HF scientific 19944 Triple Validation Turbidimeter - 0-100 NTU - Manual (Page 28)

TVT2 (5/02)
Rev. 1.7 (.pdf) 23
Select the correct baud rate (1200, 2400, 4800, or 9600) for operation of the I/O port by
pressing either the
t or u button to change the displayed baud rate. When you have
selected the proper baud rate press the ↵ button to continue on to configure the security
access option. The other parameters for the digital communication are no parity and one
(1) stop bit.
Note: The information printed out in the timed printout has the format: x.xx NTU dd
Mmm yyyy hh:mm. The resolution of the turbidity level output is the same as the
resolution of the turbidity level on the display.
Optional Bi-Directional Communication: The instrument may be equipped with the
ability for bi-directional communication: this means that a remote unit can prompt the
instrument to send out the current turbidity levels via the RS 485. In order to do this you
must have ordered the instrument with the bi-directional RS 485 option. If you did, you
will be prompted to select the address of the instrument:
Here you can select the desired instrument address (1-255) using either the t or u
buttons. Once you are satisfied you can press the ↵ button to continue on to configure
the security access option.
Communication Protocol: The communication protocol used in the instrument is an
abbreviated version of the standard MODBUS protocol. The originating instrument
(master) has a designated address of 0 hex and each instrument has a designated address
from 1 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.