Regulated Differential Power Supply Printed Circuit Board - Teledyne 402R-EU Instruction Manual

Chapter 5
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 250
volts. Output tolerance is ±22 volts from the specified 250 volts, due to
variation in components from unit to unit.
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 is turned on by the relay to alarm person-
nel that a flame-out condition has occurred.
The controlling thermistor is located within the upper section of the
sensor cell assembly. The electronic circuit components are mounted on
the same printed circuit board as the anode power supply. The relay is
located on the motherboard and the indicator light on the control panel.
The thermistor is located in the circuit so that it controls the bias on
the switching transistor. The circuit is factory set so that with the flame
burning, the bias on the transistor is such that it conducts and holds the K3
relay energized. When energized, the relay extinguishes the Flame Out
indicator light. Conversely, if the flame goes out, bias to the switching
transistor is lost, the relay drops out, and the Flame Out light receives
power through normally closed contacts.
During ignition, the flame heats the thermistor, holding the relay in
the energized condition and the indicator light off. If the Flame Out light
comes on as the switch returns from its momentary IGNITE position, then
the flame is not burning, and the ignition procedure must be repeated.
Millivolt Output Resistors:
are selected per application. They are used to convert the voltage signal
obtained from the wiper of the span potentiometer into an auxiliary milli-
volt output.
5.5.2 Regulated Differential Power Supply Printed
Schematic No.
Assembly Dwg. No. A-9306
The purpose of this power supply circuit is to provide the DC voltage
requirements of the various electronic circuits within the analyzer or
system. An input voltage of 40-50 VAC at card pins 8 and 10 (center-
tapped to ground at pin 14) is converted to a non-regulated +24 VDC at pin
5-12
Resistors R5 and R6 on this PC board
Circuit Board
B-33129
Teledyne Analytical Instruments
Model 402
R-EU