Teledyne 335 - Analog control room monitor for personnel safety - Manual (Page 12)

TELEDYNE ANALYTICAL INSTRUMENTS
2 Operational Theory Model 335
2-6
LED’s; they also enable the oscillator of the audible (beeper) alarm. The
alarm relays themselves are ultra-sensitive and require only a few
milliamps driving current. Jumpers A through H and J through R allow the
alarms to be connected in either LOW or HIGH configuration. The refer-
ence voltage for the alarm comparators is taken from the reference com-
parator circuit (which also monitors the battery and AC line voltage lev-
els.)
Comparator sections A2c and A2d compare the battery voltage and a
voltage corresponding to the AC line voltage with a 1V reference level
produced by A1b from D7 and P3. To represent the line voltage, the
secondary of the power transformer and a voltage divider are used. If
either the battery voltage or the AC line voltage drop below relative preset
levels, the appropriate LED will light. Low voltage LED signals must be
acknowledged and the problem corrected as soon as possible; eventually,
the battery voltage will weaken to the point that the LED’s cease to warn
of the problem.
The 1V reference is also applied to the two alarm setpoint networks
consisting of P4/P19 (CAUTION SET) and R20/P5/R21 (DANGER SET),
which supply the reference voltages for the two alarm comparators. The
positions of the sliders of setpoint potentiometers P4 and P5 determine the
reference levels of the two comparators, and consequently provide the
setpoints of the two alarms.
2.4 Alarms
When the alarm setpoints are properly adjusted, they provide an
operational band that covers all acceptable oxygen concentrations. If the
oxygen level at the sensor crosses the adjusted setpoint of one of the
alarms, that alarm will cause the switching of relay contacts. Normally
open (N.O.) and normally closed (N.C.) circuit connections at the intercon-
nection terminal strip will be reversed. Thus, a circuit that is open (turned
off) in a non-alarm condition will be closed (turned on) when its alarm is
activated, and vice-versa.
As per OSHA specifications, the standard factory setting of the two
alarms provides a “CAUTION” alarm at 20% oxygen (at the sensor) and a
“DANGER” alarm at 19.5% oxygen. To cover special cases, a limited
amount of adjustment is possible.