PCC-IV Instruction Manual (rev. 0.1)
Page 1-5
Section 1 - Product Overview
Special Option Card and Special Function Block Capabilities
The following are applications features of the PCC-IV which extend its capabilities considerably:
Multiple F(x)
The F(x) function-type
allows for “characterizing” or “curve fitting” of a relationship when that relationship is non-
linear. In combustion control applications, as an example, it is desirable to have the fuel input to a burner follow a
linear relation with firing rate demand. Even with a properly selected valve trim, the relationship will not be perfectly
linear, but with the application of an F(x) block, this objective can be realized. The PCC-IV has the capacity to use
as many F(x) functions as are required by the application.
Learn Mode
The learn mode allows for easy commissioning of applications involving single or multiple non-linear functions. This
capability is best described with an example. In combustion control applications, as the firing rate is increased, the
best combustion air damper position will likely not be a linear function. An F(x) block can be used to effectively
linearize the combustion air flow vs. firing rate relationship. F(x) blocks will likely be required for the fuel-valve-
degree-of-opening demand signal and the oxygen setpoint (if O
2
Trim is provided). The clear benefit of the learn
mode is that at each of the F(x) block data points, after optimum conditions are set by the technician, he/she simply
presses the “Learn” button for the PCC-IV to remember (learn) the current firing rate vs. valve and damper positions
and oxygen setpoint relationships simultaneously. The technician then proceeds in a similar fashion up to full firing
rate, repeating this procedure at each point. This results in a considerable savings in commissioning time and an
optimally characterized process.
Boiler Efficiency
The boiler e
fficiency function allows the controller to calculate, in real time, the boiler’s efficiency and display that
resul
t on the controller’s front panel (and/or a recorder or a Data Acquisition terminal). Boiler efficiency is calculated
usin
g 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 (for radiation loss determination) to evaluate
the efficiency. This function is not only useful for establishing on-line fired equipment efficiency, but also allows
determination of changes in that efficiency and therefore the potential for maintenance.
Triac Output for Electric Actuators (option cards)
Many systems utilize electric actuators where a bi-directional on-off voltage signal is used to drive the actuator open
or closed. The PCC-IV has the optional interface electronics to accomplish this control action. Additionally, the Triac
Output option card(s) include position feedback input provisions for optimizing control of actuator position.
Service Manual and Block Forcing
In Service Manual mode, controller 4-20mA outputs and/or servo Triac Outputs can be manually controlled from
the faceplate, and the associated logic is overridden. Individual outputs, or all outputs can be placed in Service
Manual mode. Service Manual is useful for initial process or burner setup and to manually operate a unit in the
event a critical sensor, transmitter, or wiring fault occurs.
With a password, any block output can be forced to any value. This is useful for technician-level debugging and
operation until a transmitter is repaired/replaced.
Steam Flow Pressure Compensation
Accurate steam flow measurements are very important to the control and monitoring of process systems. Even
though most control systems are designed to assure a constant pressure, variations and/or upsets can occur, which,
if unaccounted for, can render records erroneous and produce unacceptable instabilities in all control loops upon
which this measurement depends.
Gas Flow Pressure/Temperature Compensation
Most gas flow measurements require some level of pressure and/or temperature compensation. This becomes
important
when the flow measurement is a significant process control variable as it is in a “fully metered” combustion
control strategy.
High-Temperature Hot-Water (HTHW) BTU/Hr Computation
An important characteristic of any high-temperature, hot-water g
enerator is the quantity of BTU’s produced per
interval of time.
With inputs of the generator’s inlet and outlet water temperatures and the water’s flow rate, this
value can be easily calculated. The resultant value is typically compared to that from the boiler efficiency calculation
to determine if possible problems have arisen.
