16. Add-on Modbus RTU
67
Dr. A. Kuntze
I
Gutes Wasser mit System
Robert-Bosch-Str. 7a
40668 Meerbusch
+49 (0) 2150-7066-0 / Fax -60
www.kuntze.com
Registers four and five show the range of the temperature measurement, which is -30.0…140.0°C.
Example
for a numerical value with percentage flag:
The lower limit is listed as follows:
1.register: 6304, quantity of registers: 5
If you read these five registers, the response is as follows:
Reg. 1 (6304)
Reg. 2 (6305)
Reg. 3 (6306)
Reg. 4 (6307)
Reg. 5 (6308)
1111d (0457h)
258d (0102h)
1422d (058Eh)
65336d (FF38h)
1600 (0640h)
Value
Number of
decimal places
Code of unit
(pH)
Minimum of
range
Maximum of
range
The 258 in the second register means:
˃
Percentage flag is set, the value is increased by 256 (expressed as hexadecimal value 0102h).
The value is a percentage of the range. The true value has to be calculated from the range.
˃
After deducting the 256, in the second register remains a 2. Measured value and range limits have
to be divided by 100 to achieve two decimal places.
Registers 4 and 5 show the range of the lower limit, which is -2.00…16.00, and the third register shows
the unit pH. The value of the first register is 1111, which is 11.11% of the range. Calculate 11.11*(18)/100
and you will find that the value is 2pH above the minimum of the range = pH 0.
Note
Text variables have 25 registers, each containing one character expressed in
Ascii code. Text variables have no registers for decimal place, unit, or range.
16.3.2. Measured values, controller outputs and status of digital inputs and outputs
For measured value and temperature, an additional HOLD-value is given out. The HOLD-Value equals
the true value in the operation modes MAN and AUTO but is frozen whenever the instrument is set to
HOLD. We recommend the use the HOLD-value if you have set alarm values in the PLC that you do
not want to be activated during maintenance.
Note
The operation mode can be found in register 2240, refer to table “parameters”.
