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Liquidew EExd User's Manual
AL1
NC C
NO NC C
1 2 3 4 5 6
2.5.3
Analog and Digital Communications
Two active 4-20 mA outputs and a Modbus RS485 digital interface (see Appendix F for
details) are provided with the Liquidew EExd. mA1 and mA3 output the moisture or
dew-point values. mA2 and mA4 output the sample temperature values of Channels 1
& 2 respectively.
NOTE: The maximum output resistance for the 4-20 mA outputs is 500Ω.
See Section 3.7 on the setting of the 4-20 mA outputs via the user interface and
Appendix F on setting the outputs via the Modbus interface.
Refer to Figure 7 for cable wiring.
2.5.4
Process Alarms and Analyzer Status Alarms
Each channel has an associated process and fault alarm, as shown below:
AL1: Channel 1 process alarm
AL2: Channel 1 analyzer status alarm
AL3: Channel 2 process alarm (Optional)
AL4: Channel 2 analyzer status alarm (Optional)
The process alarm contacts can be set as either Normally Closed (
N/O
Open (
).
The process alarm contacts change from
greater than the alarm set point.
The fault alarm contacts change from
channel occurs or when there is a supply failure.
Michell Instruments
AL2
AL3
AL4
NO
NC C
NO NC C
NO
7 8 9 10 11 12
PL16
PL20
Enclosure wall
Figure 6
COMMS
Channel 1
B
A
GND
16 17 18 19
13 14 15
PL15
L
E N
Hook-up Wiring Diagram
N/C
N/O
to
when the moisture value becomes
N/C
to
N/O
when an error associated with the
INSTALLATION
Optional
Channel 2
20 21 22 23
PL14
PL19
Gland
Cable screen
N/C
) or Normally
13
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