Teledyne 4020 - Hydrocarbon analyzer - Manual (Page 27)

Total Hydrocarbon Analyzer Operational Theory
Teledyne Analytical Instruments 11
an input impedance measuring in the billions of ohms. It is static
sensitive and highly susceptible to contamination. Special care must be
taken in handling this PC board.
Refer to Section 5.5.4: Electrometer-Amplifier PC Board for more
information concerning the electrometer-amplifier and the other printed
circuits that follow.
2.3.2 Anode Power Supply
The high voltage anode power supply components are mounted on
the anode power supply printed circuit board. High voltage regulation is
achieved through the use of series-connected zener diodes. The
simplicity of this circuit’s design can be attributed to the extremely low
current demand of the anode circuit. The positive output voltage is
nominally 125 volts. Output tolerance is ±10 volts from the specified
125 volts.
2.3.3 Flame Guard Circuit
A thermistor-controlled, transistorized switching circuit is employed
to operate a relay in the event of a flame-out condition. A panel indicator
light and fuel shut-off solenoid valve are operated by the relay to alarm
personnel that a flame-out condition has occurred. The fuel shut-off
solenoid valve stops the hydrogen flow.
2.3.4 Flame Ignition Circuit
The flame ignition circuit includes the anode-igniter electrode (in the
detector cell), a transformer, and processor controlled relay. The circuit
is automatically energized after the warm up count down timer expires.
If automatic ignition fails, there will be a message that reports this,
and the flame can be manually ignited by pressing simultaneously the
Up and Down key.
2.3.5 Proportional Temperature Control Circuit
The temperature of the isothermal chamber containing the sampling
components is regulated by a thermistor-directed electronic circuit. The
thermistor and heating element are located in the chamber, and the
balance of the circuit components are mounted on the temperature
controller printed circuit board. A temperature limit switch protects the