Rockwell Automation 61C542 Voltage Input module - Manual (Page 11)

2Ć3
2.2 Electrical Description
The module provides analog voltage information to AutoMax and
AutoMate systems. The module has sixteen singleĆended channels
which can alternately be configured as eight differential channels.
SingleĆended operation versus differential operation is programmable
on a perĆchannelĆpair basis via register 31.
Differential channel pairing is hardwareĆdefined as follows: channels
0Ć1, 2Ć3 ... 14Ć15, with the evenĆnumber channel being the plus or
high input. Each channel is a highĆimpedance measurement input.
No power is supplied from the module for use by the voltage
transmitters. See figure 2.2.
Each channel can be configured via register 31 as either bipolar, with
an input range of +/- 10 volts, or as unipolar, with an input range of
0 to 10 volts. All input channels are referenced to the same analog
common. All analog inputs must be within the +/- 10 volt range with
respect to analog common for proper operation. The analog
common has 2500 VAC of isolation from the system common.
Configured channels are sequentially multiplexed to an
instrumentation amplifier which drives a thirteen bit (plus sign) A/D
converter. Each input line contains a single pole, lowĆpass filter. The
onĆboard microprocessor also provides line frequency filtering on a
perĆchannel basis. It accomplishes this by converting and averaging
together channel input samples over 16.6 ms for a 60 Hz line or 20
ms for a 50 Hz line. In this manner, line frequency noise at the input
of the A/D converter is integrated out of the result that is provided to
the system. The line frequency filter can be disabled on a
perĆchannel basis to increase the data update rate.
The module contains three voltage references for A/D converter
calibration. These voltage references are checked prior to each scan
of the configured channels. An outĆofĆrange reference voltage will
force a module shutdown. These checks also provide constant
updating of the A/D converter's calibration coefficients. No
potentiometer adjustments are required to maintain the specified
accuracy.
The onĆboard microprocessor automatically adjusts the input
channel's data based on the calibration coefficients. The adjusted
input value is then scaled according to the userĆselectable values
located in registers 24 and 25. The default (unscaled) values in
registers 24 and 25 are 4095 and -4095, respectively. The scaled
result is then either written to the appropriate channel data register
(registers 0 Ć 15), or it becomes part of the running average specified
in register 26. If a running average value is used, the reported output
value in the channel data register is the averaged data value.
The module can also be configured to provide a square root
extraction value based on a channel's input data value. This provides
flow information directly from differential pressure inputs. Note that if
you select square root, you must be in unipolar mode.
The module provides high and low limit registers which can be set by
the user. Status registers then indicate when the desired high/low
values have been exceeded. A broken wire from a transmitter on a
configured channel is indicated by an outĆofĆrange status bit in
register 20.
All read operations on the module's memory include a parity test.
Failure of the parity test results in a module shutdown. Processor