Rockwell Automation 1771-IL/B , D17716.5.91 ISOLATED ANALOG INPUT Module - Manual (Page 26)

Module Configuration
Chapter 4
4-2
During normal operation, the processor transfers from 1 to 37 words to the
module when you program a BTW instruction to the module’s address.
The BTW file contains configuration words, high and low channel alarm
settings, and calibration values for each channel.
When a block transfer write length of 0 is programmed, the 1771-IL
series B will respond with the Series A default length of 19.
Individual inputs are configurable to operate with any one of five voltage
or three current ranges. You can select individual channel ranges using the
designated words of the write block transfer instruction (Table 4.A). Two
bits are allocated for each channel. For example, for channel 1, set bits 00
and 01 as follows:
Table 4.A
Bit Settings for Voltage or Current Inputs
Bit 01 Bit 00 Voltage or current input
0 0 1 to 5 V DC, 4 to 20 mA 1
0 1 0 to 5 V DC, 0 to 20 mA 1
1 0 -5 to +5 V DC, -20 to +20 mA 1
1 1 -10 to +10 V DC, 0 to 10 V DC 2
1 Current input mode selected by configuration plug.
2
Configurable using bipolar scaling.
The 1771-IL/B has 16-bit resolution across the +10V range. For
compatibility purposes, the default scaling for all ranges is 12-bits (0-4095
or +4095). This allows the series B module to be directly interchangeable
with the series A module. To use the full 16-bit capability, scaling values
must be changed. Refer to “Scaling” later in this chapter.
Table 4.B shows the incremented voltage or current assigned to each bit for
the seven different input ranges. For example, if the channel 1 input range
is 0 to +5V and the actual incoming signal is at mid-range (+2.5V) the
value in the module’s data word, if using default scaling, would be 0000
1000 0000 0000 (binary) or 2048 (decimal). The input (default scaling) is
2048/4096, or 1/2 of full scale.
Input Range Selection