Siemens LMU64 Series - Sensor input “Pressureless header”

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Siemens Building Technologies Basic Documentation LMU54... / LMU64... CC1P7494en
HVAC Products 6 Clip-in function module AGU2.51x 07.11.2002
In this case, the relative boiler output is predefined via an analog signal.
This analog signal can be a current signal (0...20 mA, 4...20 mA) or a voltage signal (DC
0...10 V).
The analog signal is transmitted to the LMU… and applied to the possible output range
as a percentage value.
The threshold from which the analog signal shall activate the predefined load is defined
with the help of parameter «PanfoExtSchwelle». This parameter also defines the
minimum value of the analog signal.
The range of the analog signal between threshold and maximum value is converted into
an output signal in the range 0...100 %.
If the analog signal is near the parameterized threshold, the boiler will be operated at
the minimum relative output. In the case of maximum value of the analog signal, control
takes place with the maximum relative boiler output.
If the analog signal lies below the parameterized threshold, the predefined output will not
be active.
U (V)
10
8
6
4
2
0
0
Parameter «PAnfoExtSchwelle» (%)
I (mA)
20
16
12
7494d43E/0702
100 (% rel. Boiler output)
8
4
0
Predefined output
This function facilitates control of the boiler to the flow temperature after the
pressureless header. For that purpose, a sensor located in the flow after the
pressureless header must be connected to the input of the clip-in function module.
The function is based on the following conditions:
− In addition to heating circuit 1, the hydraulic diagram contains no other heating circuits
− An operational boiler return sensor
In pure heating mode (that is, when DHW heating is not active), the boiler temperature
is controlled to the value of this sensor. This means that the boiler is heated up until the
flow temperature after the pressureless header has reached the required level.
If no boiler return sensor is connected, an error code will be delivered.
If the state of the boiler return sensor changes from “Present” to “Faulty”, the actual
boiler temperature will be maintained again and an error code delivered. ...
Predefined output
Sensor input
“Pressureless header”