Chromatography Forum

Hello All,

I am a new user for 7890B GC. One of the FID detectors signal output became 8 million after I clean up the FID detector. Even when I take out the whole detector, the signal is still 8 million. Is that an electronics problem? Does anyone have a similar experience and any suggestions about how to fix it?

Another FID detector signal is stable when I conditioned the column first 30 minutes like always stay at 7.4. Then the baseline suddenly became very noisy to keep jumping between the range 12 to 14. Is that also the problem for electronics?

Thank you!

8 million signal means a short circuit .

If you removed the collector and still getting this signal , you may check the spring on the detector , it should not touch any metal part of the detector.

8 million signal means a short circuit .

If you removed the collector and still getting this signal , you may check the spring on the detector , it should not touch any metal part of the detector.

Except the concave portion of the collector. That is the only thing the spring should touch.

Also make sure you did not forget the teflon spacer that insulates the collector from the rest of the detector housing.

If the noise suddenly began on the second instrument check your gasses for purity and for any leaks in the supply tubing. Also make sure there are no fans or air conditioner outlets blowing on the detector, those can disturb the flame and cause noise too.

You probably have good gas but just be sure it is high grade carrier, hydrogen, air and makeup gas that is being used. I once went to help a laboratory that had a problem with an ECD they said had very little sensitivity, turns out what they though was a small signal was actually peaks that were interruptions in a maxed out signal on a chart recorder (very old instrument). When I looked at their setup they were using plain industrial grade hydrogen as their carrier, and actually had a section of rubber air brake hose from an auto supply company as an extension to make their gas lines long enough to reach the instrument.

A good grade of hydrogen carrier and fresh copper tubing gave them great signal and good sensitivity.

8 million signal means a short circuit .

If you removed the collector and still getting this signal , you may check the spring on the detector , it should not touch any metal part of the detector.

Except the concave portion of the collector. That is the only thing the spring should touch.

Also make sure you did not forget the teflon spacer that insulates the collector from the rest of the detector housing.

Thank you for all your suggestions! When I took out the collector, the spring touched nothing. The signal is still 8 million. Does that mean the short circuit happened with something else? How could I reset the signal? Should I unplug and plug the signal collector line from the electronic board? The big black line?

Thanks!

8 million signal means a short circuit .

If you removed the collector and still getting this signal , you may check the spring on the detector , it should not touch any metal part of the detector.

Except the concave portion of the collector. That is the only thing the spring should touch.

Also make sure you did not forget the teflon spacer that insulates the collector from the rest of the detector housing.

Thank you for all your suggestions! When I took out the collector, the spring touched nothing. The signal is still 8 million. Does that mean the short circuit happened with something else? How could I reset the signal? Should I unplug and plug the signal collector line from the electronic board? The big black line?

Thanks!

You may try to unplug and plug the socket(s) ( instrument power OFF ! ) , sometimes it helps ; if there is a loose contact.

If you have dual FID , you may also swap the amplifier boards , connected to main board.

Next step is to remove the signal bar. It simply unscrews from the electrometer can. It is rare but I have seen this be the cause.

Best regards,

Ive seen this. Usually just wiggle the castle around a little before screwing down. Watch the signal as you wiggle until it goes back to zero.