Constant-Pressure Control; Description; Function - Grundfos CU 301 Installation And Operating Instructions Manual

1. Constant-pressure control

The control unit CU 301 is for use only with Grundfos
SQE pumps incorporating electronic power factor
correction (PFC).

1.1 Description

The system maintains a constant pressure within the
maximum pump performance in spite of a varying
water consumption.
The CU 301 is designed for wall mounting only.
1
4
Example of a system with constant-
Fig. 1
pressure control
Pos. Description
1 CU 301
2 Diaphragm tank (2 gal.)
3 Pressure sensor
4 SQE pump

1.2 Function

The pressure is registered by means of the pressure
sensor, which transmits a 4-20 mA signal to the
CU 301. The CU 301 adjusts the pump performance
accordingly to maintain constant pressure by chang-
ing the pump speed.
Mains borne signalling
The communication between the CU 301 and the
pump is via the power supply cable.
This communication principle is mains borne signal-
ling (or power line communication). Using this princi-
ple means that no additional cables to the pump are
required.
The communication of data is effected via a high-fre-
quency signal transmitted to the power supply cable
and led into the electronics unit by means of signal
coils incorporated in the motor and the CU 301
respectively.
In situations where multiple CU 301 pump power
cables are run parallel in wiring trays or conduit and
less than 10-12 inches apart, the possibility for
undesired communication between units exists.
When this occurs, intermittent or continuous
"No contact" is typically seen. Other unexpected
errors may also be seen.
Refer to section 5.3.10 for further instructions.
2
3
CU 301
CU 301
1
2
3
7
8
Principle of mains borne signalling
Fig. 2
Pos. Description
1 Supply to the electronics
2 Signal coils
3 Capacitor
Electronics for the control of
4
the communication
5 On/Off button
6 Sensor signal
7 Mains supply
8 Communication signals
5
4
R 100
6
5