Rosemount 755, Instruction Manual

Page: 29 / 94

I
NSTALLATION
748183-H
2-7
Rosemount Analytical
November 1997
When input signal moves upscale through this point, the coil of
ALARM 1 relay (K1) is energized, providing continuity between the
common and normally-closed contacts of the relay.
ALARM 1 Setpoint
When input signal moves downscale through this point, the coil of
ALARM 1 relay (K1) is de-energized, providing continuity between the
common and normally-open contacts of the relay.
ALARM 2 Setpoint
When input signal moves upscale through this point, the coil of
ALARM 2 relay (K2) is de-energized, providing continuity between the
common and normally-open contacts of the relay.
When input signal moves upscale through this point, the coil of ALARM
2 relay (K2) is energized, providing continuity between the common
and normally-closed contacts of the relay.
A. Typical ALARM 1 Setting
B. Typical ALARM 2 Setting
INPUT SIGNAL
Percent of Fullscale
INPUT SIGNAL
Percent of Fullscale
40
30
20
55
50
45
DEADBAND SET FOR
20% OF FULLSCALE
DEADBAND SET FOR
10% OF FULLSCALE
Removal of AC power from the analyzer, as in power failure, de-energizes both relays,
placing them in alarm condition. Switching characteristics of the Alarm 1 and Alarm 2
relays are as follows:
A
LARM
1 R
ELAY
The Alarm I relay coil is de-energized when the meter needle moves downscale
through the value that corresponds to setpoint minus dead-band. This relay coil is
energized when the needle moves upscale through the value that corresponds to
setpoint plus dead-band. See Figure 2-5A.
A
LARM
2 R
ELAY
Relay The Alarm 2 relay coil is de-energized when the meter needle moves upscale
through the value that corresponds to the setpoint plus dead-band. This relay coil is
energized when needle moves downscale through the value that corresponds to
setpoint minus dead-band, see Figure 2-5B.
F
IGURE
2-5. T
YPICAL
A
LARM
S
ETTINGS
A
LARM
R
ESET
Normally both the ALARM 1 and ALARM 2 functions incorporate automatic rest. When
the meter reading goes beyond the selected limits, the corresponding relay is de-
energized; when the meter reading returns within the acceptable range, the relay is
turned on.
If desired the ALARM 1 or ALARM 2 alarm function may be converted to manual reset.
The conversion consists of substituting an external push-button or other momentary-
contact switch for the jumper that normally connects the RESET terminals on the
Alarm Relay Assembly, see Figure 2-1. If the corresponding relay is now de-
energized, i.e., in alarm condition, the relay remains de-energized until the operator
momentarily closes the switch.