It doesn’t matter what type of industry we are taking about; Temperature always play an important role.
Every process or product has some specific temperature at which processing should be done; otherwise product quality can alter. That’s why temperature controllers are connected with temperature driven processes.
These controllers not only shows the temperature but it holds the temperature at desired level by connecting or disconnecting the ‘heating’ or ‘cooling element’.
In this post, We will discuss:
- Industrial Temperature controllers
- Terminals of Temperature controllers
- Control Methods of Temperature controllers
- Types of Temperature controllers
- Types of Input sensors
- Output controlling methods
INDUSTRIAL TEMPERATURE CONTROLLERS
Temperature controllers are electronic devices equipped with microcontroller. These temperature controllers with the help of input temperature sensor continuously monitors the present temperature of the system. Meanwhile, Controller compares the present value with the set/target value.If there is error in between present value & set value than by connecting or disconnecting heating or cooling element, It maintains the temperature !
TERMINALS OF TEMPERATURE CONTROLLERS
Generally temperature controller’s terminal section consists of three sections.
- Power supply
- Sensor inputs
- Outputs
There are further types of input sensors & outputs.
For better understanding, Terminals of Selec TC-513 been discussed next !
It is clearly seen in an image above :
- Terminals 1,2 are supply terminals with voltage range of 90 to 270 Volts AC or DC.
- Terminals 6,7,8 are the input terminals for sensors. It all depend upon the sensor’s type that how many terminals are going to be utilized.
- Terminals 5,4,3 available for changeover relay. Relay rating is 10Amps @250V AC/30V DC.
- Terminals 10,12 SSR output. Output voltage is 12V DC @30mA
For better understanding, Heater control circuit through Selec TC-513 been discussed next !
It is clearly seen in an image below, RTD PT-100 3 wires is connected across the controller.
Since Heater is single phase 230V AC, Neutral is directly connected to heater. While phase to heater is controlled through SSR. When SSR get supply, Heater gets supply.
Controller produces supply to SSR as per according to its calculation to achieve the set temperature.
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CONTROL METHODS OF TEMPERATURE CONTROLLERS
Methods of Connecting or disconnecting the heating OR cooling element at which time; for how much time; is known as Control methods of Temperature Controllers.
Let’s understand this through an Example.
“A system which is having the target temperature value is 50°C & Present value is 30°C.
Case1
Temperature controller connects the heaters until it reaches to 50°C & than heaters get disconnected. But temperature still remains raising & final temperature reaches to 56°C.
Now temperature starts decreasing & falls to 45°C.
Again heaters get connected until it reaches to 50°C. At 50°C heaters get disconnected & final temperature reaches to 56°C. cycle repeat it self again & again.
In this set up, Temperature oscillates around the set temperature but do not able to maintain the desired temperature.
Case2
Present value is 30°C.
Controller makes the heater complete ON until 40°C after that heater get disconnected but temperature remains raising gradually.
Meanwhile after that,
Controller connects heater in pulse intervals such that on off on off on off. Desired temperature get achieved precisely & steadily which results temperature get maintained at 50°C. After achieving the target temperature, controller tries to maintain the present temperature near around the set temperature.
There are two controlling methods :
- ON OFF CONTROL
- PID CONTROL
1. ON OFF CONTROL
On Off control method is the simplest one in which controller connect the element on or off at fixed intervals around the set temperature. This controlling method oscillates around the set temperature but not able to get the stable around the target temperature. As explained in a case 1 above.
Next, Understanding the on off control through a graph !
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” Let suppose target temperature is 50°C & Heating element is connecting through temperature controller.
At the time of starting, System’s Ambient temperature is 20°C. Heating element get connected at starting which results temperature starts raising reaches to 30°C, 40°C .
At 45°C Heating element get disconnected.
But temperature still increasing gradually reaches to 50°C & than at last 60°C. At peak 60°C, Temperature starts decreasing reaches to 40°C at which heating element get connected again.
Temperature starts increasing & than again heating element get disconnected at 45°C But final temperature again reaches to 60°C. This cycles remains continue but system is not stable at target temperature of 50°C. This total control process is known as ON OFF CONTROL.
This type of control is useful where stable temperature is not required. “
2. PID CONTROL
In ON-OFF Control, System’s temperature is not stable. Temperature always fluctuates around the target temperature.
System which requires an accuracy with Temperature; cannot survive on on–off Control. PID Control is the best solution if we need a system with stable set temperature. PID control remains stand still at target temperature with a very little tolerance.
PID control is basically a combination of three controls Proportional, Integral & Derivative. For PID Control explanation, We are again taking a Graph example of heating element controlled through temperature controller.
“Let suppose target temperature is 50°C & ambient temperature is 20°C.
Proportional Control
In Proportional control, system’s temperature control works directly proportional to the error. This means heater control whether it is ON or OFF entirely depend upon the error between the target value & present value.
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At the time of starting As shown in a PID graph above, ambient temperature is 20°C . The difference between target temperature & present temperature is 30°C.
Heater will get directly up to 40°C . But as present temperature reaches towards the target temperature, Error value geos on decreasing. Which further get difficult to achieve the target temperature As system works proportional to the error value.
Which results present temperature will remain lower than the target value in proportional control.
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In an image shown above, Shows the Proportional band having a value in degree Celsius which is 10°C by default. System target value is 50°C than range becomes 40°C to 60°C As ±10°C of 50°C.
Proportional control works directly up to 40°C if raising from low to high White it works directly up to 60°C if falling from high to low. After Proportional control, Integral Control Starts working.
Integral Control
After Proportional band in which present value left behind the target value, Integral control come into the action.
Integral control works cumulatively to raise the temperature. While doing so integral control results in overshoot & present temperature crosses the target temperature.
In controller manual image above, Integral control has time value(minutes)(default Integral time is 2minutes in manual). If long time been selected than system overshoot less while if less time been selected than system overshoot more as it try to achieve the temperature more rapidly. This value of integral control all depend upon the type of process.
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Derivative Control
Derivative control is exact opposite of integral control which attempts to minimize the overshoot by slowing the correction factor applied As the target is approached. (Default derivative time is 30sec. in manual) “
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TYPES OF TEMPERATURE CONTROLLER
Temperature controller can be classified on the basis of two Parameters.
- BASIS OF CONTROL
- BASIS OF PROCESS
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BASIS OF CONTROL
- ON OFF control
- PID control
BASIS OF PROCESS
- Heating Temperature controllers
These temperature controllers are specially designed for heating processes. Electrical heaters are connected as a load in heating temperature controllers. OR in some cases these controllers controls the line of heating means such as steam line through controlling the valve.
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- Cooling Temperature controllers
These temperature controllers are specially designed for cooling processes. Compressors/Chiller units are connected as a load in cooling temperature controllers.
- Process controllers (Heating + Cooling)
Process controllers are the combinations of heating & cooling processes. These controllers manages the temperature at particular level by connecting or disconnecting heating or cooling element.
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TYPES OF INPUT TEMPERATURE SENSORS
Digital temperature devices can’t measure the temperature directly instead these devices observe electrical signals provided by temperature sensors.
For digital Temperature meters, There are two types of temperature sensors ‘THERMOCOUPLES’ & ‘RTD’. Both the sensors work on different working principles. These sensors provide signal to temperature controller as per change in temperature. In return controller shows the temperature As per stored information.
Thermocouples
Thermocouples are junction of two dissimilar metals which produces milli-volt change as per change in temperature. Thermocouples are two wired sensors with wide temperature range from -199°C to +1700°C. Thermocouples further have multiple types J,K,T,R&S & further these types have different temperature ranges.
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RTD
‘RTD’ stands for Resistance Temperature Detector. RTD contains a metal whose resistance value changes as per change in temperature. This resistance value of RTD continuously monitored by temperature controller. RTD are available in 2 wires, 3wires & 4 wires.
RTD temperature ranges from -50 to 400ºC. Best things about RTD is; RTD are accurate than thermocouples.
If you are curious to know why do RTD are more accurate than thermocouples, Do a comment !
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OUTPUT CONROLLING METHODS OF TEMPERATURE CONTROLLER
ELECTROMAGNETIC RELAY
Electromagnetic relay is a type of electro-mechanical element which contains an electromagnet, Electrical contacts & mechanical spring mechanism.
When electromagnet get energized common contact get connected with NO contact. When electromagnet get de-energized common contact get connected back with NC contact again due to the spring tension.
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Digital Output for SSR(Solid State Relay)
In digital output DC voltage produced by controller is used to control the SSR.
Electromagnetic relay contains mechanical moving contacts while SSR contains electronic components without any moving contact.
SSR mainly contains three terminals electronic component in which 2 terminals are input & output; While 3rd terminal act as a signal terminal. When supply get applied on 3rd terminal than input & output get connected.
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Analog Output
This output is more precises & more accurate than other types of outputs. In this method of output, Controller produces milli amps signal to control the line valves.
SUMMARY
- Temperature controllers are electronic devices equipped with microcontroller. With the help of input temperature sensor, It continuously monitors the present temperature of the system.
- By connecting or disconnecting heating or cooling element, Temperature controllers try to achieve the set temperature.
- Generally temperature controller’s terminal section consists of power supply, sensor inputs & Outputs.
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There are two controlling methods 1. ON OFF CONTROL 2. PID CONTROL
- On Off control method is the simplest one in which controller connect the element ON Or OFF at fixed intervals around the set temperature.
- PID control is a combination of three controls proportional, Integral & derivative. PID controls works in pulsating method of connecting heating or cooling element.
- Temperature controllers are categorized on two criterion : Basis of control & Basis of process.
- There are two types of temperature sensors ‘THERMOCOUPLES’ & ‘RTD’
- There are three types of output methods from the temperature controller; that are Relay output, Digital output, Analog output.
Hope, Post is beneficial. If you have any doubt, Suggestion or query Please do comments !