Chromatography Forum

Hi Everyone,

I performed a quick forum search and did not seem to find anything relevant. I apologize in advance if this has been asked before.

Our lab had a series of power outages a few days ago and since that time we have been having trouble with the air flow on our 7890 GCs. A quick investigation into the issue makes it appear as if the pneumatics needs to be zeroed and recalibrated. I believe I was told that when the air flow is off (re: valve at cylinder has been shutoff), the GC is reporting an air flow of ~40mL/min.

I am unable to locate information regarding how to zero and recalibrate. I understand that the pneumatics/transducer may be damaged, but recalibration is the first step.

We have several 7890's in our lab and it appears that two have been taken out and are presenting the exact same problem with respect to the pneumatics for the air.

Any help y'all could provide would be greatly appreciated.

The following may help and is from the 7890 Advanced user manual

To zero a specific flow or pressure sensor
1 Press [Options], scroll to Calibration, and press [Enter].
2 Scroll to the module to be zeroed and press [Enter].
3 Set the flow or pressure:
Flow sensors. Verify that the gas is connected and
flowing (turned on).

Pressure sensors. Disconnect the gas supply line at the
back of the GC. Turning it off is not adequate; the valve
may leak.
4 Scroll to the desired zero line.
5 Press [On/Yes] to zero or [Clear] to cancel.
6 Reconnect any gas line disconnected in step 3 and
restore operating flows
To zero all pressure sensors in all modules
1 Press [Service Mode], scroll to Diagnostics, and press [Enter].
2 Scroll to Electronics and press [Enter].
3 Scroll to Pneumatics and press [Enter].
4 Disconnect the gas supply lines at the back of the GC.
(Turning them off is not adequate; the valves may leak.)
5 Scroll to Zero all pressure sensors.
6 Press [On/Yes] to zero or [Clear] to cancel.
7 Reconnect all gas supply lines and restore operating
pressures.


Gasman