TELEDYNE API T703U - Photometer Pneumatic Operation; Photometer Layout - Top Cover Removed

Principles of Operation Teledyne API T703/T703U Calibrator Operation Manual
206
 A thermistor and DC heater attached to the UV Lamp to maintain the Lamp
at an optimum operating temperature.
 42 cm long quartz absorption tube.
 A thermistor attached to the quartz tube for measuring sample gas
temperature.
 Gas inlet and outlet mounting blocks that rout sample gas into and out of the
photometer.
 The vacuum diode, UV detector that converts UV light to a DC current.
 A preamplifier assembly, which convert the Detector‟s current output into a
DC Voltage then amplifies it to a level readable by the A to D converter
circuitry of the instrument‟s motherboard
Absorption Tube
UV Lamp Heater
Control PCA
Sample Gas
Outlet
UV Lamp Power
Transformer
Power Connector
from
+15 VDC power supply
UV Lamp Power
Supply
(200 VAC @ 30 kHz)
Sample Gas Inlet
UV Detector
Preamp PCA
UV Detector
Sample Gas
Thermistor
UV Lamp
UV Lamp Thermistor
(UV Lamp Heater Behind Thermistor)
Figure 9-23: O
3
Photometer Layout – Top Cover Removed
PHOTOMETER PNEUMATIC OPERATION 9.6.3.
The flow of gas through the photometer is created by a small internal pump that
pulls air though the instrument. There are several advantages to this “pull
through” configuration. Placing the pump down stream from the absorption tube
avoids problems caused by the pumping process heating and compressing the
sample.
In order to measure accurately the presences of low concentrations of O
3
in the
sample air it is necessary to establish and maintain a relatively constant and stable
volumetric flow of sample gas through the photometer. The simplest way to
accomplish this is by placing a flow control assembly containing a critical flow
orifice directly upstream of the pump but down stream from the absorption tube.
The critical flow orifice installed in the pump supply line is tuned to create a gas
flow of 800 cm
3
/min. A pressure sensor and a flow sensor, located on the O
3
generator / photometer pressure flow sensor PCA, monitor the pressure and flow
rate of the gas passing through the photometers absorption tube.
See Figure 9-18 through Figure 9-22 for depictions of the gas flow related to the
photometer.
07223D DCN7107