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Instruction Manual
245364-V
May 2002
3-12 Operation Rosemount Analytical Inc. A Division of Emerson Process Management
Model 755A
3-6 DUAL ALARM OPTION
a. Initial Calibration and Selection of
Setpoints for Alarms
The ALARM 1 and ALARM 2 circuits have
independent setpoint and deadband
adjustments (see Table 3-1, page 3-5,
and Figure 3-2, page 3-7). Initially the
ALARM 1 and ALARM 2 setpoint
adjustments must be calibrated by means
of the ALARM 1 and ALARM 2 calibration
adjustments.
1. Set TEST switch to NORM.
2. Pass upscale standard gas through
the analyzer at a flow rate of 50 to
500 cc/min.
3. Verify that ALARM 1 and ALARM 2
deadband adjustments are fully
counterclockwise to set deadband at
minimum. Normally these
potentiometers are factory-set for
minimum deadband. Both
potentiometers must remain at this
setting throughout calibration of the
alarm setpoints.
Calibration of ALARM 1, HIGH:
Rotate setpoint adjustment R64 full
counterclockwise.
Adjust SPAN control to obtain a display or
recorder reading exactly fullscale. If the
fullscale setting cannot be reached, then
set to a reading higher than the desired
alarm setpoint.
Set ALARM 1 calibration adjustment,
R63, to its clockwise limit. Turn R63
counterclockwise the minimum required to
energize ALARM 1 (relay K1, Figure 3-4,
page 3-13). Energization may be verified
by connecting an ohmmeter to relay
terminals on 638254 Alarm Relay
Assembly (Figure 2-1, page 2-2).
Calibration of ALARM 2, LOW:
1. Rotate setpoint potentiometer R67 full
counterclockwise.
2. Adjust SPAN control to obtain a display
or recorder reading exactly fullscale. . If
the fullscale setting cannot be reached,
then set to a reading higher than the
desired alarm setpoint.
3. Set ALARM 1 calibration adjustment,
R67, to its clockwise limit. Turn R63
counterclockwise the minimum required
to energize ALARM 1 (relay K1, Figure
3-4, page 3-13). Energization may be
verified by connecting an ohmmeter to
relay terminals on 638254 Alarm Relay
Assembly (Figure 2-1, page 2-2).
Setpoint of ALARM 1, HIGH
1. With span gas flowing, adjust SPAN
Control to read desired alarm setpoint
on display or recorder.
2. Turn setpoint adjustment, R64,
clockwise to energy relay.
3. Check this setting by adjusting the
SPAN Control to lower the output
below the setpoint. This will re-
energize the relay. Turning R64
above the setpoint will energize the
relay.
Setpoint of ALARM 2, LOW
1. With span gas flowing, adjust SPAN
Control to read desired alarm setpoint
on display or recorder.
2. Turn setpoint adjustment, R68,
clockwise to energy relay.
3. Check this setting by adjusting the
SPAN Control to lower the output
below the setpoint. This will re-
energize the relay. Turning R68
above the setpoint will energize the
relay.