Chapter 5 55
Operation
• Restart the ignitor by turning on the power supply to the PFPD. (If
WinPulse has already been activated and the power supply is still on, the
ignitor can also be restarted by setting the Ignitor Current to 3.3 A in the
Board/Channel Parameters screen.) Reset the ignitor current to 2.8 A once
a regular pulse has been obtained.
11. If the PFPD still does not pulse or continues to pulse erratically, the gas flows
may have to be readjusted. If the settings of the column carrier gas or the H
2
gas flow are set too high relative to the air flow, ignition may be difficult due
to excessive cooling of the ignitor coils. It may, therefore, be necessary to
reduce the column gas or H
2
flow rates, or alternatively to increase the Air 2
gas flow slightly.
12. To change the default PFPD settings, go to the Parameters menu and select
Gates/Modes or Board/Channel. If the toolbar is active, the Gates/Modes
option can also be selected by clicking on the
button in the toolbar, while
the Board/Channel option can be selected by clicking on the
button.
13. Observe the chemiluminescence emission signal displayed in the Main Screen
of the WinPulse software program (see Figure 3.1). If only one peak is
observed, the flame may not be propagating fully in the combustor. The fine
adjust needle valve may have to be turned counterclockwise to increase the
H
2
/Air 1 mixture flowing through the combustor. The flow rate of Air 2 may
also have to be reduced to decrease the flow rate of the wall gas mixture
relative to the combustor gas mixture.
14. Slowly turn the fine adjust needle valve clockwise (to reduce the flow of the
H
2
/Air 1 flow into the combustor) until the PFPD goes into the tick-tock mode
(see “Principle of Operation” in Chapter 1). At the point that the PFPD goes
into the tick-tock mode , turn the fine adjust needle valve counterclockwise
until the PFPD goes out of tick-tock mode. Then turn the valve one-half turn
counterclockwise for stable PFPD operation.
15. Verify that the PMT voltage is set to the appropriate level.
• Go to the Board/Channel Parameter screen and set the PMT Voltage to
450 and the Range to 10 or 1.
• While monitoring the chromatography baseline, gradually increase the
PMT voltage. Initially, only the baseline will rise but the noise will not
change. Above a certain PMT voltage, the noise will start to increase.
When the noise is twice its value at the initial low PMT voltage setting,
the voltage is the optimal PMT voltage. A higher than optimal PMT
voltage will reduce the dynamic range; a lower PMT voltage may reduce
the PFPD sensitivity.
Note: If an oscilloscope is used when starting up the PFPD, the following steps
should be followed.
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