38 Main Features Emotron AB 01-4429-01r2
7.5 Load Monitor and Process
Protection [400]
7.5.1 Load Monitor [410]
The monitor functions enable the VSD to be used as a load
monitor. Load monitors are used to protect machines and
processes against mechanical overload and underload, such
as a conveyer belt or screw conveyer jamming, belt failure on
a fan or a pump dry running. The load is measured in the
VSD by the calculated motor shaft torque. There is an over-
load alarm (Max Alarm and Max Pre-Alarm) and an under-
load alarm (Min Alarm and Min Pre-Alarm).
The Basic Monitor type uses fixed levels for overload and
underload (pre-)alarms over the whole speed range. This
function can be used in constant load applications where the
torque is not dependent on the speed, e.g. conveyor belt,
displacement pump, screw pump, etc.
For applications with a torque that is dependent on the
speed, the Load Curve monitor type is preferred. By measur-
ing the actual load curve of the process, characteristically
over the range of minimum speed to maximum speed, an
accurate protection at any speed can be established.
The max and min alarm can be set for a trip condition. The
pre-alarms act as a warning condition. All the alarms can be
monitored on the digital or relay outputs.
The autoset function automatically sets the 4 alarm levels
whilst running: maximum alarm, maximum pre-alarm, min-
imum alarm and minimum pre-alarm.
Fig. 44 gives an example of the monitor functions for con-
stant torque applications
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