Thermo Scientific FTIR, Руководство пользователя

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Figure 4-5: To set the pressure and flow
1. Open the FTIR INLET RESTRICT and FTIR OUTLET RESTRICT needle valves completely.
Adjust the knob on the flowmeter labelled “FTIR FLOW TO VENT” to be wide open.
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If your system includes the optional eductor panel.
a. On the eductor panel on the rear of the MGS rack, turn on the source of compressed air
used by the eductor system to create a vacuum.
b. Turn the regulator dial on the Pressure Gauge to adjust the compressed air pressure to a
minimum of 500 kPa, or 70 psia.
c. On the HVD front panel, use the SAMPLE PUMP ON/OFF switch to turn on the power to
the Eductor vacuum source.
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If using a standard vacuum pump, on the font panel of the HVD, use the Sample Pump On/Off
switch to turn on the power to the vacuum.
2. Check the pressure value on the Alicat LCD. If the pressure reading is higher than 650 mmHg, it
means the total gas flow is higher than the Alicat can control with the given vacuum and flow
rates. Adjust the FTIR INLET RESTRICT valve to restrict the flow slightly. With the input flow
reduced to a similar volume as the vacuum pump can handle, the Alicat gauge will compensate
and maintain the pressure at the set point (650 mmHg default).
Note There is some delay before the gas cell pressure stabilizes. The length of the delay
varies depending on gas cell volume, the length of sample line, and the vacuum/flow rate
values.
3. Check the flow rate in liters per minute through the FTIR FLOW TO VENT flowmeter. If the flow is
too high for the desired rate, adjust the flowmeter knob to reduce the flow.
Note You may need to adjust the FTIR INLET RESTRICT Swagelok valve again to
compensate for the change in flow rate and keep the Alicat value constant.
Note The Alicat pressure control circuit uses some of the gas flow for valve control.
Consequently, even when the FTIR FLOW TO VENT flowmeter is closed completely to the
sample gas, you will still see a small flow continuing through the flowmeter.
While the sample source is typically at atmospheric pressure, your nitrogen or span gas is often
pressurized, to “push” the gas through the cell. If so, you may have to use the CALIBRATION FLOW
flowmeter to reduce the gas flow through the system in able to maintain the set pressure value.
Thermo Scientific Modular Gas System User Guide 47
Operation