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Maintenance Series 4060
66 Teledyne Analytical Instruments
attempt to evaluate performance on sample gas. If analyzer sensitivity is
questionable, use the span gas. For all other evaluations, use the zero gas
and low range for maximum sensitivity. The important consideration is
to control as many variables as possible. Using cylinder-supplied gases
of known hydrocarbon content eliminates the possibility of introducing
an unknown variable.
Do not overlook the seemingly obvious. Check to see that power is
available for the instrument (and of the proper voltage, etc.), and that
connections are correct. Also verify that support/calibration gases are
not depleted.
5.1 Measuring Circuit Electrical Checks
If the analyzer performs erratically on span gas, the trouble can be
related to either the integral gas control systems, or the electronics. To
isolate the problem, the two systems must be separated. To isolate the
electronics, employ the following procedure:
Open the door to the analyzer, remove and disconnect the
collector cable from the sensor leaving it attached to the
electrometer board. (Consult schematic and assembly drawings
for circuitry and location). With this cable disconnected, the
electronic circuitry is completely isolated from the gas control
system and cell.
5.1.1 Anode Voltage Check
If the output can be adjusted by the zero control (the above section,
step 2), the cell anode voltage should be verified as follows:
WARNING: THESE PROCEDURES SHOULD BE CARIED OUT
ONLY BY PERSONNEL FAMILIAR WITH HIGH
VOLTAGE CIRCUIT BOARDS. THE ANODE-IGNITER
UNIT AND ASSOCIATE CIRCUITRY INVOLVE
DANGEROUSLY HIGH VOLTAGES.
Refer to the cell wiring diagram. Using a voltmeter set to measure
125 VDC, check the voltage on either of the anode-igniter electrodes, as
follows:
1. Connect the negative voltmeter lead to ground and the positive
lead to either electrode. Be careful not to short the circuit by
touching both an electrode and the cell body simultaneously. The
reading obtained should be 125±10 VDC.