Converting Voltage Values To Physical Values - Siemens SIMATIC S5 Manual

Special Functions for Plastic Machines

3.4.4 Converting Voltage Values to Physical Values

Channel 13 and comparator
Channel 13 is used to measure transducer signals. As standard, the input is equipped with a voltage
divider 400:1. For other applications, this divider can be changed (see C79000-B8576-C859 in
Part 2 of this manual).
The permitted input voltage with the 400:1 divider and 51.2 mV ADC sensitivity is 0 to 15.36 V
(= 1536 units on the ADC).
To take into account the transducer-specific data from measured value acquisition in the actual
value indication in message 17, a normalization factor and a matching value are required. The
normalization is performed by selecting bits A and B. The normalization factor and matching value
are entered in message 15, bytes 14/15.
The actual value appears in message 17, bytes 26/27 and is calculated according to the following
formula:
Example for the normalization and adaption of the actual value display for channel 13:
The connected voltage is 5200 mV, the desired display is 250.
This results in: 5200/250 = 20.8.
To represent the digit after the decimal point, you must multiply with 10 or 100 as the normalization
factor. It is not possible to use 1000 as the normalization factor, as the accompanying number range
is too small to represent 28.8 1000.
Then the normalization factor is 10 : A = 1, B = 0, matching value = 208 (D0hex)
The setpoint for the comparator in message 15, bytes 0 and 1 is calculated as follows:
IP244
4–104
C79000–B8576–C860–02