User`s manual

535 User's Manual Chapter 7 99
Applications
of the range to arrive at the adjusted process variable value.
For example, if the process variable range is 50 to 650 and the process
variable reading is 472, a PV GAIN of .995 would yield an adjusted process
variable equal to [(472 – 50) x .995] + 50 = 470.
With a combination of both offset and gain factors, just about any inaccuracy
in the sensor or transmitter can be compensated.
T. SERIAL COMMUNICATIONS
The serial communications option enables the 535 to communicate with a
supervisory device, such as a personal computer or programmable logic
controller.
The communications standard utilized is RS-485 which provides a multi-drop
system that communicates at a high rate over long distances. Typical limitations
are 32 instruments per pair of wires over a distance up to 4000 feet.
The 535 uses a proprietary protocol which provides an extremely fast and
accurate response to any command. Cyclic redundancy checking (CRC)
virtually ensures the integrity of any data read by the 535. Through
communications, there is access to every Set up, Tuning and Operating
parameter. For details on the 535 protocol, contact a Moore Industries
application engineer.
Hardware Configuration
• This optional feature is only available if ordered originally from the factory.
The circuitry for communications is contained on a modular circuit board
that plugs into the Microcontroller Circuit Board, Refer to the order code in
Chapter 1 for details.
Software Configuration
1. Access the SER. COMM. menu.
2. STATION specifies the unit’s station address. It is the only way one 535
can be distinguished from another. Each 535 on the same RS-485 interface
must have a unique station address.
3. Choose a BAUD RATE from 1,200 to 19,200. In general, select the highest
value. However, every instrument on the RS-485 interface must be set to
the same baud rate.
4. CRC indicates the cyclic redundancy checking feature. If the host supports
it, activating this option is recommended.
5. When the 535 senses that communications is lost, it can go to a
predetermined state (called “shedding”). The SHED TIME parameter sets
the length of time that communications can be interrupted before the
controller sheds. Since the 535 is a stand-alone controller, it does not depend
on communications to operate. Therefore, if the “shed” feature is not needed,
set it to OFF.
6. SHED MODE designates the mode to which the controller goes after it
sheds. Setting this to MANUAL brings up the following parameters.
7. Use SHED OUT to specify an output level if the unit sheds and trips to manual
control.
8. To specify a control setpoint (in case the host is supervising the setpoint) if
the 535 sheds, Set SHED SP to DESIG. SP and then, set the parameter