Emerson Rosemount 2120, Справочное руководство

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5 Operation
5.1 Output mode and time delay
All electronics cassettes have a rotating switch for setting the output to be "Dry On" (on
when the fork is sufficiently dry) or "Wet On" (on when the fork is sufficiently wet).
The electronics uses hysteresis to help prevent constant switching of the output from dry-
to-wet and wet-to-dry states due to splashing or intermediate conditions. To further
prevent false switching, the rotating switch also sets a time delay of up to 30 seconds
before the output changes.
A small cut-out in the rotating switch indicates the present mode and time delay.
Figure 5-1: Top-down View: Example Cassette Inside Housing
OPERATION MODE
Dry On Mode
Dry
Wet
Wet On Mode
Dry
Wet
Dry On Wet On
Seconds Delay
0.3 0.3
3
30
10
1
3
30
10
1
1 2 3
OUT
+
-
4
PLC/PNP
Isolate Supply
Before Removing
A B
A. 'Heartbeat' LED
B. Rotating switch for setting output mode and time delay
The recommended mode for high level alarm installations is the "Dry On" mode ( Figure
5-2 ).
Figure 5-2: Typical Settings for High Level Applications
Dry On Wet On
Seconds Delay
0.3 0.3
3
30
10
1
3
30
10
1
A
A. Mode “Dry On” and 1 second time delay
The "Wet On" mode is recommended for low level alarm installations ( Figure 5-3 ).
Reference Manual Operation
00809-0100-4030 March 2022
Rosemount 2120 Level Switch 53