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The output sacrifices a small amount of the resolution to provide a margin
of 2.5% to allow for system or calibration inaccuracies as shown below.
Resolution
20.5
20
Input Signal
Scaling
The digital data sent to the output is always scaled by the values set in the
maximum (S
) and minimum (S
max
scaling method. When digital data sent equals S
20.000mA and the digital data sent equals S
0.000mA. The following equations shows this relationship:
Iout = M x Module Data + B
where:
M =
(Smax – Smin)
20mA x (Smax + Smin)
B =
(Smax – Smin)
You can choose one of three scaling methods:
binary counts
default scaling
user scaling
User scaling is not available when you select discrete transfer mode.
The following table shows the output signals produced by various module
data values entered in each of the three scaling methods. In the user scaling
column, S
was set to 5000 and S
max
Output Signal
Output Signal
Binary Counts Scaling
Nominally +20.5mA
8395
20.000mA
8191
0.000mA
0000
1
Nominally -0.5mA
-0396
1
The actual output can never go negative. However, some of the output range is used to allow for zero offset
compensation.
Chapter 1
Introducing Block I/O
13 Bits
12.9 Bits
10
Nominal Range
) scaler values using a two point
min
, the output produces
max
, the output produces
min
20mA
was set to 0000.
min
Module Data
Default Scaling
10250
10000
00000
-00050
0.0 –0.5
User Scaling
5062
5000 (Smax)
2500 (Smin)
-2437
1-11
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