Section 6. Troubleshooting; Troubleshooting Guidelines; Baseline Problems; Baseline Or Signal Offset (Tcd) - ABB PGC2000 Operation And Service Manual

TROUBLESHOOTING GUIDELINES

This section provides troubleshooting information by category. Included in this information are
symptoms, causes, and suggested tests for further fault isolation. These tests are described in
Section 7, listed by Test Procedure (TP) number.

BASELINE PROBLEMS

Baseline or Signal Offset (TCD)

Symptom: Baseline (detector signal) is continually offset to the positive or the negative with no short
term drift up or down scale (see Figure 6-1). This is indicated on the graphic display, output recorder,
and the detector signal.
Background: A thermal conductivity detector (TCD) contains a measurement and reference filament
detector configured in an electronic bridge circuit. With no sample eluting the column, both
measurement and reference filaments are responding to carrier gas only. Therefore, the resistance
of both the measurement and reference filaments should be within one ohm of one another (cold) and
the detector in balance.
Causes:
1. Temperatures incorrect. Perform Test Procedure 30 (Checking Temperature Table Values),
steps 1 to 3 , and 8 to 12 to verify or change temperature settings.
2. No carrier gases applied to analyzer. Perform Test Procedure 1 (Carrier, Makeup, and Utility
Gas Supplies).
3. Large difference in reference and column carrier flow rate (example: reference 1 cc/min, column
20 cc/min). Perform Test Procedure 2 (Carrier and Makeup Gas Flow Adjustments).
4. Column broken or connection in column train disconnected, restricted or leaking. Perform Test
Procedure 1 (Carrier, Makeup, and Utility Gas Supplies) and Test Procedure 2 (Carrier and
Makeup Gas Flow Adjustments). If there is no carrier gas flow or the carrier gas flow is
restricted, perform Test Procedure 7 (Column Train Problems).
5. Defective carrier regulator. Perform Test Procedure 1 (Carrier, Makeup, and Utility Gas
Supplies), Test Procedure 2 (Carrier and Makeup Gas Flow Adjustments), and Test Procedure
4 (Carrier or Makeup Gas Regulator), as applicable.
6. Column flooded with liquid sample. Perform Test Procedure 3 (Sample Valve Leaking/Column
Flooding).
7. Detector balance adjustment needed. Perform Test Procedure 5 (TC Detector Balance).
2000-OSM, F1

SECTION 6. TROUBLESHOOTING

BASELINE
TIME
NORMAL
Figure 6-1. EXAMPLE OF BASELINE OFFSET
AMOUNT OF
OFFSET
BASELINE
TIME
OFFSET
6-1