Teledyne 6200E - Sulfides Analyzer - Manual (Page 247)

Model 6200E Instruction Manual TROUBLESHOOTING & REPAIR
M6200E Rev: A1 247
11.2.1. Zero or Low Sample Flow
If the pump is operating but the unit reports a XXXX gas flow, do the following three steps:
• Check for actual sample flow
• Check pressures
• Carry out a leak check
To check the actual sample flow, disconnect the sample tube from the sample inlet on the rear
panel of the instrument. Make sure that the unit is in basic SAMPLE mode. Place a finger over the
inlet and see if it gets sucked in by the vacuum or, more properly, use a flow meter to measure
the actual flow. If there is proper flow of around 450-500 cm³/min, contact customer service. If
there is no flow or low flow, continue with the next step.
Check that the sample pressure is at or around 28 in-Hg-A (about 1 in below ambient atmospheric
pressure).
11.2.2. High Flow
Flows that are significantly higher than the allowed operating range (typically ±10-11% of the
nominal flow) should not occur in the M6200E unless a pressurized sample, zero or span gas is
supplied to the inlet ports. Be sure to vent excess pressure and flow just before the analyzer inlet
ports.
When supplying sample, zero or span gas at ambient pressure, a high flow would indicate that
one or more of the critical flow orifices are physically broken (very unlikely case), allowing more
than nominal flow, or were replaced with an orifice of wrong specifications. If the flows are more
than 15% higher than normal, we recommend that the technician re-calibrate the flow
electronically using the procedure in Section 6.9.9, followed by a thorough and regular monitoring
of these flows to see if the new setting is retained properly.
11.3. Calibration Problems
11.3.1. Negative Concentrations
Negative concentration values can be caused for several things:
• A slight, negative signal is normal when the analyzer is operating under zero gas and the
signal is drifting around the zero calibration point. This is caused by the analyzer’s zero
noise and may cause reported concentrations to be negative for a few seconds at a time
down to -20 ppb, but should alternate with similarly high, positive values.
• Mis-calibration is the most likely explanation for negative concentration values. If the zero
air contained some H
2
S gas (contaminated zero air or a worn-out zero air scrubber) and
the analyzer was calibrated to that concentration as “zero”, the analyzer may report
negative values when measuring air that contains little or no H
2
S. The same problem
occurs, if the analyzer was zero-calibrated using ambient air or span gas.
• If the response offset test function for H
2
S ( H2S OFFS 1 ) are greater than 150 mV, a failed
PMT or high voltage supply, or sample chamber contamination, could be the cause. Clean
the sample chamber according to Section 9.3.6.