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Teledyne API T703/T703U Calibrator Operation Manual Principles of Operation
217
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.
9.6.4. PHOTOMETER ELECTRONIC OPERATION
Photometer
Photometer
Lamp Heater
Motherboard
Photometer
Lamp Power
Supply
Sensor Inputs
P
C
1
0
4
B
u
s
I
2
C Bus
Photometer
Pump
Thermistor Interface
Photometer
Detector
Preamp
A/D
Converter
RELAY PCA
I
2
C
Status
LED
y
PC 104
CPU Card
Disk on
Module
Absorption tube
Photometer
Detector
Photometer
Sample Gas
Pressure
Sensor
Photometer
UV Lamp
Temperature
Photometer
Sample Gas
Temperature
Photometer M/R
Valve
(Located on O
3
Generator Assembly)
Figure 9-24: O
3
Photometer Electronic Block Diagram
Like the O
3
generator, the O
3
photometer and its subcomponents act as peripheral
devices operated by the CPU via the motherboard. Communications to and from the
CPU are handled by the motherboard.
Outgoing commands for the various devices such as the photometer pump, the UV lamp
power supply the U\V Lamp heater are issued via the I
2
C bus to circuitry on the relay
PCA which turns them ON/OFF. The CPU also issues commands over the I
2
C bus that
cause the relay PCA to cycle the measure/reference valve back and forth.
Incoming date the UV light detector is amplified locally then converted to digital
information by the motherboard. Output from the photometers temperature sensors is
also amplified and converted to digital data by the motherboard. The O
3
concentration
of the sample gas is computed by the CPU using this data (along with gas pressure and
flow data received from the pressure sensors.
07223C DCN6572