BRONKHORST®
9.17.061
EL-FLOW
Base
Series Mass Flow Controllers
Page 19
Termination resistors: RT1 and RT2
The termination resistors RT1 and RT2 must be placed only at the extreme ends of the data line (see
schematics above). The resistance value should be equal to the characteristic cable impedance. In case
of common cabling this should be:
RT1 = 121 Ohm
RT2 = 121 Ohm
Remark: RT1 and RT2 should be larger than 90 Ohm.
Biasing resistors: RB1 and RB2
The biasing resistors RB1 (pull-up) and RB2 (pull-down) must be added.
RB1 must be connected between the Supply Voltage (Us) and D1 Modbus (B/B'). The resistance value of
RB1 depends on the applied supply voltage, and is:
RB1 (Us = +24V) = 3480 Ohm
RB1 (Us = +15V) = 2210 Ohm
RB1 (Us = +10V) = 1210 Ohm
RB1 (Us = +5V) = 392 Ohm
RB2 must be connected between the D0 Modbus (A/A') and ground. The resistance value of RB2 is:
RB2 = 392 Ohm
3.5.2 Slave address, baud rate and parity setup
Default instruments will be delivered to customers on address 1 and with a baud rate of 19200 baud and
EVEN parity.
The slave address, baud rate and parity of the Bronkhorst® meter/controller Modbus slave can be
changed to fit the instrument in your existing Modbus network. Changing the slave address, baud rate
and parity can be done in the following ways.
Using RS232: FlowDDE
‘Off-line’ via the RS232 communication port by means of FlowDDE. This program can be used to
read/change parameters, including the slave address, baud rate and parity.
Connect your Bronkhorst®
meter/controller Modbus slave instrument to a free COM-port using the special cable with on one side
a T-part with male and female sub-D 9 connector and on the other side a female sub-D 9 connector (part
number 7.03.366). The single sub-D 9 connector should be connected to your COM-port and the female
sub-D 9 of the T-part to the male sub-D 9 of the instrument. Standard cables are approx. 3 meters.
Maximum length between PC and instrument allowed is approximately 10 meters.
Start FlowDDE and open communication via the menu (as shown below) or by pressing <F3>.
