PCC-III Digital Loop Controller

Multiple Loops: Due to its ability to handle several control loops, application of a single PCC-III may allow a reduction in the total number of controllers necessary for an installation. The large 160 function block configuration memory allows any function to be assigned to each block, providing unequalled flexibility and enough power to handle just about any boiler control strategy.

Expandable I/O: The wide variety of PCC-III option boards allows one to expand the I/O capabilities of a given controller to fit any application.  Refer to the specifications page for expansion card possibilities.  Up to 15 analog inputs can be used to support complex control strategies or satisfy data acquisition needs. The PCC-III can be equipped with up to 6 relay outputs. These outputs are rated for up to 8A inductive loads and can be used on most applications without external “helper” relays. Two ZP Oxygen Sensors can be connected to a PCC-III without any external Oxygen transmitter needed. Additionally, the PCC-III offers Triac outputs to drive reversible AC electric actuators, solenoids, horns and other devices. The “G” Triac Output option card includes a “position feedback” potentiometer or 4-20 mAdc inputs for closed loop servo positioning.

Multiple Function Generator F(x) Blocks: The F(x) block is used to “characterize” or “curve fit” an analog signal by allowing each value of the input to be assigned an independent output value. The PCC-IIIs F(x) block allows 11 breakpoints to define the input vs. output profile. The blocks are used to set up feedforward and remote setpoint signals as well as linearize relationships. For example, in combustion air flow control applications, F(x) blocks are used to “characterize” the Air Flow Demand signal to create Air Flow Controller and Oxygen Trim Controller setpoints. The example shown to the right uses separate F(x) blocks to “characterize” different setpoints for gas and oil firing. The PCC-III has the capacity to use as many F(x) functions as are required by the application.

“Learn Mode”: The PCC-III “Learn Mode” feature allows multiple F(x) block input vs. output profiles to be entered simultaneously with a push of a button! During commissioning, the control technician adjusts air and fuel flows manually to establish optimal firing conditions for a particular load point. With the conditions set, the technician simply presses the “Store” button for the PCC-III to store (learn) the current firing rate, oxygen value and burner air flow rate into the appropriate F(x) blocks simultaneously. This results in considerable savings in commissioning time, as well as an optimally “characterized” process.

Boiler Efficiency Function Block: The boiler efficiency function allows real time calculation of the boiler’s efficiency with results displayed on the controller’s front panel, recorder and/or data acquisition system. Boiler efficiency is calculated using the ASME “by losses” method. This function requires inputs of flue gas temperature, combustion (ambient) air temperature, percent oxygen in the flue gas, and percent firing rate to evaluate the efficiency. Not only does this function help establish “on-line” fired equipment efficiency, but it also helps one detect changes in efficiency, thereby alerting operating personnel of potential maintenance concerns before they become a problem. The results of efficiency calculations can also be used in advanced control applications.