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Analog Value Processing
S5-90U/S5-95U
Accuracy of the Analog Value Read
In order to establish the accuracy of an analog value (actual analog value), you have to calculate the
absolute error of the analog value.
Use the formula below to determine the absolute error of the analog value read in:
Absolute error=
Nominal analog
input value
Operational limit in %
100%
Please refer to the Technical Specifications for the PLC (see Appendix B) or the respective analog
input module (see Chapter 15) for nominal value and operational limit of the analog input.
The actual analog value is within the following range:
Value
read
-
Absolute
error
Actual
value
Value
read
+
Absolute
error
Actual value = Value read ± Absolute error
Example:
The analog value of 9.7 V was read in at a 4 x ± 10 V analog input module. The
nominal value for the analog input is ± 10 V. The operational limit for this module is
± 0.45 %. Determine the accuracy of the analog value.
Absolute error=
=
0.45%
100%
0.045 V
a a a a a a a a a
a a a a a a a a a
a a a a a a a a a
a a a a a a a a a
a a a a a a a a a
10 V
Actual
value
9.7 V - 0.045 V
9.7 V + 0.045 V
Actual analog value
= 9.7 V ± 0.045 V
The accuracy of the analog value varies within the range of ± 0.045 V.
12.1.4 Using Analog Inputs of the S5-95U as Additional Digital Inputs
By performing the following simple trick, you can also use the analog inputs of the onboard I/Os as
digital inputs:
Connect sensors with signal voltages > 10 V to analog inputs of the onboard I/Os (assign
channels in ascending order!).
Even when using the analog inputs as digital inputs, you still have to adhere to the installation
guidelines for the analog signal leads (e.g. use shielded cables).
Parameterize the analog inputs in DB1 (precondition for cyclic reading).
Program a scan of bit 0 of the input word assigned to the respective analog input in your control
program (overflow (OV) bit):
OV bit = 1 Signal state "1"
OV bit = 0 Signal state "0"
In this way, you have eight additional digital inputs at your disposal!
12-8
EWA 4NEB 812 6115-02b
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