KROHNE VFM 5090 EN - Manual (Page 24)

where,
Measured Value Numeric value of measured parameter as displayed in numeric field.
<SP> ASCII space character.
unit Unit of the measured value.
<CR> <LF> ASCII carriage return and line-feed sequence.
#nn Err# nn is the number of errors detected by the instrument.
error mesg. Error message as appears in the alphanumeric line of display.
examples -
1234.56 <SP> <SP> m3/hr <CR> <LF>
# 1 Err# <SP> <SP> LOW FLOW <CR> <LF>
Note that the actual number of characters in each format is not fixed and depends on the contents of Measured
Value, unit and error mesg. fields. The user system may use the 2 space characters and CR, LF characters as
delimiters for fields.
2. RS-485 OUTPUT
The RS-485 output option provides a means for communication of measured values to remote system such as
steam flow indicator. At present, this communication is in one direction only [from VFM5090(I) to remote
system]. Measured Values as well as Error Messages which appear on the instrument display in the normal
measurement mode are output on RS-485 line. When the RS-485 output option is present; the usual frequency
output function cannot be used.
2.1 RS-485 OUTPUT
The RS-485 output is galvanically isolated from all inputs and output circuits but not from current output.
Therefore, only one grounded receiver may be connected to either RS-485 output or current output.
·
·
·
Operating data for RS-485 output is not programmable as in case of current or frequency output. VFM
5090(I) always uses the following operating data : 1 Start bit, 8 Data bits, Odd Parity, 1 Stop bit at a baud rate
of 1200 bits/sec.
Connection diagram for RS-485 output is given below. Please note that the RS-485 output uses the same
terminals as used by the Frequency output. Consequently, when the RS-485 option is present, frequency output
function can not be used.
5
+ 6
- 4
TX+ 4.1
TX- 4.2
GND
2.2 CHARACTER FORMAT
Measured values or Error messages which appear on instrument display in normal measuring mode are coded as
series of 8-bit characters or “bytes”. These are transmitted serially, using a conventional UART (Universal
Asynchronous Receiver/Transmitter) function to serialize each byte. As in RS-485 or other asynchronous
communication, a start bit and stop bit are added to each byte. This allow the receiving UART to identify the start
of each character.
A single 8-bit byte is sent as the following sequence of 1’s and 0’s.
0 DO D1 D2 D3 D4 D5 D6 D7 P 1
Odd
Start bit <------------------------ 8 Data Bits ------------------- > Parity Stop bit
Baud Rate is 1200 bits/sec.
All characters are encoded in ASCII character format.
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