Two-point operation
with two relays
This mode of operation is achieved by setting the hysteresis of both relays such that:
• minimum level/volume + hysteresis = maximum level/volume
• maximum level/volume – hysteresis = minimum level/volume
Relay 1 is set for maximum and relay 2 for minimum fail-safe mode in the same channel:
• When the level drops below the minimum relay 2 de-energises, relay 1
energises
• When the level rises above the maximum relay 1 de-energises, relay 2
energises.
Step Matrix Entry Significance
1 V1H9 1 Assign relay 2 to channel 1
2 - »E« Register entry
3 V1H0 e.g. 1800 Switch point, relay 1 = 1800
4 - »E« Register entry
5 V1H1 1 Maximum fail-safe mode
6 - »E« Register entry
7 V1H2 e.g. 1600 Hysteresis = 1600, the relay energises again at 200
8 - »E« Register entry
9 V1H5 e.g. 200 Switch point, relay 2 = 200
10 - »E« Register entry
11 V1H6 0 Minimum fail-safe mode
12 - »E« Registers entry
13 V1H7 e.g. 1600 Hysteresis = 1600, the relay energises again at 1800
14 - »E« Register entry
Switch point 1
e.g. 1800
Hysteresis
e.g. 1600
Switch point 2
e.g. 200
Relay 1
Maximum fail-safe
energised de-energised energised
Relay 2
Minimum fail-safe
de-energised de-energised
Relay 1 =
Maximum fail-safe
Relay 2 =
Minimum fail safe
BA053E38
z22 d24 z24 z22 d24 z24 z22 d24 z24
energised
z18 d20 z20 z18 d20 z20 z18 d20 z20
Fig. 7.3:
Two-point operation
with two relays
Silometer FMC 671 Z/676 Z Chapter 7: Limit Switches
40
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