Scaling – Rockwell Automation 1771-IL/B , D17716.5.91 ISOLATED ANALOG INPUT Module User Manual
Page 31
Module Configuration
Chapter 4
4-7
Each channel has two scaling points, low and high. The signal value at
these points is fixed. For example, the high scaling point of a +10V output
channel always corresponds to an input signal equal to +10.000V.
To implement the scaling feature, you insert the minimum and maximum
scaled values in the appropriate configuration words.
The format of the scaling values is determined by the BTW format bit (bit
08, word 2). The range in BCD format is +9999. The range in binary
format is +32767.
For example, assume that at 0mA, the device connected to this input
channel is producing 0 psi, and at 20mA it produces 150 psi, and the
1771-IL/B range selected is 4 to 20mA. Extrapolation indicates that at
4mA, the device is producing 30 psi. By setting the low scale value of the
input to 30 and the high scale value to 150, this input channel will report
data in psi. For better resolution, you can multiply both of the scaling
values by the same multiplier as long as both scale values are in the range
of +9999 BCD or +32767 binary. By setting the low scale to 3000 and the
high scale value to 15000, you would report data in units of 0.01 psi
per count.
Maximum resolution can be obtained by setting the low scale value to
-9999 in BCD and the high scale value to +9999 in BCD (-32767 low and
+32767 high in binary).
For example, if in the 1 to 5V mode, the scaling points are 1 and 5 volts.
If you set the scaling to +32767, the maximum the module will display will
be 32767. If 5.1V is applied, the display will be 32767 and the overrange
bit for that channel will be set.
Note: To achieve the 0 to +10V range you must use bipolar scaling. Select
the +10V range and scale for + the actual intended range. If you need 0 to
100 gpm, set scaling values at -100 and +100. You will effectively be
creating a 0 to 10V range that is scaled from 0 to 100.
Implementing the Scaling Feature
You implement the scaling feature by:
1.
Inserting minimum and maximum scaled values in the appropriate
configuration words
2.
If using BCD, and any of the minimum or maximum values are
negative, set the appropriate sign bits in the minimum or maximum
sign bit words.
Scaling