Rockwell-automation Current Input Module Uživatelský manuál stáhnout pdf (Strana 11)

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The module provides sixteen channels of 4Ć20 mA analog current

information to AutoMax and AutoMate systems. Each channel

consists of a pair of high impedance measurement inputs. The

sixteen current inputs share the same common. This analog common

has 2500 VAC of isolation from the system common. See figure 2.2.

An external userĆsupplied power supply is required for the 4Ć20 mA

transmitters. Terminal board assemblies (M/N 61C549 and 61C550)

have terminals available for both a primary power supply and a

backup power supply. The backup supply is optional. The two power

supplies are diodeĆisolated as shown in figure 2.2.

The sixteen pairs of inputs are multiplexed to an instrumentation

amplifier which drives a thirteenĆbit plus sign bit A/D converter.

The data register (registers 0 to 15) of a configured channel is

updated when the onĆboard processor converts and averages

together approximately 166 samples (60 Hz) or 200 samples (50 Hz)

of the channel input. 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. This overĆsampling of the analog inputs also simplifies

the filter requirements. A single pole analog filter is located on each

measurement input line. The line frequency filter can be disabled on

a perĆchannel basis via register 31 for a faster response time.

The module also contains three voltage references for A/D converter

calibration. These references are checked prior to each scan of the

configured channels, and the calibration coefficients are updated

accordingly. All nonĆzero references are derived from the A/D

converter's buriedĆzener reference. No potentiometer adjustments

are required to maintain the specified accuracy.

The onĆboard processor averages the raw A/D converter data,

linearizes the average using the calibration coefficients, and then

adjusts the reported output value per the userĆselectable scaling

values. If scaling values are not used, the reported output value will

be in the range 0 to 4095. This value will then either be written to the

appropriate channel data register (registers 0Ć15), or it will become

part of the running average specified in register 26. If a running

average is specified in register 26, the reported output value in the

channel data register is the averaged data value.

The module can also be configured, on a perĆchannel basis, to

provide square root extraction on the input signal. This provides flow

information directly from differential pressure inputs.

A broken wire from a transmitter is indicated through an outĆofĆrange

status bit in register 20. The module also 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.

All read operations on the module's memory include a parity test.

Failure of the parity test results in a system shutdown. Processor

modules can read all locations within the slot address but can only

write to registers 23 through 31.

The module will execute a full set of powerĆup diagnostics which

must execute successfully before the module can go into the run

mode.

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