FID has Unusual High Signal Output

Answer

This Information Applies To: Agilent GC Systems

Issue

GC Flame Ionization Detector (FID) Baseline Output stuck at more than 500,000 pA up to 8 million counts.

Background

If the FID interconnect spring is bent, damaged or has bad contact with FID base, it can cause a short circuit in the FID signal circuitry. The consequence is an extremely high baseline signal output. 

Requirements

Cool the detector to ambient temperature, then turn off the GC before proceeding to check condition of FID interconnect spring.

Items Required

• Lint-free gloves

• T- 20 Torx screwdriver

• 5/16- inch wrench

• Clean cloth   

  Warning: The oven or detector may be hot enough to cause burns. If the detector is hot, wear gloves to protect your hands.

   

  Caution: To avoid contaminating the FID, wear clean, lint-free gloves when handling the collector assembly.

   

  Caution: Avoid exposure to voltages on the instrument, or damaging the instrument while performing these steps by switching off the instrument before performing this procedure.

   

   

Steps to Follow

1. Disconnect the ignitor cable assembly. See Figure 1

   
   
   Figure 1. Ignitor Cable Assembly
   
   

2. Loosen the ignitor with a wrench as shown in Figure 2. 

   
   
   Figure 2. Disconnecting the ignitor
   
   

3. Turn the nut counterclockwise by hand. Remove the ignitor and copper washer. Place it on a clean cloth.

4. Remove the three screws that hold the FID collector assembly as shown in Figure 3. 

   
    
   Figure 3. FID collector assembly
   1. T- 20 Torx Screws, 2. Collector Assembly, 3. Detector Weldment, 4. Interconnect Spring
   
   

5. Remove and lift the collector assembly and you will see the interconnect spring underneath (see Figure 4). 

   
   
   Figure 4. Removal of Collector Assembly 
   
   

6. Visually inspect condition of the interconnect spring. Make sure that the interconnect spring is not damaged, bent, or dirty. Otherwise, contact your local Agilent service representative for further advice. 

7. If the collector assembly is properly assembled, the longer part of the collector body must be facing down (see Figure 5).   

   
   
   Figure 5. Collector body
   1. Long end 
   
   

8. Place and screw back the collector assembly onto detector weldment. The interconnect spring should fit in snugly at the groove of the collector body, use Figure 6 as reference. You will hear a "tack" sound that indicates the spring is sitting snugly at the groove.

   
   
   Figure 6. Location of groove in collector body (disassembled) 
   
   

9. Power on the GC to check the output.

10. If signal output remains unusually high, contact your local Agilent service representative for further advice. 

Learn how to effectively operate your Agilent Gas Chromatography: GC-9000-1250s - Agilent Intuvo 9000 GC Flame Ionization Detector (FID) Theory and Operation GC-7890-2250s - Agilent 7890 Series GC: Flame Ionization Detector (FID) Maintenance and Troubleshooting e-learning courses available from Agilent education