CTI 2550-A, Installation And Operation Manual

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2 C T I 2550-A Installation and O peration G uide
1.1.2 Input Connector for Channels 1-8
This connector provides wiring terminals for channels 1-8 for either voltage or current inputs.
1.2 Asynchronous Operation
The module operates asynchronously with respect to the PLC (a scan of the PLC and input sampling of
the module do not occur at the same time). Instead, the module will translate all analog inputs in one
module update (4 milliseconds maximum) and store the translated words in buffer memory. The PLC
retrieves the stored words from the module buffer memory at the start of the I/O scan.
1.3 Immediate I/O
The Model 2550-A Analog Input Module is fully compatible with the Immediate input instruction for
the SIMATIC® 545 and 555 PLCs.
1.4 Unipolar or Bipolar Mode
Each input channel may be configured to accept either bipolar or unipolar input signals. Selection of
unipolar or bipolaar mode is made via an internal jumper (see Section 2.3.3).
1.5 Voltage or Current Mode
Each of the module’s eight channels may be configured to receive either voltage or current analog input
signals. For unipolar input signals, the range is 0 to 5 VDC, 0 to 10 VDC or 0 to +20 mA. For bipolar
input signals, the signal range is -5 to +5 VDC, -10 to +10 VDC or -20 to +20 mA. Selection of
voltage or current mode and voltage range are made via internal jumpers (see Sections 2.3.1 and 2.3.2).
1.6 Digital Word Map
A unipolar analog input signal is translated into a 12-bit plus sign bit digital word. A bipolar input
signal is translated into an 11-bit digital word plus 1-bit for the polarity sign. Since the PLC requires a
16-bit input word, the 12-bit value from the converter is placed into a 16-bit word for transmittal to the
PLC. As shown in the following figure, of the four bits not used for the digital word, one is used to
show the sign of the word, one is used to note values which are “overrange”, and the remaining bits are
not used and are set to zero.