535-PROF User's Manual
Chapter 7
113
Applications
2. Set
OFFSET
. This parameter either adds or subtracts a set value from the
process variable reading in engineering units. For example, if the thermo-
couple was always reading 3° too high, the parameter could be set to “–3” to
compensate.
3. Set
GAIN
. This multiplies the deviation from the low end of the process vari-
able range by the gain factor and then adds it to the value of the low end 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 vari-
able reading is 472, a
GAIN
of 0.995 would yield an adjusted process vari-
able 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.
U. 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 application engineer.
Hardware Configuration
•
This optional features 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 1200 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 shes.
Setting this to MANUAL brings up the following parameters.
NOTE: PV1 GAIN
is only available if
using a linear voltage or current input.
