Filter
Top Products
TELEDYNE INSTRUMENTS
Theory of Operation 460L Instruction Manual
60 05228 Rev B
PRINTED DOCUMENTS ARE UNCONTROLLED DCN 5164
Gas Pressure Sensor: This absolute pressure sensor measures the gas pressure in the
measurement cell upstream of the Pump. The sample pressure is used by the CPU to
calculate O
3
Concentration (see Formula 10-3 in Section 10.1). This sensor outputs an
analog signal to the sensor microprocessor.
Measure / Reference Valve: This valve alternates the O
3
gas stream between a direct
path to the absorption tube and a path that first passes it the O
3
scrubber. The state of this
valve is the Sensor Module PCA (see Section 10.3.2.2).
10.3.2.2. Sensor Module PCA
The sensor module PCA performs the real work of operating the O
3
sensor module. It gathers the
various measurements used to calculate the O
3
concentration and performs all basic computations
related to determining the O
3
concentration of the source gas.
It includes:
Sensor Signal A/D Conversion: The output of the monitor’s O
3
sensor and the pressure
sensor are converted into digital signals that the CPU can understand by two analog to
digital converters (A/D) located on the sensor PCA.
LOW RESOLUTION A/D
: A 12-bit, SAR converter that digitizes the output of the
monitors pressure sensor.
HIGH RESOLUTION A/D
: This component digitizes the signal output by the UV detector
of the monitor’s measurement detector. Since the reference detector output requires a
large dynamic range and superior noise rejection, a Delta-Sigma type A/D Converter is
used here.
Sensor Microprocessor: This IC provides two important functions.
A/D Converter Signal Selection
: The A/D converter can only convert one signal at a time.
The sensor microprocessor selects which of the sensor inputs is to be converted(pressure
sensor or measurement detector), starts the conversion process, stops it and extracts the
digital data.
Data Output
: The sensor microprocessor collects data from the various digital sensors as
well as the data converted by its internal A/D and sends it to the main CPU via an internal
RS-485 serial data bus.
UV Lamp Heater Control
: The sensor microprocessor also provides direct control of the UV
lamp heater by turning it on and off via a transistor using high frequency pulse width
modulation. The output of the UV Lamp sensor is converted by the micrprocessor’s A/D
converter. Based on this digital value the sensor microprocessor sends out pulses that
turn the heater ON/OFF. The more heat needed the longer the width of the ON (logic high)
pulse and the shorter the width of the OFF (logic low) portion of the pulse.
Measure / Reference Valve Control: The Measure/Reference valve is actuated by a 12
VDC solenoid valve driver that is controlled by timing circuitry built into the sensor module
board.