3.8.1 Direct Current Input on the Analog (I/O) Module Y
External measuring transducers normally supply an output current of 0 to 20 mA
that is directly proportional to the physical quantity being measured – the
temperature, for example.
If the output current of the measuring transducer is directly proportional to the
measured quantity only in certain ranges, linearization can be arranged,
provided that the measured data input is set accordingly. Furthermore, for
certain applications it may be necessary to limit the range being monitored or to
monitor certain parts of the range with a higher or lower sensitivity.
By setting the value pair MEASI: IDC 1 and MEASI: IDC,lin 1, the user
specifies which input current I
DC
will correspond to the current that is monitored
by the Limit Value Monitoring function, i.e. I
DC,lin
. (These two setting parameters
refer to value pair number 1; setting parameters for value pairs 2 to 20 are
available, too.)
The resulting points, called “interpolation points”, are connected by straight lines
in an I
DC
‑I
DC,lin
diagram. In order to implement a simple characteristic, it is
sufficient to specify two interpolation points, which are also used as limiting
values (see Fig. 3-24, (p. 3-39)). Up to 20 interpolation points are available to
implement a complex characteristic.
When setting the characteristic the user must remember that only a rising/rising
or falling/falling curve sense is allowed (no peak or vee-shapes). If the setting
differs, the signal SFMON: Invalid scaling IDC will be generated.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
0 0.1 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.6
19Z5266A_EN
I
DC,lin DC,nom
/ I
I
DC,lin20
I
DC,lin1
I
DC1
I
DC20
I
DC DC,nom
/ I
Fig. 3-24: Example of the conversion of 4 to 10 mA input current to 0 to 20 mA monitored current, IDC,lin.
3 Operation
P631
P631/EN M/R-11-C // P631-310-650 3-39
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