HP 5890 "pegged" signal

[EnvChemist]

I run PCBs on both a ECD GC 5890 and ECD GC6890.

On the 5890 both signals 1 and 2 are stuck at about 14800 (which is way over range). Someone said in passing that my signals are "pegged".

My questions are:

1. What does this mean ?

2. How does this occur (how do I prevent it)?

3. What do I do now ?

Thanks ...

[chromatographer1]

1. I think they meant to say that your detectors are registering their maximum signal output, IE the needle indicator of a hypothetical gague is fixed at the maximum on its scale, thus the needle is "pegged".

2. This occurs when something from the column is eluting and reacting with the detector causing a maximum output of the detector to occur (or the electrometer is stuck electronically).

3. What to do? Discover what is causing the high signal and remedy the problem so you can use the instrument.

best wishes,

Rod

[Schmitty]

If the 5890 is a dual ECD and both detectors are pegged, then it is probably a gas/filter issue. There are other possibilities, but this is the most obvious to me.

[Russ]

Have you tried capping the detector inlet and checking the signal with only the make-up gas going to the detector? This will eliminate any column or inlet issues. If you try this, give it some time "at temperature" to see if the signal will drop.

[vballchemist]

If the ECD's are >2 years old with medium usage or they have been at high temp with no gas flow then the cells may need to be refurbed: cleaned and/or foil replaced.

[EnvChemist]

Thank you all for your input . Turns out that the detector anode had shifted and was touching the detector surface such that the detector was grounded causing the signal to be unstable.

[Consumer Products Guy]

Grounded Agilent FIDs will give a similar pegged signal.

[EnvChemist]

Everyday you learn something new ...

Quick question though, the standing signal for my front detector is at 11.1 while the back one is at 5.8 .... does the difference matter ? A colleague told me that the signals should be about the same, but I have noticed that even as the instrument runs through it's program the signal on the back detector is usually about half the one on the front.