ICS Triples T3420A Analog Input Modules

Analog input modules provide data input for a maximum of 16 field analog signals per module.

Two types of modules are available: one for high noise immunity (60 Hz rejection) and one with low noise immunity (fast response).

Analog Input Modules (T3420A, AF)

2 Industrial Control Services prevent the controllers from receiving erroneous data from a faulty input module.

Three analog input modules can be connected in parallel to obtain fault-tolerant input sensing.

In this triple module configuration, a failed module can be removed and replaced without interrupting the input signals.

Block Diagram of Analog Input Module T3420A

Analog field signals are conditioned and multiplexed into an analog-to-digital (A to D) converter and converted into 12-bit digital data.

These digital values are stored in the module’s RAM.

The digital logic circuits are optically isolated from the analog field signals to protect the logic circuits from external field signal transients and overvoltages.

The processor modules send triplicated read data requests to

the analog input module over the I/O Safetybus.

The processors’ addressing data and data read requests are voted by the module (preventing I/O Safetybus failures upstream from the module from affecting module operations).

The voted result is then passed to the I/O bus interface logic.

After receiving the voted data read request, the I/O bus interface logic retrieves the analog data values from the RAM and places the data into the module’s three bus drivers.

Each of the three bus drivers is independently powered and controlled (by the I/O transceiver modules) — preventing failures in a single driver from propagating to the other two /O busses.

The bus drivers then transmit the data via the backplane I/O Safetybus to the I/O transceiver modules which, in turn, transmit the data to the processors.

The 12-bit analog input data is packaged as a 16-bit integer.

In this format the analog data is the least significant bits, providing analog input data ranging from 0 to 4095.

Two of the remaining four bits are used to flag alarms as shown in

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