Why do we need temperature control?
Temperature controllers are required in any situation where you need a stable temperature. This can be when an object or environment requires heating, cooling, or both, and remains at the desired temperature (regardless of temperature), regardless of the temperature change of the surrounding environment.
There are two basic types of temperature control. Open loop control and closed loop control. The open loop controller is a simple control mode that applies continuous heating or cooling regardless of the actual temperature output. An example of this is the control of a car’s internal heating system. On a cold day, you may need to turn on your heating system to warm up to 26 degrees Celsius. But, in hot weather, this setting makes the car much warmer than 26 degrees.
Closed loop control is much more complex than open loop control. In a closed loop program, the output temperature is continuously measured and adjusted to maintain a constant output at optimum temperature. Closed loop control is always aware of the output signal and communicates it to the controller. An example of closed-loop control is the car’s smart thermometer with indoor temperature controller. For example, if you set the car temperature to 26 degrees Celsius, Smart Control automatically adjusts heating (on cold days) or cooling (on hot days) to maintain the target temperature of 26 degrees.
Introduction to temperature controllers
A temperature controller is a device that holds the desired temperature in a specified amount. The simplest example of temperature control is the thermostat found in homes. For example, a hot water heater uses a thermostat to control the water temperature and maintain it at the specified temperature. Temperature controllers are also used in ovens. When the temperature is set for the oven, a controller controls the actual temperature inside the oven. If it is lower than the set temperature, it sends a signal to activate the heater to return the temperature to the standard level. Thermostats are also used in refrigerators. So if the temperature gets too high, a controller will start lowering the temperature.
Industrial Controller Programs
Industry temperature controllers work in much the same way as in home systems. A temperature controller provides control of industrial or laboratory heating and cooling processes. In a typical application, the sensors measure the actual temperature. This sensor continuously measures the temperature and compares it with the user set temperature. When the actual temperature deviates from the set point, the controller generates an output signal to activate temperature regulating devices such as heating or cooling elements and return the temperature back to the set value.
Common applications in industry
Temperature controller is used in various industries, including in the management of production processes or operations. Some of the common applications for temperature control in the industry include extrusion and injection molding machines, furnaces, packaging machines, food processing, food storage and blood banks. The following are some of the common applications of temperature control in the industry.
Heat treatment of furnaces and ovens
The temperature controller is used in the heating process of stoves and furnaces, ceramic stoves, boilers and heat exchangers.
Packaging
In the packaging world, product envelope sealing machines, adhesive machines, product packaging tunnels or industrial labelers are temperature controlled and must operate at specified temperatures and specific processing times. Temperature controllers precisely adjust these operations to ensure high quality product output.
Plastic
Temperature control in the plastics industry is common in many cases, including dryers and molding equipment and mold removal. In mold extraction equipment, temperature controllers are used for precision monitoring and temperature control at various sensitive points in plastic production.
Health care
The temperature controller is used in the healthcare industry to increase the accuracy of temperature control. Conventional equipment that uses temperature controls include laboratory equipment, laboratories, autoclaves, incubators, refrigeration equipment, and also the test rooms in which samples must be stored or tests must be performed on specific temperature parameters.
Food and Drink
Food processing applications include temperature control including brewing, mixing, sterilizing and cooking stoves. The controller adjusts the temperature and processing time to ensure optimum performance.
Parts of temperature control
All controllers have several common components. In the first section the controllers have inputs. Inputs are used to measure variables in the process being controlled. In the case of a temperature controller, the variable is the temperature measurement.
Inputs
Temperature controllers can have several types of inputs. The type of input sensor and signal required may vary depending on the process being controlled. Typical input sensors include thermocouples and resistive sensors (RTD) and linear inputs such as mV and mA. Standardized thermocouple types include J, K, T, R, S, B and L.
Controllers can also be set to accept RTD as a temperature sensor input. A typical RTD of a platinum sensor is usually 100 ohms.
On the other hand, controllers can be adjusted to receive voltage or current signals in millivolts, volts, or mAps, as with other sensors such as pressure, level or current sensors. Typical input voltage signals include 0 to 5VDC, 1 to 5VDC, 0 to 10VDC and 2 to 10VDC. Controllers may also be tuned to receive millivolts from sensors containing 0 to 50mVDC and 10 to 50mVDC. Controllers can also accept mA signals such as 0 to 20mA or 4 to 20mA.
A controller typically has an important feature to detect temperature input when the input is faulty or interrupted. This is known as a crash detector. This error can cause significant damage to the controller equipment. This feature enables the controller to stop the process if the sensor failure conditions are observed.
Outputs
In addition to the inputs, each controller has output. Each output can be used to perform several tasks, including controlling a process (such as turning on a heating or cooling source), initiating an alarm, or relocating the process value to a Programmable Controller (PLC) or register.
Typical outputs that have a temperature controller include relay output, electronic relay driver (SSR), analog and linear outputs.
The relay output is usually a single-polarized relay (SPDT) with a DC voltage coil. The controller transmits current to the relay coil and provides connection separation. This allows the connector controller to control an output voltage source to supply the coil power of a larger contactor. Note that the connection relay current is usually less than 2 amps. This connector can control a contactor heating connection with a current of 10-20 amps used by steam or heating elements.
Another type of output is the SSR driver. SSR driver outputs are logic outputs that turn on or off an electronic relay. You need 3 to 32VDC to clear more relays. A typical 10V SSR driver lighting signal can control three electronic relays.
Triac provides relay performance without any extra parts. These SSR relays control currents up to 10 A. Triac outputs may have a small amount of leakage deviation, usually less than 50 mA. This leakage current does not affect the heating contactor circuits, but may be a problem if the output is used to connect to another electronic circuit such as the PLC input. If you are concerned, the standard relay connection would be a better choice. This current provides absolute zero when the output is switched off and the connection is open.
Analog outputs are available on some controllers that provide 0-10V or 4-20mA signal. These signals are calibrated so that the signal changes as a percentage of output. For example, if a controller sends a 0% signal, the analog output will be 0 volts or 4 mA. When the controller sends a 50% signal, the output will be 5V or 12 mA. When the controller sends a 100% signal, the output will be 10 volts or 20 mA.
Other parameters
Temperature controllers have several other parameters, one of which is the setting point. In essence, it is a set point and a target set by an operator whose controller intends to remain constant. For example, a temperature setting of 30 degrees Celsius means that the purpose of the controller is to keep the temperature at this value.
Another parameter is the alert value. This is used to indicate when a particular condition will be reached. There are many variations in the types of alarms. For example, a loud alarm can indicate that the temperature is warmer than some values. Likewise, a low-level alarm indicates that the temperature has fallen below a set temperature.
For example, in a temperature control system, a constant alarm to prevent damage to heating equipment by switching off the source is to prevent damage to the equipment when the temperature rises above a certain value. On the other hand, the alarm may be low and low temperatures can damage the equipment by freezing.
The controller can also test a broken output device such as an open heating element by examining the output signal level and comparing it with the modified input signal level. For example, if the output signal is 100% and the input sensor does not detect the temperature change after a specified time, the controller determines that the loop is broken. This feature is known as Loop Alarm.
Another type of diversion alarm is. This numeric value is set more or less than the point. Deviation alarms control the process designation point. The operator will be notified when the pre-programmed changeover process starts from the set point. This alarm range operates on or off the set temperature band. Typically, these warning points are slightly higher and slightly below the controller setpoint.
For example, if the setting is 150 degrees and the deflection alarms are set at 10 degrees, the alarm is activated when the temperature reaches 160 degrees at the upper end or 140 degrees at the lower end. If the setpoint is changed to 170 degrees, the alarm is activated at 180 degrees and the bottom alarm at 160 degrees.
Another common set of parameters is the PID parameter controller. PID, acronym, integral, derivative, is an advanced control function that uses feedback from a controlled process to determine the best way to control that process.
How does the controller work?
All controllers, from the simplest to the most complex, work in almost one way. Controllers control or hold some variables or parameters in a specified value. There are two variables required by the controller. The actual input signal and the desired point value. The input signal is also known as the amount of processing. Depending on the controller, the input to the controller is sampled multiple times per second.
This input value or process is compared to the set value. If the actual value does not match the set point, the controller generates an output signal based on the difference between the set point and the processing value and whether the processing value approaches or exceeds the specified range. This output signal then initiates a response to correct the actual value to match the set point. Usually, the control algorithm updates the amount of output power applied to the output.
The control function performed depends on the type of controller. For example, if the controller is an on / off controller, the controller decides whether to turn the output on or off or release it to its current state.
On / Off control is one of the simplest types of controls to implement. Works with setting up a hysterical band. For example, a temperature controller may be set to control room temperature. If the set point is 68 degrees and the actual temperature drops to 67 degrees, an error signal indicates a -1 degree difference. The controller then sends the signal to increase the applied heat to bring it back to 68 degrees. When the temperature reaches 68 degrees, the heater turns off. For temperatures between 68 and 67 degrees, the controller does nothing and the heater stays off. However, when the temperature reaches 67 degrees, the heater re-enters the system.
Unlike the ON / OFF control, the PID control determines the exact amount of output needed to maintain the optimum temperature. Output power can range from 0 to 100%. When using an analog output type, the output drive is proportional to the amount of output power. But if the output is a binary output type, such as a relay, SSR or triac driver, the output must be proportional to achieve the analog profile.
A time-proportional system uses a time-cycle to adjust the output value. If the cycle time is set to 8 seconds, the system that consumes 50% power will turn off the output for 4 seconds and for 4 seconds. Until the power value changes, the time values do not change. Over time, on average 50% of the amount given is half and half off. If you need 25% output power, at the same time for 8 second cycles, the output will be off for 2 seconds and off for 6 seconds.
If everything is equal, shorter time is desirable because the controller can respond faster and change the output state for certain changes in the process. According to relay mechanics, shorter cycle times can shorten the life of a relay and are not recommended to be less than 8 seconds. For high-end electronic devices such as SSR or triac drivers, faster switching times are better. Longer switching times, regardless of the type of output, allow for greater fluctuation in process value. The general rule is that, only if the process allows, when the relay output is used, the cycle time is longer.
Additional features
Controllers can also have a number of optional extra features. One of them is the ability to communicate. A communication link allows the controller to communicate with a PLC or a computer. This feature allows data exchange between the controller and the host. An example of a regular data exchange could be a host computer or a PLC that reads the process value.
The second option is a remote setting. This feature allows a remote device such as a PLC or PC to change the controller point. However, unlike the above mentioned communication capability, the remote input uses a linear analog input signal that is proportional to the setpoint value. This will give the operator more flexibility to remotely change the setting value. A typical signal may be 4-20 mA or 0-10 volts direct.
Another common feature used in controllers is the ability to configure them using special software on PCs that is established via a device communication link, allowing the controller to quickly and easily configure and save settings for use. Be provided next.
Another common feature is digital input. The digital input can work in conjunction with a remote set point for local selection or a remote for the controller. It can also be used to select between setpoint 1 and setpoint 2 as planned in the controller. Digital inputs can also be reset remotely if you enter limited conditions.
Other optional features include the transmitter power supply, which is used to power the 20-20 mA sensor. This power supply is used to supply 24V direct current with a maximum of 40 mA.
In some applications, the dual-color display can also be a desirable feature and will help to identify different controller states. Some products also have displays that change from red to green or vice versa depending on pre-programmed conditions, such as an alarm display. In this case, no alarm may be displayed with the green display, but if the alarm is present, the display will turn red.
Types of controllers
Temperature controllers come in a variety of styles with a wide range of features and capabilities. There are also many ways to classify controllers according to their functional capabilities. Generally, temperature controllers are either single-loop or multi-loop. Single-loop controllers have one input and one or more outputs to control a thermal system. On the other hand, multi-loop controllers have different inputs and outputs and are able to control multiple loops in one process. More control loops allow more process control over system functions.
Single-loop controllers range from simple devices that can only manually change settings to complex devices that can automatically make up to eight adjustments in a given time period.
Analog models
The simplest, most basic type of controller is the analog controller. Analog controllers are low-cost and simple to use for simple and reliable process control in harsh industrial environments, such as those with significant electrical noise and noise. The controller display is usually a button.
Analog controllers are often used in non-critical or simple heating systems to provide simple ON-OFF temperature control for direct or reverse operation applications. The controllers accept thermocouple or RTD inputs and offer optional percentage control mode for systems without temperature sensors. Their main drawbacks are the lack of readable screens and the lack of professional capabilities for more challenging control tasks. In addition, the lack of any communication power limits their use to simple applications such as switching on / off heating elements or cooling devices.
Switches (range control)
These controllers provide the control range in the temperature measurement process. They are not capable of controlling temperature alone. Simply put, restricted controllers are standalone safety devices that can be used alongside an existing control loop. They are capable of accepting thermocouples, RTDs, or processing inputs with set limits for high or low temperatures just like a conventional controller. Limited control is in series in the circuit and is part of the control circuit that turns off a system in case of excessive conditions. The output must be reset by an operator. When there is no restriction requirement, it will not reset on its own. An obvious example is the safety shutdown for the furnace. If the oven exceeds the set temperature, the machine turns off the system’s permissible limit. This will prevent damage to the furnace and possibly any product that may be damaged by overheating.
Multifunction temperature controllers
General purpose temperature controllers are used to control the most common processes in the industry. Typically, they come in a range of standard sizes, with multiple outputs and programmable output functions. These controllers can also perform excellent PID control for overall control situations. They are in the front panel for easy access by operators.
Most modern digital temperature controllers can calculate PID parameters for optimal thermal system performance using automated tuning algorithms. These controllers use a preset function to calculate PID parameters for a process and a continuous adjustment function to continuously modify PID parameters. This enables quick adjustment, saving time and reducing waste.
Specifications
Advanced temperature control devices have different specifications and parameters. These specifications are as follows in TamKar Engineering’s temperature control products:
- Capability measuring by NTC and PT100 sensors
- Capability measuring by thermocouple sensors(J,K,S,R)
- Temperature accuracy 0.1 ‘C
- Two separate temperature control outputs
- Heating and Cooling control
- Defrost timer for fridge systems
- ON-OFF output control by adjustable hysteresis
- Two separate output for temperature control and alarm
- Software calibration access
- Open and Short sensor connection alarm
- Voltage range 180-240 VAC
Other features of temperature controller
Power supply voltage
There are usually two power supply voltage options when controlling the temperature: low voltage (24VAC / DC) and high voltage (110-230VAC).
Size
Controllers come in a variety of standard sizes that are indicated by DIN numbers such as 1/4 DIN, 1/8 DIN, 1/16 DIN and 1/32 DIN. DIN is the abbreviation for “Deutsche Institut fur Normung”, a German standardization and measurement organization. For our purposes, DIN simply indicates that a device complies with a generally accepted standard for panel dimensions.
The smallest size is DIN 32/32, which is 48 mm x 48 mm, and a corresponding panel is 22.5 x 45.5 mm. The next size is DIN 1/16, measuring 48mm by 48mm with a 45mm x 45mm panel size. DIN 1/8 with a board thickness of 92 mm 48 96 mm 48 96 mm. Finally, the largest 1/4 DIN size is 96 × 96mm with a 92mm 92mm panel cutout.
It is important to note that DIN standards do not specify how deep a controller is behind the panel. The standards only allow for front panel dimensions and panel cutting dimensions.
Standard Approvals
It is desirable that a temperature controller have some type of agency approval to ensure that the controller meets minimum safety standards. The type of approval depends on the country where the controller will be used. The most common approvals, UL and CUL registration, are for all controllers used in the United States and Canada. Usually a certificate is required for each country.
For controllers used in EU countries, CE approval is required.
The third type is FM approval. This applies only to restricted devices and to controllers in the United States and Canada.
Front panel rating
An important feature of the controller is the front panel housing rating. These ratings can be either an IP rating or a NEMA rating. IP ratings (Ingress Protection) apply to all controllers and are usually IP65 or higher. This means that only the front panel, the controller is completely protected from dust and low-pressure atmospheres in any direction, and only limited entry is permitted. IP ratings are used in the US, Canada and Europe.
The rating of a NEMA (National Association of Electrical Manufacturers) controller coincides with the IP rating. Most controllers are NEMA 4 or 4X grade, meaning they can be used in applications that only need water (not oil or other solvents). X in the NEMA 4X rating means that the front panel is not corroded. NEMA ratings are primarily used in the United States and Canada.
