HF scientific MicroTOL Online Turbidimeter old series- 0-1000 NTU - Manual (Page 30)

MICRO TOL (12/04)
Rev. 2.7 24
Communication Protocol: The originating instrument (master) has a designated address
of 00 hex and each instrument has a designated address from 01 hex to FF hex. The
communication protocol is as follows: the master computer will send out a 5 BYTE
instruction to the instrument to request data and the correct instrument will respond with
a 18 BYTE return message. To ensure a smooth transition of information each
instrument is designed with a 100-200 ms hang up time: the instrument waits 100-200 ms
before switching from receive to transmit to send the information to the master computer.
The 5 BYTE message sent by the master computer is detailed as follows:
BYTE #1 is an attention character (3A in hex format)
BYTE #2 is the native address of the master instrument that is requesting
information from the instruments in the RS485 loop. This address is 00 hex by
definition (sent in hex format).
BYTE #3 is the address of the instrument being queried (sent in hex format)
BYTE #4 is the command/request to be serviced. 00 hex is the request to have
the instrument report the current turbidity level (sent in hex format)
BYTE #5 is the Check Sum of the previous 4 bytes (sent in hex format). Note
that 1 hex is added to the sum as an offset level.
When a command of 0 hex is issued by the master computer, the instrument that was
addressed will provide an 18 BYTE return message. This message is detailed as follows:
BYTE #1 is an attention character (3A in hex format)
BYTE #2 is the native address of the instrument that is responding (sent in hex
format).
BYTES #3-10 represent the current turbidity value (including decimal place) sent
in hex. All hex values should be converted to ASCII. Any unused bytes
(depending on selected resolution) are filled to the right with spaces (20 hex).
BYTES #11-13 represent the engineering units measured with this instrument:
‘NTU’ (sent in hex format). All hex values should be converted to ASCII.
BYTES #14-15 represent the instrument status WORD in hex format (high BYTE
first). This provides information on the mode that the instrument is currently in.
BYTES #16-17 represent the instrument warning status WORD in hex format
(high BYTE first). This status WORD provides detailed information on warnings
that the instrument has stored. If this WORD is 0 hex then the instrument is
operating with no warnings or problems observed in operation.
BYTE #18 is the Check Sum of the previous 17 bytes (sent in hex format). Note
that 1 hex is added to the sum as an offset level.
The Baud rate used in this feature is the same as the baud rate set in the previous section
on automatic/timed printouts. The other parameters for the digital communication are 8
bit, no parity and one (1) stop bit.
An optional PC software package, called HF ONLINE (HF catalog # 19783) allows for
an interface with up to 255 Micro TOL’s for the purpose of data logging. This package is
similar to a small SCADA system and operates by communicating over the interface.