Tricon System Introduction

The Tricon is a state-of-the art controller that provides fault tolerance by means of Triple-Modular Redundant (TMR) architecture. TMR integrates three isolated, parallel control systems and extensive diagnostics in one control system. The system uses two-out-ofthree voting to provide high-integrity, error-free, uninterrupted process operation with no single point of failure.

The Tricon controller uses three identical channels. Each channel independently executes the control program in parallel with the other two channels. Specialized hardware/software voting mechanisms qualify and verify all digital inputs and outputs from the field, while analog inputs are subject to a mid-value selection process. Because each channel is isolated from the others, no single-point failure in any channel can pass to another. If a hardware failure does occur on one channel, the other channels override it. Meanwhile the faulting module can easily be removed and replaced while thecontroller is online without interrupting the process. Setting up control programs is simplified with the triplicated Tricon system, because it operates as a single control system from the user’s point of view. The user terminates sensors and actuators at a single wiring terminal andprograms the Tricon with one set of control program logic.

The Tricon controller manages the rest! Extensive diagnostics on each channel, module, and functional circuit immediately detect and report operational faults by means of indicators or alarms.

Termination Configuration Options  

Terminations are available in various factory configurations:

• Non-commoned Terminations can accommodate individual power supplies for each point.

• Commoned Terminations can support one power supply which is shared by multiple points. Points can be commoned in groups of 8 and groups of 16.

• Analog signals can be read as 3-wire transmitter inputs, voltage inputs or current inputs.

• Thermocouple terminations provide cold-junction temperature sensors and are available for either upscale or downscale burnout detection. For the model 3706A, upscale or downscale burnout detection depends on which termination panel is installed. For model 3708E, upscale or downscale burnout detection is configured with TriStation. 

The “Termination Options” table (on the next two pages) shows the available termination choices for each I/O module and gives the correct model number for each choice.

Dual Digital Output Module

The dual digital output (DDO) modules receive output signals from the main processors along a single parallel or series path, and applies a 2-out-of-3 voting process individually to each switch. The switches produce one output signal which is then passed to the field termination. While the quadruplicated output circuitry on TMR modules provides multiple redundancy for all critical signal paths, dual circuitry provides just enough redundancy to ensure safe operation. The dual module is optimized for those safety-critical control programs where low cost is more important than maximum availability.

The dual digital output modules have a voltage-loopback circuit which verifies the operation of each output switch independently of the presence of a load and determines whether latent faults exist. Failure of the detected field voltage to match the commanded state of the output point activates the LOAD/FUSE alarm indicator. 

In addition, ongoing diagnostics are performed on each channel and circuit of a dual digital output module. Failure of any diagnostic on any channel activates the Fault indicator, which in turn activates the chassis alarm signal. A dual module operates properly in the presence of most single faults and may operate properly with some kinds of multiple faults, but stuck-OFF faults are an exception. If one of the output switches has a stuck-OFF fault, the output goes to the OFF state and a glitch may occur during switch-over to a hot-spare module.

The dual digital output modules support hot-spare capability which allows online replacement of a faulty module. Each module is mechanically keyed to prevent improper installation in a configured chassis.

The dual digital output modules require a separate external termination panel (ETP) with a cable interface to the Tricon backplane. Digital outputs are designed to source the current to field devices, so field power must be wired to each output point on the field termination.