cause your relay off , low output will cause it on.

You may overcome this by using the normally closed contact (NC ) , instead of normally open contact ( NO ).