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Appendix C
•
Remote Control and Monitoring of Vission 20/20 Panel
Vission 20/20 • Operation and Service Manual • Emerson • 35391SC 2.7
deadband region.
2. If the new target is > deadband region but < 10%
(full scale) away from the current position, then en-
ergize the capacity slide for a time that is propor-
tional to the amount it is away from the new target
position. To say it another way – the further you are
away from the new target position – the longer the
slide is energized in the proper direction. This con-
trol region is called the proportional band region.
3. If the new target is > 10% (full scale) away from cur-
rent position (greater than the proportional band
region) – then energize continuously.
There are mechanical properties that limit the speed at
which the capacity of the compressor can be changed.
The capacity slide actuators can only turn so fast. The
proportional change to the compressor capacity occurs
at a fixed rate.
Caphold and Operation with VFD
• Using a VFD with a compressor requires considering
the VFD capacity as part of the entire capacity of the
compressor. Typically, a VFD is operated from 50% to
100% speed, therefore the VFD is considered ½ the
total capacity and the slide valve movement is con-
sidered the other ½ of total capacity. When a VFD
is employed, the normal control method is to first
move the capacity slide from 0-100% when addition-
al refrigeration is required. When the capacity slide is
at 100% and additional capacity is still required, then
the VFD is ramped up in speed. It follows then that
the 4-20ma Caphold signal is broken down into two
parts:
• 4-12 mA = 0 -100 slide valve position
• 12-20ma = VFD minimum speed to VFD max-
imum speed.
Consideration should also be given so that when moving
the capacity slide valve from 0-100%, the actual corre-
sponding capacity of the compressor is not changing in
a linear relationship of 0-100%. The last 15% travel of the
slide valve results in a greater change of capacity than
15%. Integrators should realize that the caphold value
sent relates to slide valve “position” and not actual ca-
pacity of the compressor. For most purposes however,
assuming a linear relationship is adequate.
The rate at which the capacity slide moves from 0-100%,
and the rate at which the VFD increases speed from min-
imum to maximum is not the same. So there are two
different capacity profiles that the integrator needs to
consider.
Remote Enable Output
• When the compressor is off and in Remote mode, an
enable output will provide a signal to indicate that
the 20/20 is in a condition where it is ready to be
started. No start inhibit conditions exists, the 20/20
is not in anti-recycle mode, and there are no trips ac-
tive. If the compressor is able to be started, then the
Remote Enable output will go on. When the output
is on, then closing the Remote Start/Stop input will
initiate a compressor start.
NOTE
Once the compressor has started, the state of the
Remote Enable Output is indeterminate, and has no
meaning.
CONTROL SCENARIO
Once the Configuration Screen has been configured for
the desired type of Digital I/O control the Vission 20/20
needs to be placed in REMOTE mode. To do this, press the
green UNIT START button, then REMOTE. The Remote
Start-Stop input is now active. The state of the Remote
Enable Output should be determined by the controlling
device. When it is determined to be on, then the control-
ling device can energize the Remote Start-Stop input.
After the compressor has started, then the compressor
capacity is controlled by the selected option. Thought
should also be given as to how the compressor will be
restarted after a power failure occurs.
REMOTE MONITORING
• It should be noted that while the compressor is being
controlled (starting, stopping and capacity control)
via hard-wired inputs, the monitoring of compres-
sor operating parameters can still occur by using the
communication ports available in the 20/20. Remote
monitoring can be accomplished by utilizing either
the Ethernet communication port (via Ethernet I/P or
Modbus TCP/IP) or the serial port (via RS485 Modbus
RTU). For communication register information, refer
to Table D-1.
Summary of Contents for Vilter Vission 20/20
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