Comparator Alarm Printed Circuit Board - Teledyne 402R-EU Instruction Manual

Total Hydrocarbon Analyzer
The comparator alarm circuit consists simply of an operational ampli-
fier used to turn a transistor on or off according to logic wiring, in response
to an increasing process signal. The transistor, in turn, in its "turned on"
state, activates a contact relay to provide switching contacts accessible at
the interconnection terminal strip.
For the number 1 alarm circuit, potentiometer P3 sets a reference
voltage at strapping point B on the circuit board. The process signal is
present at strapping point A. Depending upon the strapping configuration
(jumper placement), IC A1 can be used in its inverting or non-inverting
mode to control relay K1 by means of NPN transistor Q2.
When in its inverting mode (jumpers JP3 and JP4 installed), A1
receives the positive signal voltage at its inverting input (pin 2) and the
positive reference voltage at its non-inverting input (pin 3). When the
voltage at pin 2 is more positive than that at pin 3, A1's output goes low
(negative), and the transistor is turned off, de-energizing relay K1. Thus,
K1 is energized when the signal is below the point set by P3 (Alarm
setpoint 1) and de-energized above the setpoint.
In its non-inverting mode (jumpers JP1 and JP2 installed), A1
switches to a negative output when the signal voltage (now applied to pin
3) is less than the reference voltage (pin 2), to a positive output if the
signal output is greater, and vice versa. Once again, when A1's output is
positive, Q2 is turned on, energizing K1; negative A1 output turns off Q2,
de-energizing K1. Thus configured, the alarm relay is energized "above
setpoint", or when the signal is greater than the reference.
For number 2 alarm circuits, setpoint potentiometer P4 is used to
adjust alarm setpoint #2. IC A2, transistor (PNP) Q4, and alarm relay K2
are added to make up the second alarm. Transistor Q4 (PNP) acts in the
reverse manner from Q2 (NPN), turning on with a negative A2 output, off
with positive. Installing jumpers JP7 and JP8 configures the second alarm
to energize below alarm 2 setpoint (P4), and installed jumpers JP5 and JP6
causes the alarm to energize above setpoint.

5.5.5 Comparator Alarm Printed Circuit Board

Schematic No.
Assembly Dwg. No. A-9309 (dual)
Teledyne Analytical Instruments
Maintenance and Troubleshooting
B-33128
5-17