7 Limit Switches
This Chapter describes the setting of the relay limit switches for continuous level
measurement. It is divided into two Sections:
• Relay settings
• Applications
Level measurement Silometer FMC 671 Z/676 Z transmitters have two independent relays, which switch
according to the size of the measured value at V0H0.
• Each limit switch can be operated in minimum or maximum fail-safe mode,
i.e. when the level drops below or exceeds the switch point the relay is
de-energized.
• The hysteresis of each limit switch is freely selectable.
• Relay 1 is normally assigned to channel 1 and relay 2 to channel 2, however,
the assignment can be changed.
The switch points are entered in the units selected during calibration and linearization,
i.e:
• No linearization: level units entered
• No linearization, calibration in volume units: volume units entered
• Linearization: volume units entered
The relays are controlled by the matrix fields V1H0 to V1H4 for relay 1 and V1H5 to V1H9
for relay 2. Table 7.1 summarizes their function.
Limit switching If the Silometer is used as a limit switch only, the relay switch point is fixed by the position
of the probe for Liquiphant or Soliphant and at V8H6 for capacitance probes. The
hysteresis is set as a switching time delay at V8H3, see Chapter 8, Sections 8.2 and 8.3.
By entering »2« in V1H4/V1H9, both relays can be assignet to channel 2, the safety mode
can be set in V1H1 and V1H5. The default setting = 0, relays de-energise, is taken for
the relay at fault.
Note!
• If operating mode 1 or 2 is selected and both relays are assigned to channel 2,
switch point and hysteresis must be entered in Hz.
Matrix
Relay 1
Matrix
Relay 2
Significance Default
V1H0 V1H5 Relay switch point 90.0
V1H1 V1H6 Fail-safe mode
0 = Minimum:
relay de-energises when level < switch point
1 = Maximum:
relay de-energises when level > switch point
At fault
relay reacts according to V1H3/V1H8 setting
1
V1H2 V1H7 Relay hysteresis 2.0/0.1
V1H3 V1H8 Relay at fault
0 = de-energises
1 = follows analogue output 1/2 according to
setting at V0H7
0
V1H4 V1H9 Relay assignment
1 = Channel 1
2 = Channel 2
1/2
Table 7.1:
Relay control parameters
Silometer FMC 671 Z/676 Z Chapter 7: Limit Switches
36
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