Johnson Controls Frick QUANTUM LX, Setup

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QUANTUM™ LX COMPRESSOR CONTROL PANEL
COMMUNICATIONS SETUP
090.020-CS (APRIL 13)
Page 35
SECTION 3
QUANTUM™ LX ALLEN-BRADLEY COMMUNICATION
QUANTUM™ LX ALLEN-BRADLEY COMMUNICATION
This section contains programming examples for reading
data from and writing data to the Frick Quantum control
panel from an Allen Bradley (AB) SLC500 or PLC5 proces-
sor. Allen Bradley (AB) RSLogix500 programming soft-
ware has been used for the following examples, however,
these examples can also be used for the AB RSLogix5
software.
Overview Of Half And Full Duplex Theory
To provide for the reading and writing of data to
Quantum™ LX panels using Allen-Bradley communi-
cation, the Quantum™ LX has an Allen-Bradley DF1
communication driver that recognizes either half or
full duplex SLC 500 protected typed logical read and
write commands (either half or full duplex must be
selected). Half-duplex simply means that data can
only be sent in one direction at a time (the concept
of how a walkie-talkie works). Using full-duplex, data
can be sent and received simultaneously (the
concept of how a telephone works). This is a
Leader
/
Follower
multi-drop communication
method.
The Quantum™ LX talks Allen-Bradley SLC protocol
and is programmed to resemble an Allen-Bradley
SLC500
follower
station. The customer’s PLC or
DCS must be setup to initiate the reading and writing
of data to a Quantum™ LX. The Quantum™ LX does
not initiate any communications. The panel ID
number is used as its station address and the target
node. With the AB PLC, the MSG (Message)
instruction is used to send read and write requests. A
DCS (Distributed Control System) will use a SLC 500
DF1 protocol driv-er to send protected typed logical
read with 3 address fi elds and protected typed logical
write requests with 3 address fi elds to a Quantum™
LX. Fifty (50) data elements can be read with one
read.
Setpoints are changed by sending a write
com-mand to one element. Changing a setpoint
causes the Quantum™ LX to save the new setpoint
to Flash memory (non-volatile memory).
Be careful not to continuously request a
setpoint change. It is to be expected that
communications may slow down during the
process of writing set-points or clearing alarms.
Both of these processes involve writing to either
EEPROM or Flash Memory and does take some
time. If communication requests are being sent
faster than once every couple of seconds, there
will be temporary slowdowns during these
processes.
Additionally, keeping the Quantum™ LX busy writing
to Flash memory will interfere with the communica-
tions to its I/O Boards. A communication failure to
an I/O board will cause the compressor to shutdown.
Control commands such as starting the compressor
are also sent with a write command. For more detail
and a list of the data, reference the Quantum™ LX
Data Table section. For details about the actual pro-
tocol, reference the AB publication 1770-6.5.16 DF1
Protocol and Command Set Reference Manual .
Because overrun can occur, the baud rate and
commands should be setup to produce the
most
desired throughput. The
leader
station should have
the Stop Bit and Parity set to match the
Quantum™ LX, Duplicate Detect disabled, and
Error Detect set for BCC or CRC.
When communication is between either your
programming software and a Quantum™ LX or an
Allen-Bradley PLC and a Quantum™ LX on a
multi-drop
link, the devices depend on a DF1
Leader
to give
each of them polling permission to transmit in a
timely manner. As the number of Quantum™ LX
followers increase on the link, the time between
when each panel is polled also increases. This
increase in time may become larger if you are
using low baud rates. As these time periods grow,
the timeouts such as the message timeout, poll
timeout and reply timeout may need to be changed
to avoid loss of communication.
ACK Timeout - The amount of time in 20
millisec-onds increments that you want the
processor to wait for an acknowledgment to the
message it has sent before the processor retries
the message or the message errors out.
Reply Message Wait Time - De fi ne the amount of
time in 20 millisecond increments that the
leader
station will wait after receiving an ACK (to a leader -
initiate message) before polling the remote station
for a reply. Choose a time that is, at minimum, equal
to the longest time that a remote station needs to
format a reply packet. Some remote stations can
format reply packets faster than others.
Message Timeout - De fi nes the amount of time in
seconds that the message will wait for a reply. If this
time elapses without a reply, the error bit is set,
indicating that the instruction timed out. A timeout of
0 seconds means that there is no timer and the
message will wait inde fi nitely for a reply. Valid range
0-255 seconds.
Note: Make sure the Allen-Bradley PLC and the
pro-gramming software is the most recent
software revision. Some revisions have been
made that do not