Cascade Controller Option
Operation modes
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Standard Cascade Control Mode
In standard cascade control, a frequency converter
with the Cascade Controller option card installed
controls a variable speed motor and is used to
stage additional constant speed motors on and
off. By varying the speed of the initial motor,
variable speed control is provided for the system.
This maintains constant pressure while eliminating
pressure surges, resulting in reduced system
stress and quieter operation.
The motors can be of equal or differing sizes. The
controller offers a selection of eight pre-defined pump
combinations. Selections allow mixing pumps of
100%, 200% and 300% capacity. This provides a
dynamic capacity range of 9 to 1. The VLT drives
internal PID controller directs the cascade option
card based upon the feedback signal. The cascade
controller will continue operation of the constant speed
motors to meet demand should the drive trip.
De-stage Timer
A de-stage timer takes effect in standard control
when the drive runs continuously at minimum speed
with one or more constant speed motors running.
Since a variable speed pump at minimum speed
adds no or very limited flow to the system, it is
advisable to stop a constant speed motor and
allow the drive to provide the required flow. The
de-stage timer is programmable to avoid frequent
staging of the constant speed motors.
When the master drive is the only one running, the
drives sleep mode can discontinue system operation
when not needed while staying ready to start on
demand. Variable speed control with fixed speed
motors optimizes energy consumption and avoids
damaging a pump running at near no flow condition
Level Control
With level control, multiple pumps can be used to
keep a constant level in applications such as a buffer
tank. Typically, a water level sensor provides a
feedback signal for the VLT
’
s built-in PID controller.
Precise level control is maintained in response to
the system setpoint. With a cascade controller,
additional fixed speed pumps will be staged on or
off, as required, to maintain level control.
Level Control in Standard Cascade Control Mode
MG.60.I3.02 - VLT is a registered Danfoss trademark
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