Boiler controllers monitor and maintain variables such as steam temperature and pressure in order to control a boiler’s burner or air mixture. They differ in terms of functionality, user interface, and form factor. Choices for boiler control functionality include: rate indication or control, totalizing, data logging, and chart recording. In terms of the user interface, boiler controllers may include a digital front panel or analog components such as knobs and switches. Computer-programmable, web-enabled, and network-ready boiler controls are commonly available. There are several form factors for boiler controllers. Some products are printed circuit boards (PCB). Others are designed for mounting in a rack, on a DIN rail, or on a wall, chassis, or cabinet enclosure. Stand-alone boiler controllers are benchtop or floor-standing units with a full-casing or cabinet and an integral interface.
Specifications for boiler controllers include number of inputs, number of outputs, input types, output types, and number of zones (if applicable). The number of inputs equals the total number of signals sent to the boiler controller. The number of outputs equals the total number of outputs used to control, compensate or correct the process. Input types for boiler controllers include: direct current (DC) voltages, current loops, analog signals from resistors or potentiometers, frequency inputs, and switch or relay inputs. Output types include analog voltages, current loops, switch or relay outputs, and pulses or frequencies. Boiler controllers can also send inputs or receive outputs in serial, parallel, Ethernet or other digital formats which indicate a process variable. Some boiler controllers can send or receive accept commands and inputs from information converted to an industrial fieldbus protocol such as CANbus, PROFIBUS®, or SERCOS. PROFIBUS is a registered trademark of PROFIBUS International.
Boiler controllers differ in terms of control techniques. Limit control establishes set points or limits that, when reached send a signal to stop or start a process variable. This off-on or bang-bang control is a fairly simple type of control. Linear control matches a variable input signal with a correspondingly variable control signal. Signal conditioning, filtering, and amplification can be used to produce the proper output control signal. Proportional, integral, and derivative (PID) control requires real-time system feedback. Feedforward control provides direct-control compensation from the reference signal. It may be open-loop or used in conjunction with more advanced PID control. Fuzzy logic is a type of control in which variables can have imprecise values (as in partial truth) rather than a binary status (completely true or completely false). Advanced or nonlinear controls include algorithms such as neural networking and adaptive gain.
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Environmental controllers control environmental factors such as temperature, humidity, and air pressure. The environment to control can be an office or workspace, or inside a chamber for testing or process purposes.
Flow controllers monitor and maintain flow-rate variables, typically in process applications.
Furnace controllers are used to control temperature, heat delivery, and other variables in industrial furnaces. They control the burner flame, air mixture and trim to maintain and optimize furnace performance.
HVAC controllers are used to monitor and control heating, ventilation and air conditioning (HVAC) systems in buildings. They monitor indoor environmental factors such as temperature and humidity, and control heating and cooling to maintain desired levels.
Pressure controllers accept input from pressure sensors, transmitters, gauges, and other devices and subsequently control adjustment to the pressure to maintain or achieve the desired pressure level.
Pump controllers monitor flow and/or level variables, and control a pump accordingly to maintain the desired levels. Pump control can include simply turning a pump on and off, or more advanced controls for pump speed, output pressure, etc.
Purge Controllers and Indicators
Purge controllers and purge indicators are used to regulate and monitor hazardous environments within enclosures.
Specialty Process Controllers
Specialty industrial process controllers are used in unlisted, specialized or proprietary applications.
Temperature controllers accept inputs from temperature sensors or thermometers, and then output a control signal to keep the temperature at the desired level.