Chapter 1. Modbus Communications
2
Communications Options User’s Guide
1.2
Installing the MODBUS Option Card
IMPORTANT:
The installation information presented here supersedes the information in the standard flowmeter
User’s Manual.
The modified flowmeter uses the RS485 standard for MODBUS communications. This standard allows up to 32 nodes
(drivers and receivers) on one multidrop network, at distances up to 4,000 ft (1,200 m). To connect the instrument(s)
to the host system, Panemetrics recommends using a 24-gauge (24 AWG) twisted-pair cable with a characteristic
impedance of 120 ohms and a 120-ohm termination at each end of the communications line.
The MODBUS option card must be plugged into either slot 5 or slot 6 of the flowmeter. On the option card, pin 1 is the
[TMT-]
inverting or negative connection and pin 2 is the
[TMT+]
non-inverting or positive connection. To link the
flowmeter to the control system, connect the two wires of the twisted-pair cable from these terminals to the
corresponding terminals at the control system.
Note:
If two MODBUS option cards are installed in the flowmeter, only the card in slot 5 is activated.
1.3
Setting Up MODBUS Communications
To set up MODBUS communications, enter the
User Program as described in your Programming Manual. Then, refer to
the
menu map in Figure 2 on page 21 and complete the following steps:
Note:
Any time the following settings are changed, the flowmeter must be rebooted to load the new settings into
the option card.
IMPORTANT:
The serial port settings of the flowmeter must match those of the MODBUS control system.
The available RS232 baud rates are 300, 600, 1200, 2400, 4800, 9600, and 19200.
PROGRAM Start
Press the [
key and then the
[F3]
key to select the
COMM
submenu. (On a two-channel
flowmeter, pressing the [
key and the
[F3]
key accesses
the
GLOBL menu. Then press
[F4]
to select the
COMM
submenu
.)
PROGRAM
status
ACTI
V
SYST
M
PIPE
I/O
COMM PROGRAM
[This baud rate applies only to
the RS232 serial port.] Press the
[
until the desired RS232
baud rate appears on the
option bar and press the
appropriate
[Fx]
function key
to select it.
PROGRAM
Comm port
BAUD RATE
current value appears here
4800
9600
19200
