Rockwell Automation T7488, T7488A User Manual

ICS Regent + Plus

PD-7033

Monitored Guarded Output Modules

24 VDC, 110 VAC and 120 VDC

(T7481/T7481A, T7484 and T7488/T7488A)

Issue 2,

Monitored Guarded output modules provide Guarded control and line monitoring for sixteen field loads. Three typ modules are available for interfacing to outputs powered from 24 VDC, 110 VAC, or 120 VDC field power supplies. These modules are called Guarded because each module's dual redundant design ensures that no single fault within the module will inadvertently apply power to an output. These modules also monitor the output field wiring for open and short circuit faults. Individual output line status is available to application programs.

March, 06

es of

Features

Sixteen Guarded outputs (in two groups of eight).

•

Fault tolerant operation when connected in parallel with another module of the same type.

•

Hot-replaceable.

•

Complete, automatic testing of all output circuits.

•

Automatic line monitoring detects open and short field wiring circuits.

•

Individual front panel indicators on each module show module fault/active status and shutdown state; addi show output status and load/fuse fault for each point.

Fuses accessible from front panel.

•

2500 minimum electrical isolation between field and logic circuits.

TÜV certified, Risk Class 5.

Each module's triplicated Safetybus interface ensures that no Regent system failure will inadvertently apply power to an

tional indicators

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Monitored Guarded Output Modules

(T7481/81A, 84, and 88/88A)

output. E circuits ensure that each module operates in a fail-safe manner.

Two monitored Guarded output modules can be connected in parallel to obtain fault tolerant control of power to loads. In this parallel module configuration, either module can be removed and replaced while the other Guarded module continues to control the loads without interruption.

Module Operation

A block diagram of a typical monitored Guarded digital output module is shown in Figure 1.

xtensive fault detection and redundant critical

Figure 1. Block Diagram of a Monitored Guarded Digital Output Module.

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Monitored Guarded Output Modules

Case

Commanded

Output State

Switch

Failed

State

Actual

Output

to Load

Remarks

1 On

On On

Continued correct control. Automatic testing detects stuck-on switch. If output is subsequently commanded off, output will turn off.

2 On

Off Off

Fail-safe output. Automatic testing detects stuck-off switch.

3 Off

Off

Continued correct control. Automatic testing detects stuck-on

switch. If output is subsequently commanded on, output will turn on.

4 Off

Off Off

Fail-safe output. Automatic testing detects stuck-off switch. If output is subse

quently commanded on, output will remain off.

The processor modules send triplicated write data commands over the I/O Safetybus to the monitored Guarded output module. Onboard the output module the triplicated data are routed to two independent voters which provide voted data to associated field programmable gate arrays (FPGA). Each FPGA independently operates one of the two output control switches. The two out the load.

put switches are connected in series with

When both output switches are on, current will flow through the output and energize a field load. If either switch is off, current will not flow through the output and the load will be de-energized. This combination of series output switches and independent drive signals produces fail-safe activation of the load. Single failures can only affect one of the output drive signals or switches. A single failure will result in either continued correct control Table 1.

(T7481/81A, 84 and 88/88A)

or a fail-safe output as shown in

Table 1. Output States After Switch Failure.

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To achieve fault tolerance, two monitored Guarded output modules are used with their outputs connected in parallel. This configuration provides for continued correct control even

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Monitored Guarded Output Modules

when one output switch fails off (cases two and four in Table 1

). The module failure is automatically detected and the module can be removed and replaced without interrupting output control.

(T7481/81A, 84, and 88/88A)

Testing and Diagnostics

Automatic testing is performed on the monitored guarded output modules as well as the field load connections.

Module Testing

Each voter and FPGA logic section of the Guarded output modules are automatically tested by the processor modules. Discrepant data are sent through one of three legs of the I/O Safetybus to determine whether the module’s voters are able to outvote the incorrect data. A failure to return the correct majority-voted result to the processors produces an I/O module error indication at the processor modules and a module fault indication at the I/O module.

Each type of module has a unique identification code that is read by the controller. This code lets the controller know which type of module is installed in each I/O chassis slot and how to address that module and its points specifically. If a module is removed, or is replaced with a module of a different type, the

processor modules will indicate an I/O module error.

Loopback logic tests periodically write data to the module and then read it back to determine whether the module’s I/O bus interface logic is functioning correctly.

Output Circuit Testing

The output circuits of the monitored guarded output module are automatically tested to detect failures in the redundant output switch circuits on-board the module and also to detect open and short circuits in the output field wiring and load devices.

Output Switch Testing

To detect a failure in the redundant output switch circuits, each output switch is checked for turn-on and turn-off capability. Periodically, each output switch circuit on the module is tested for its ability to change its current state.

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Monitored Guarded Output Modules

During testing, the output state is changed; outputs that are on are turned off and outputs that are off are turned on.

When two monitored guarded output modules are wired in parallel for fault tolerance, the output circuit testing of the dual modules is coordinated. The test coordination is automatically performed by the system when the modules are properly configured for dual mode (see Configuration, starting on page 17). When dual modules are tested, the second module’s outputs are turned off momentarily while the first module’s outputs are tested. Subsequently, the first module’s outputs are turned off while second module’s outputs are tested.

When an output switch is tested, the test pulse duration is nominally 250 msec, and is insufficient to affect the state of most field loads. With modules configured in dual mode, the maximum test pulse may be 425 msec if one module has a switch failure. The output circuit test interval will range from 1 to 60 seconds, depending on the quantity of I/O configured in the system.

(T7481/81A, 84 and 88/88A)

If an output switch doesn’t change state when tested, an output switch fault is detected. An output switch failure is annunciated as a module fault. An I/O

module fault is indicated by the module FAULT LED on the module, the red I/O fault LEDs on the processor modules and the system control relay fault bit for the module assembly and slot.

Load and Fuse Monitoring and Testing

During output switch testing, the module also monitors the change in current flow in the field power for the outputs. The sensed state changes of the output switches and the field power current are reported back to the processor modules. The triplicated processor modules use this inform

ation to identify if an open load, shorted load or blown fuse condition exists.

Any of these load/fuse fault conditions are annunciated via the LOAD/FUSE fault LEDs on the face of the module and the Fault Name variables configured for each point. Load/Fuse faults are not reported as module faults and so do not turn on the red Module FAULT LED or associated system variable control relay fault bit. The Fault Name variables should be

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Note:

Monitored Guarded Output Modules

monitored by the application program or external operator interface equipment to dispatch maintenance personnel to correct the field connection problem.

Field faults such as open load, shorted load, blown fuse and absence of field power, will mask an output switch fault. When load/fuse faults are detected, they should be repaired as soon as possible.

If the health of spare, unused output points is important, then a minimum load device should be connected to these points.

(T7481/81A, 84, and 88/88A)

Front Panel

Figure 2 shows the physical features of the monitored Guarded output modules. The front panel of each module contains a module active and fault status indicator, a shutdown indicator, as well as output fuses, output status indicators and load/fuse fault indicators for the output circuits.

Active/Fault Status Indicators

These green and red LEDs indicate the overall health of the module and output circuits. During normal operation, the green ACTIVE indicator flashes at the controller's scan rate. If a module fault is detected, the red FAULT indicator turns on and the green ACTIVE indicator turns off.

Shutdown Indicator

Upon loss of communications with the controller, output modules enter either a shutdown or hold fault mode. If the I/O unit is set to shutdown, the red SHUTDOWN indicator will turn on when communications with the controller are lost. If the I/O unit is set to hold, the SHUTDOWN indicator will always be off (see page 16, Fault Mode Jumper).

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Note:

When the module is installed in the I/O chassis or when logic power (from the I/O power s the module, it will be in the shutdown mode until the first output scan, regardless of the fault mode jumper settings. Also, removing two I/O transceiver modules, two I/O power supply modules, or two power legs will cause the module to be in the shutdown mode.

(T7481/81A, 84 and 88/88A)

upply modules) is first applied to

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Monitored Guarded Output Modules

(T7481/81A, 84, and 88/88A)

Figure 2. Monitored Guarded Output Modules.

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