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Analog Value Processing
Selective Sampling
FB 250 permits reading of an analog value with selective sampling. Setting the "EINZ" parameter
to "1" causes the analog input module to convert the analog value of the selected channel to a
digital value immediately. During conversion (approximately 60 msec.), no further sampling
operations involving this module may be initiated. Consequently, the function block that is pres-
ently active sets the TBIT to "1" until the converted value is read in. The TBIT is reset upon comple-
tion of selective sampling is terminated.
Note
The 466-3LA11 analog input module has no overrange! When the measured value
reaches the nominal range limit, the overflow bit is set.
If you use standard FB250 (NAME:RLG:AE) of CPUs 941 to 944 for reading in the analog
values in the case of the 466 module, you must take account of the following:
•
Bipolar measuring range:
If the measured value reaches the nominal range limit, the BU (range violation)
parameter is set. The analog value read in is then invalid !
•
Unipolar measuring range:
If the measured value reaches the midpoint of the nominal range, the
BU parameter is set. The measured value read in is then valid !
Outputting an Analog Value
Use function block FB251 to output analog values to analog output modules. Specify the module's
type of analog representation (channel type) in the KNKT parameter. Values from the range
between the "lower limit" (UGR) and the "upper limit" (OGR) parameters are converted to the
nominal range of the relevant module using the following formula:
For channel type 0 (unipolar representation):
For channel type 1 (bipolar representation):
XE is the digital value specified in the function block and
Where
xa
is the value output to the module.
10-62
-FB251-
1024 ·(XE-UGR)
xa =
OGR-UGR
1024 ·(2 ·XE-OGR-UGR)
xa =
OGR-UGR
S5-115U Manual
EWA 4NEB 811 6130-02b
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