VLT
®
8000 AQUA
■ Example of application - Constant pressure
regulation in water supply system
The demand for water from waterworks varies considerably during the course of a day. In the night,
practically no water is used, while in the morning and in the evening the consumption is high. In order to
maintain a suitable pressure in the water supply lines in relation to the current demand, the water supply
pumps are equipped with speed control. The use of a frequency converter enables the energy consumed by
the pumps to be kept at a minimum, while optimizing the water supply to consumers.
A VLT 8000 AQUA with its integral PID controller ensures simple and quick installation. For example, an
IP54/NEMA 12 unit can be mounted close to the pump on the wall and the existing mains cables can be
used as mains supply to the frequency converter. A Pressure transmitter (e.g. Danfoss MBS 33 or MBS
3000) can be fitted a few meters (feet) from the joint outlet point from the waterworks to obtain closed loop
regulation. Danfoss MBS 33 and MBS 3000 is a two-wire transmitter (4-20 mA) that can be powered directly
from a VLT 8000 AQUA. The required setpoint (e.g. 5 bar) can be set locally in parameter 418 Setpoint 1.
Assume:
Transmitter is scaled 0-10 Bar, minimum flow
is achieved at 30 Hz. An increase in motor
speed increases the pressure.
Set the following parameters:
Par. 100 Configuration Closed loop [1]
Par. 201 Minimum Output Frequency 30 Hz
Par. 202 Maximum Output Frequency 50 Hz (or 60 Hz)
Par. 204 Minimum Reference 0 Bar
Par. 205 Maximum Reference 10 Bar
Par. 302 Terminal 18 Digital inputs Start [1]
Par. 314 Terminal 60, analog input current Feedback signal [2]
Par. 315 Terminal 60, min. scaling 4 mA
Par. 316 Terminal 60, max. scaling 20 mA
Par. 403 Sleep mode timer 10 sec.
Par. 404 Sleep frequency 35 Hz
Par. 405 Wake-up frequency 45 Hz
Par. 406 Boost setpoint 125%
Par. 413 Minimum Feedback 0 Bar
Par. 414 Maximum Feedback 10 Bar
Par. 415 Process units Bar [16]
Par. 418 Setpoint 1 5 bar
Par. 420 PID control action Normal
Par. 423 PID Proportional gain 0.3*
Par. 424 PID Integral time 30 sec.*
* The PID tuning parameters depend on the actual system dynamics.
MG.83.A2.02 - VLT is a registered Danfoss trademark
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