supply voltage PSI module


I have a qustion.

how can i see the supply voltage on the module PSI ?


  • Hi Azrael,

    Could you provide more detail such as instrument model and specifically what you are asking for?



  • Hi James. Sorry. I mean the EPC pressure module in 7890. I am interested in module diagnostics. it is convenient to observe the change in voltage on the module, whether it is open or closed, in what state it is.

  • Hello Azrael,

    Sorry that I interfere.


    It would be helpful to find out which specific problem is present?
       (e.g. pressure not stable, not achieved, etc. + EPC values)



    Over the years, my EPC troubleshooting support has shown the following:
    From an electronics enthusiast's point of view, I understand the voltage monitoring desire; but from a supporter's point of view, I have to look at the whole system.
    This entire system consists of EPC, inlet, tubes & fittings; where voltages cannot detect a loose fitting or indicate clogged tubes/valves by sample residue. Only pneumatic tests are useful for checking an entire inlet system.

    There are a few ways to do pneumatic P.M. / checks (for leaks or restrictions):
    - P.M. on split vent line & trap, which can clog with samples.
       ~ the split tube can be easily changed or even flushed.
       ~ the cylindrical split vent trap can only be changed (please do not try to clean it!)

    - Since leaks are a regular companion, regular EPC checks are recommended:
       ~ Pressure checks (SL Quick check or pressure decay test)
       ~ Restriction test
     Details on how to carry out pneumatic checks: call up the link at the end of this text.


    - In RARE cases, the flow measurement of a valve is also helpful, using an external flow meter:
       ~ Split vent out:
          * If EPC is in Splitless mode (+ 2x prep run), no flow should be measurable from this outlet.
          * If a flow can be measured, there is a leak on the valve. (Similar to brake pads on the car, these are also consumables.)

       ~ Septum purge:
          * With the 7890 this is a method parameter: is the displayed actual SP flow = the externally measured flow?
          * Example of a defect (that occurs extremely rarely): if the setpoint is 3ml & the measured flow is approx. 30ml, then the valve is usually defective.

       - In the event of blockages or leaks: sorry, but voltage monitoring does not help to observe the whole inlet system.
       - Only helping step:

          ~ pneumatic checks, it's the same what service engineers typically do on site.
          ~ Step-by-step description for leak- & restriction checks:


    regards, M

  • hello mhardacker !

    thanks for your answer and for the link!

    I was interested in how a work EPC module. And I think what watching the supply voltage gives me more information about the state the module. I had one problem with FID detector. A new device 7890 with two FID detector. and on one detector the flame began to go out, and then stopped igniting. how can this be on a new detector? I did not have a flow meter and could compare the supply voltages on the valves of both detectors and roughly estimate the state of the gas flow. There is no pressure control sensor on these modules for the detector (or maybe this is not the Electronic Pressure Control module?). I checked the candle, the flow ratio is correct, but the flame still went out. then I disassembled the detector and reassembled it. and it all worked. and now I think the reason was poorly twisted details. because when I took apart the detector I unscrewed the head too easily. And hydrogen gas seeped into the gap and, accordingly, the flame was extinguished. What is your opinion on this?

    regards. Azrael

  • azrael,

    please, for future communication, as this will save us all time! in in initial/first  mail:

    • what exactly is the HW? (here it would be GC 7890, FID EPC ...)
    • For efficient problem solving, the REAL problem should be named. If there is also a specific error message: also helpful / also submit.
    • Especially when it comes to electronics or FW background information, Agilent sees many areas as internal use or even confidental. That is why several voltage or electronic valve questions cannot be answered.




    • FID vs car: if a new car is driven too hard / too much without the necessary maintenance: then there are problems there too!
    • voltages on valves tells me nothing about the flow! This COULD ONLY be helpful with mass flow controllers.
    • Diagnostic lab tools
      a) Flow meter: if you want to do a good diagnostic of your own in the lab, you MUST have a (simple) flow meter!

          b) highly recommended a leak detector (He, H2 use)
             Not cheap, yes, but it will save hundreds of hours of work over the course of 10 years! Thus the product is a very inexpensive time saver.          =>


    ------------------------ GENERAL TROUBLESHOOTING:

    Typical causes & checks for jet based burner (here FIDs):
    * Measurement of gas flows (flow meater + flow adapter: )
    * JET clogged (especially by column film), do:
       ~ jet restriction test
       ~ change jet (in SOME cases a jet cleaning is possible)
    * Colum: cut off the end, clean & reinstall
    * dismantle the detectors to remove problem deposits (column film)!
    * LitOffset: if the signal value falls below a certain value, the flame switches off automatically
    * The EPC front pressure (wall supply) of the burner gases must be sufficiently good
    * gas generators: if other consumers draw gas, the pressure / flow at the local GC may be too clean: shutdown of FiD

    Agilent has wonderful manuals on this:
    GC Troubleshooting manuals => Jet restriction tests


    Maintaining the FID


    FID Maintenance Kit Instructions


    FID Ignition Problems. Flame will not light or will not remain lit =>


    Good community FID article, by searching:
       FID flame cannot ignite // FID shut-off frequently during operation .... etc



    * If lab users get stuck, they should consider visiting a local service on site.

    * When I solved a problem, I was proud / happy & usually never asked others about the possible reasons for my fix.


    regards, M

  • mhardacker, 

    no problem. I raised this topic before I solved this problem and returned to it. and now I was only interested in opinion or maybe someone had a similar experience. I'm interested. and I didn't ask about the possible reasons for my decision. and of course I am proud that I solved this problem.


  • This question has been marked as assumed answered.

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