CG Drives & Automation 01-7492-01r1 Main Features 71
7.5 Load Monitor and
Process Protection [400]
7.5.1 Load Monitor [410]
The monitor functions enable the AC drive 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 AC drive by the calculated motor shaft
torque. There is an overload alarm (Max Alarm and Max
Pre-Alarm) and an underload 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
measuring 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,
minimum alarm and minimum pre-alarm.
Fig. 82 gives an example of the monitor functions for
constant torque applications.
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