Flow Switch / Water Pressure Supervision; Function Of Flow Switch; Function Of Pressure Switch; Pressure Sensor - Siemens LMU54 Series Basic Documentation

Flow switch / water
pressure supervision

Function of flow switch

Function of pressure switch

Pressure sensor

Note
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Input «Heating circuit monitor» permits the use of a flow switch or of water pressure
supervision through connection of the relevant switch. The following functions can be
parameterized:
KonfigRg5.1 KonfigRg5.0
0 0
0 1
1 0
1 1
With this function, the switch closes when adequate amounts of water pass through the
boiler's heat exchanger. Hence, the heating circuit flow switch may be evaluated only if,
in the case of demand for heat, water passes through the primary heat exchanger.
In the case of DHW heating, the heating circuit flow switch will not be evaluated with the
following systems:
System 4
36
52
68
The heating circuit flow switch test is always started when demand for heat is triggered
(internally or externally).
When the switch is closed, startup can immediately be initiated. When open, the LMU...
will lock startup after a waiting time of 12 seconds. Then, a change to start prevention or
lockout with the relevant diagnosis is made (status or error code).
If the switch closes after that period of time and start prevention was triggered, it will be
canceled again and delivery of the status code is suppressed.
If there is no demand for heat, there will be no evaluation of the heating circuit flow
switch during pump overrun or during a kick function.
In that case, input «Heating circuit monitor» watches the water pressure (water shortage
switch).
A closed pressure switch immediately enables the startup commands to the burner
control and control of the pumps. If the pressure switch is open, start prevention or
lockout will only be triggered after 12 seconds.
To ensure protection against water shortage, pump control will also be locked.
For the diagnosis, a status or error code is generated in that case.
If the water pressure rises again and there is start prevention, it will automatically be
canceled again and pump control enabled.
Plausibility check of pressure sensor:
If a configuration with water pressure sensor was selected (KonfigRg3) and water
pressure supervision was released (KonfigRg5), the LMU... must read in a valid value
for the water pressure.
Otherwise, there will be either start prevention with error code or the unit will initiate
lockout (KonfigRg5). In any case, the pump will be deactivated to prevent dry run.
Only one of the 3 devices (flow switch, pressure switch or pressure sensor) can be used
for supervision. Combinations are not possible.
Basic Documentation LMU54... / LMU64...
3 Functions
Impact
Flow switch triggering lockout
Flow switch triggering start prevention
Pressure switch triggering lockout
Pressure switch triggering start prevention
CC1P7494en
07.11.2002