Temperature and process controllers are used over a vast range of industrial, scientific and commercial applications. These controllers automatically adjust outputs based on sensor feedback working in concert to control process variables such as temperature, flow, pressure and relative humidity, as well as, to achieve an optimized and stable process.
Temperature Control in manufacturing is a quintessential part of proper product formation. If the temperature slips above or below the ideal range needed for a particular stage in a manufacturing process, the results can be harmful—improperly adhered coatings, a weakened base material, or an overall compromised component—so it becomes increasingly important that the manufacturer not only determine the proper temperature for each stage, but also monitor the temperature inside the machine and receive appropriate feedback.
Temperature controllers in manufacturing operations serve exactly this function: they ensure that a machine is running properly by gauging the temperature at different stages in the process and comparing the data to the programmed temperature specifications. As a result, manufacturers can quickly and easily discover temperature related machine malfunctions, and treat them as necessary.
A temperature controller is a device used to hold a desired temperature at a specified value.
In a typical application, sensors measure the actual temperature. This sensed temperature is constantly compared to a user set point. When the actual temperature deviates from the set point, the controller generates an output signal to activate other temperature regulating devices such as heating elements or refrigeration components to bring the temperature back to the set point.
Temperature controllers have inputs. The inputs are used to measure a variable in the process being controlled. In the case of a temperature controller, the measured variable is temperature.
In addition to inputs, a temperature controller also has an output. Each output can be used to do several things including control a process (such as turning on a heating or cooling source), initiate an alarm, safe guard a process with a HI or LOW Limit shutdown or to retransmit the process value to a programmable logic controller (PLC) or recorder.
Limit controllers provide safety limit control over process temperature. They have no ability to control temperature on their own. Put simply, limit controllers are independent safety devices to be used alongside an existing control loop. They are capable of accepting thermocouple, RTD, or process inputs with limits set for high or low temperature just like a regular controller. Limit control is latching and part of redundant control circuitry to positively shut a thermal system down in case of an over-limit condition. The latching limit output must be reset by an operator; it will not reset by itself once the limit condition does not exist. A typical example would be a safety shut off for a furnace. If the furnace exceeds some set temperature, the limit device would shut the system down. This is to prevent damage to the furnace and possibly any product that may be damaged by excessive temperatures. Or to Prevent dangerous situations like explosions or fires.
On/Off Temperature Controls
An on/off temperature control is the least expensive of the control types, and also the most simple in terms of how it works. The control is either on or off—if the temperature drops below a certain point, the control signals to the machine to turn raise the temperature. Likewise, if a temperature goes above a certain point, the control is triggered to tell the machine to lower the temperature. A common example of on/off systems is a household thermostat. When the temperature drops below a certain point, the controller triggers the heater to raise the temperature back to the programmed value. With air-conditioning it works the other way: if the temperature rises past a certain point, the controller triggers the air-conditioner, dropping the temperature back to the programmed norm.
On/off controls are often used in processes where the temperature change is very slow, and precise control of temperature isn’t necessary.
Proportional Control
Unlike on/off controls, which only respond when a set limit is reached, proportional controls are designed to respond to temperature change before it slips out of the desired range. Essentially, proportional controls increase or decrease the power supply as the temperature reaches its upper or lower limit, or setpoint, which slows or speeds the heater and helps stabilize the temperature.
The temperature range in which proportional controls either lessen or increase the power supply to slow or speed heating is known as the “proportional band.” If a temperature reaches the lower or upper setpoints, the control then functions as a full on/off control—the temperature is either turned fully on to increase the temperature, or fully off to drop the temperature. When the temperature is within the proportional band, and the power supply is decreased or increased, the heat is raised or lowered in relation to how far the temperature is from the set point. 
Another temperature loop involves taking a shower. The person taking he shower becomes the sensor and adjusts the temperature of the water based on its hotness or coldness against the skin and mixing the hot and cold water from the spigot. Other temperature loops are hot water tanks, tankless water heaters, ovens and cars/trucks (engine cooling and cabin temperature regulation (AC or heat).
In industry, more sophisticated means are needed as more precise temperature control is needs. Thus the rise of the Process Temperature controller. Using PID control and very small time intervals, Process controllers can control to tenths of degrees by switching electric heaters on or off in microseconds or by adjusting voltages to control wattage output (like a dimmer switch.)
We can help size a thermal system with the right heater, sensor type and placement and temperature controller. Contact Anderson-Bolds for expert help with process heating applications. We can definitely enhance your process.
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