Grundfos LC 221, Инструкция по установке и эксплуатации, Страница: 9 / 796

English (GB)
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5.1.6 Level sensor, Multilift MD, MLD
The piezoresistive pressure sensor placed in the controller is
connected via a hose to a pressure tube in the tank. The screw
cap where the hose is connected includes a condensate trap and
a connection for a DN 100 tube. This tube, the pressure tube,
extends down into the tank. The rising liquid level compresses the
air inside the pressure tube and hose, and the piezoresistive
sensor transforms the changing pressure into an analogue signal.
The control box uses the analogue signal to start and stop the
pump and to indicate high water-level alarm. The pressure tube is
fixed underneath the screw cap and can be taken out for
maintenance, service and for cleaning the inside of the tube.
An O-ring ensures tightness.
The hose is supplied in lengths of 4 or 10 m. The hose must be
connected to the controller.
Fig. 6 Screw cap with hose, DN 100 tube and condensate
trap
5.2 LC 221 controller
The LC 221 is a level controller specially designed for controlling
and monitoring the Grundfos lifting stations, Multilift MD and
MLD. The basis for the control is the signal received continuously
from the piezoresistive, analogue level sensor.
The level controller switches the MD and MLD Multilift pumps on
and off according to the liquid level measured by the level sensor.
When the first start level is reached, the first pump will start, and
when the liquid level has been lowered to the stop level, the pump
will be stopped by the controller. If the liquid level rises up to the
second start level, the second pump will also start, and when the
liquid level has been lowered to the stop level, the pumps will be
stopped by the controller.
Starts alternate between the two pumps.
In case of pump failure in one pump, the other pump will take
over (automatic pump changeover).
An alarm will be indicated in case of high water-level in the tank,
pump failure, etc.
Furthermore, the level controller has many more functions as
described below.
Fig. 7 LC 221 level controller for Multilift MD and MLD
The LC 221 controller has the following functions:
• on/off control of two wastewater pumps based on a continuous
signal from a piezoresistive level sensor with alternating
operation and automatic changeover in case of pump failure
• motor protection with motor-protective circuit breaker and/or
current measurement as well as connection of thermal
switches
• motor protection via operating-time limitation with subsequent
emergency operation. Normal operating times are max.
25 seconds (MD) and 55 seconds (MLD), and the operating
time is limited to three minutes (see section
6.4 Description of
fault indications , fault code F011).
• automatic test runs (2 seconds) during long periods of
inactivity (24 hours after last operation)
• re-starting delay up to 45 seconds after returning from power
cut-off to mains operation (in order to even out the mains load
when several appliances are started up at the same time)
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