Hach 911 User Manual page 97

Unit
CFM
CFH
CFD
CMS
CMM
CMH
CMD
GPS
GPM
D.10 Query
Start Slave
':' Address
Start
Slave Address
Function
Starting Address High
Starting Address Low
No. of Registers High
No. of Registers Low
LRC
Stop
Table 17 SCADA-Modbus Units of Measure Codes
Code
17
18
19
20
21
22
23
24
25
The Modbus ASCII query must take the form shown below that specifies the starting
register and number of registers to be read:
Start
Function
Address Address
(03)
High
For example, to read the level channel of the 940 Flow Meter, the query must be as
indicated in Table 18.
Table 18 Channel Query to Read Level (Example)
The master queries the flow meter using a Read Holding Registers request, which implies
a 4XXXX register reference, to slave device address 01. The message requests data from
holding registers 40007–40008 to obtain the level information, which requires two
registers to store the floating point value. Note that registers are referenced from zero in
the data field.
SCADA-Modbus® System Guidelines
Unit
DEGREE_F
MILS
VOLTS
FPS
MPS
PCT_O2
PCT_H2S
PCT_LEL
VDC
Start
No. of Pts. No. of.
High Pts. Low
Low
Code
42
43
44
45
46
47
48
49
50
LRC <CR> <LF>
':'
01
03
00
06
00
02
F4
<CR><LF>
95