BRONKHORST®
Page 16
EL-FLOW
Base
Series Mass Flow Controllers
9.17.061
3.3 Digital communication protocol detection
(Flow-BUS RS232 or MODBUS RS485)
According to the pin-designation both RS232 and RS485 are assigned to the same pins.
At each power-on of the EL-Flow Base instrument the digital communication protocol from the master (PLC/PC)
must be detected by the EL-Flow Base instrument. This auto detection cannot be switched off or by-passed.
Description
PLC / PC
PLC / PC
Valid answer
within 100 ms
No
Initialisation
Send request to
read the
Measure value
Protocol Detected
Yes
Wait 100 ms
Bronkhorst
HIGH-TECH
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Base
EL-FLOW
mass flow meter/controller
received data is
recognized within
particular
frame?
No
Valid message
received within 660 ms?
Protocol Detection
in EL-FLOW Base
RS232 FLOW-BUS
110 ms
RS485 Modbus-RTU
110 ms
RS485 Modbus-ASCII
110 ms
Protocol and time frame (ms)
Detected Protocol
660 ms
Yes
Protocol Detected
Yes
No
Answer is sent
At each power-on of the
EL-Flow Base instrument a
protocol detection routine
is started and the
communication lines switch
each 110 ms between
RS232 FLOW-BUS, RS485
Modbus-RTU and RS485
Modbus-ASCII .
If received data is recognized
within the particular time
frame of a protocol then it
will immediately switch to
this protocol for 660 ms.
If now a valid message is
received the instrument will
answer (reply) to this
message and stay in the
detected protocol.
The protocol is detected.
The instrument will
remember the detected
protocol as long as the
instrument is powered.
