Parameter Protection; Calculating The Gain And Offset Of Analog Values - Siemens LOGO! Manual

4.3.5

Parameter protection

In the parameter protection settings, you can determine whether or not the parameters can
be displayed and edited in LOGO! parameter assignment mode. Two options are available:
+: The parameter attribute permits read/write access in parameter assignment mode
(default).
-: The parameter settings are read–/write–protected in parameter assignment mode, and can
be edited only in programming mode. See the parameter protection mode example in the
Second circuit program (Page 83).
Note
Parameter protection covers only the "Set Param" window. If you embed variables of
protected special functions in a message text, the variables are still editable from the
message text. To protect these variables, you must also activate the protection of the
message text.
4.3.6

Calculating the gain and offset of analog values

A sensor is connected to the analog input and converts a process variable into an electrical
signal. This value of signal lies within the typical range of this sensor.
LOGO! always converts the electrical signals at the analog input into digital values from 0 to
1000.
A voltage of 0 to 10 V at input AI is transformed internally into a range of values from 0 to
1000. An input voltage exceeding 10 V is shown as internal value 1000.
Because you cannot always process the range of values from 0 to 1000 as predetermined by
LOGO!, you can multiply the digital values by a gain factor and then shift the zero of the
range of values (offset). This allows you to output an analog value to the LOGO! onboard
display, which is proportional to the actual process variable.
Parameter
Input voltage (in V)
Internal value
Gain
Offset
Mathematical rule
Actual value
(internal value at input Ax • gain) + offset
Gain and offset calculation
The gain and offset is calculated based on the relevant high and low values of the function.
Example 1:
The available thermocouples have the following technical data: -30 to +70 °C, 0 to 10 V DC
(i.e. 0 to 1000 in LOGO!).
Actual value
LOGO!
Manual, 10/2017, A5E01248535-AA
Minimum
0
0
-10.00
-10000
Ax =
= (internal value • gain) + offset, thus
LOGO! functions
4.3 Special Functions
Maximum
≥ 10
1000
+10.00
+10000
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