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Master/Slave Cascade Control Setup
Introduction
In Master/Slave cascade control operation, the
frequency converter with the cascade control option
card is the Master. The Master drive controls the
speed and staging on or off of up to four additional
adjustable speed drives. The Master drive exports
a pulse signal or analog speed signal through its
output relays to the slave drives. It is recommended
that a pulse signal be used for minimum electrical
noise and for precise drive control.
The Master drive and the slave drives are programmed
for different operation, although many parameters
are set the same. The Master drive is programmed
for closed loop operation and responds to system
feedback signals to meet the needs of the system.
The slave drives are programmed for open loop
operation and receive a variable speed signal and
stop/start commands from the Master drive.
Although pump applications are highlighted in this
chapter, the procedures and settings are nearly
identical for other applications. The feedback process
setup described, assumes that a pressure feedback
signal is measured at the outlet of the pumps.
Programming instructions:
Instructions for programming Quick Menu items
1-20 are presented in Chapter 6, VLT Drive and
Cascade Controller Card Setup. Parameters
1-20 must be programmed before programming
Master/Slave cascade control options.
The instructions in this chapter describe procedures
for programming both the Master and slave drives
for Master/Slave cascade control mode. Procedures
for programming are in the following order:
Initial Setup: Quick Menu items 1-20
Step 1: Master drive programming
Step 2: Slave drive programming
Step 3: Optimization of the process regulator
Alternate Programming
Optimizing the process regulator is performed after
system start up. The procedures are described
in Chapter 9, System Optimization.
Best efficiency:
Danfoss has available the Multiple Unit Staging
Efficiency Calculator (MUSEC), a free software
program available on the Danfoss website. By
46
Cascade Controller Option
entering pump and system data, MUSEC provides
the programmer with Master drive on and off staging
frequencies for each pump at optimal efficiency.
For a free download, go to www.danfoss.com
and enter MUSEC in the search box.
Sensor placement:
Best efficiency is attained when the pressure
transmitter is placed at the farthest significant load
in the system. This setup allows measurement of
actual system peformance. If this is not practical,
the pressure transmitter is usually placed close
to the discharge of the pumps.
The default feedback process described for setup
in this chapter is used when a pressure feedback
signal is measured at the outlet of the pumps. The
cascade controller uses the feedback to estimate the
setpoint required at various rates of flow. Setpoint 1
is the minimum pressure required when the system
is running with only the adjustable frequency drive
operating at full speed. Setpoint 2 is the maximum
pressure required when the system is running with all
pumps at full capacity. A theoretical value calculates
pressure loss in the system under minimum and
maximum loads. The controller adjusts the loading
based upon the number of pumps in operation.
When the pressure transmitter is placed at the farthest
significant load in the system, common in HVAC
applications, see alternative ways of programming
the cascade controller described in Alternate
Programming at the end of this chapter.
Although pump applications are highlighted in this
chapter, the procedures and setting are nearly
identical for fan applications, such as controlling
multiple cooling tower fans. Differences between fan
and pump settings are described in the procedures.
General information on how to program the adjustable
frequency drive through the local control panel keypad
are presented in Chapter 4, User Interface.
Initial Setup
Instructions for programming Quick Menu items
1-20 are presented in Chapter 5, VLT Drive and
Cascade Controller Card Setup. Parameters 1-20
must be programmed into the Master drive before
programming additional Master/Slave cascade
control options described below.
MG.60.I3.02 - VLT is a registered Danfoss trademark
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