How To Do Decoupling In Temperature Control

Temperature Controller Nuts Handbook

Courtesy of Danaher Industrial Controls Grouping - Procedure Automation, Measurement, & Sensing
Run into all of Danaher'due south Partlow and Westward Controllers

Why practice we demand temperature controllers?

Temperature controllers are needed in any situation requiring a given temperature exist kept stable. This can be in a situation where an object is required to be heated, cooled or both and to remain at the target temperature (setpoint), regardless of the changing environment around it. There are 2 fundamental types of temperature control; open loop and closed loop control. Open up loop is the most basic course and applies continuous heating/cooling with no regard for the actual temperature output. It is analogous to the internal heating organization in a car. On a cold solar day, yous may need to plow the rut on to full to warm the car to 75°. All the same, during warmer weather, the same setting would get out the inside of the car much warmer than the desired 75°.

Open loop control block diagram

Closed loop command is far more sophisticated than open loop. In a closed loop application, the output temperature is constantly measured and adjusted to maintain a constant output at the desired temperature. Closed loop control is always conscious of the output signal and will feed this back into the command process. Closed loop command is analogous to a car with internal climate command. If you lot set the car temperature to 75°, the climate control will automatically accommodate the heating (during cold days) or cooling (during warm days) equally required to maintain the target temperature of 75°.

Closed loop control block diagram

Introduction to Temperature Controllers

A temperature controller is a device used to agree a desired temperature at a specified value.

The simplest example of a temperature controller is a mutual thermostat found in homes. For instance, a hot water heater uses a thermostat to control the temperature of the h2o and maintain information technology at a sure commanded temperature. Temperature controllers are also used in ovens. When a temperature is set for an oven, a controller monitors the bodily temperature inside of the oven. If it falls below the fix temperature, information technology sends a signal to activate the heater to raise the temperature dorsum to the setpoint. Thermostats are likewise used in refrigerators. And then if the temperature gets too high, a controller initiates an action to bring the temperature down.

Common Controller Applications

Temperature controllers in industry work much the same way they do in common household applications. A basic temperature controller provides control of industrial or laboratory heating and cooling processes. In a typical application, sensors measure the actual temperature. This sensed temperature is constantly compared to a user setpoint. When the actual temperature deviates from the setpoint, the controller generates an output betoken to activate other temperature regulating devices such as heating elements or refrigeration components to bring the temperature dorsum to the setpoint.

Common Uses in Industry

Temperature controllers are used in a wide multifariousness of industries to manage manufacturing processes or operations. Some common uses for temperature controllers in manufacture include plastic extrusion and injection molding machines, thermo-forming machines, packaging machines, food processing, food storage, and claret banks. The following is a brief overview of some common temperature control applications in industry:

Heat Care for/Oven
Temperature controllers are used in ovens and in heat-treating applications within furnaces, ceramic kilns, boilers, and heat exchangers.
Packaging
In the packaging world, machinery equipped with seal bars, mucilage applicators, hot melt functions, compress wrap tunnels or label applicators must operate at designated temperatures and process time lengths. Temperature controllers precisely regulate these operations to ensure a high quality product output.
Plastics
Temperature control in the plastics industry is common on portable chillers, hoppers and dryers and molding and extruding equipment. In extruding equipment, temperature controllers are used to precisely monitor and control temperatures at different critical points in the production of plastic.
Healthcare
Temperature controllers are used in the healthcare industry to increase the accuracy of temperature control. Common equipment using temperature controllers includes laboratory and test equipment, autoclaves, incubators, refrigeration equipment, and crystallization growing chambers and exam chambers where specimens must be kept or tests must be run within specific temperature parameters.
Food & Beverage
Common nutrient processing applications involving temperature controllers include brewing, blending, sterilization, and cooking and baking ovens. Controllers regulate temperature and/or procedure time to ensure optimum performance.

Parts of a Temperature Controller

All controllers have several common parts. For starters, controllers have inputs. The inputs are used to measure out a variable in the process being controlled. In the example of a temperature controller, the measured variable is temperature.

Inputs

Temperature controllers can have several types of inputs. The type of input sensor and signal needed may vary depending on the type of controlled process. Typical input sensors include thermocouples and resistive thermal devices (RTD's), and linear inputs such as mV and mA. Typical standardized thermocouple types include J, K, T, R, S, B and 50 types amid others.

Controllers can besides exist set to accept an RTD as a temperature sensing input. A typical RTD would be a 100Ω platinum sensor.

Alternatively, controllers tin can exist set to accept voltage or current signals in the millivolt, volt, or milliamp range from other types of sensors such as force per unit area, level, or flow sensors. Typical input voltage signals include 0 to 5VDC, one to 5VDC, 0 to 10VDC and 2 to 10VDC. Controllers may also be set up to accept millivolt signals from sensors that include 0 to 50mVDC and 10 to 50mVDC. Controllers can also accept milliamp signals such equally 0 to 20mA or 4 to 20mA.

A controller will typically incorporate a characteristic to detect when an input sensor is faulty or absent-minded. This is known as a sensor interruption detect. Undetected, this fault condition could cause significant impairment to the equipment being controlled. This characteristic enables the controller to cease the process immediately if a sensor pause status is detected.

Outputs

In improver to inputs, every controller too has an output. Each output can exist used to do several things including control a process (such as turning on a heating or cooling source), initiate an warning, or to retransmit the process value to a programmable logic controller (PLC) or recorder.

Typical outputs provided with temperature controllers include relay outputs, solid land relay (SSR) drivers, triac, and linear analog outputs. A relay output is ordinarily a single-pole double-throw (SPDT) relay with a DC voltage coil. The controller energizes the relay coil, providing isolation for the contacts. This lets the contacts control an external voltage source to power the coil of a much larger heating contactor. It's of import to annotation that the electric current rating of the relay contacts is usually less than 2A. The contacts can control a heating contactor with a rating of ten–20A used by the heater bands or heating elements.

Another type of output is an SSR driver. SSR commuter outputs are logic outputs that turn a solid-country relay on or off. Nigh solid-country relays require three to 32VDC to turn on. A typical SSR driver plow-on signal of 10V can drive three solid-state relays.

A triac provides the relay part without any moving parts. Information technology is a solid country device that controls currents up to 1A. Triac outputs may permit some pocket-size amount of bleed current, ordinarily less than 50mA. This drain electric current doesn't impact heating contactor circuits, but information technology may be a problem if the output is used to connect to some other solid-state excursion such equally a PLC input. If this is a concern, a standard relay contact would be a better choice. It provides absolute cipher current when the output is de-energized and the contacts are open.

Analog outputs are provided on some controllers which put out a 0–10V signal or a 4–20mA signal. These signals are calibrated then that the signal changes every bit a percent of the output. For example, if a controller is sending a 0% signal, the analog output volition be 0V or 4mA. When the controller is sending a 50% signal, the output will be 5V or 12mA. When the controller is sending a 100% bespeak, the output will exist 10V or 20mA.

Other Parameters

Controller alarm comparison

Temperature controllers accept several other parameters, one of which is a setpoint. Basically, a setpoint is a target value set past an operator which the controller aims at keeping steady. For instance, a setpoint temperature of xxx°C ways that a controller will aim to keep the temperature at this value.

Another parameter is an alarm value. This is used to betoken when a process has reached some given condition. There are several variations on types of alarms. For instance, a high alarm may indicate that a temperature has gotten hotter than some set value. Likewise, a low alarm indicates the temperature has dropped below some set value.

For example, in a temperature control system, a high fixed alarm prevents a estrus source from damaging equipment by de-energizing the source if the temperature exceeds some setpoint value. A depression stock-still alarm, on the other hand, may be set if a low temperature could damage equipment by freezing.

The controller can also exam for a broken output device, such as an open heating element, by checking the corporeality of output point and comparing it to the amount of detected change in the input signal. For example, if the output point is 100% and the input sensor does not find any modify in temperature after a certain time period, the controller volition decide that the loop is broken. This feature is known as Loop Alert.

Another blazon of alarm is a deviation alarm. This is set up at some plus-or-minus value from the setpoint. The difference alarm monitors the process setpoint. The operator is notified when the process begins to vary some preprogrammed amount from the setpoint. A variation on the deviation warning is the band alarm. This warning will activate either inside or outside a designated temperature band. Typically, the alert points are half above and half below the controller setpoint.

For example, if the setpoint is 150° and the deviation alarms are set at ±x°, the alarms would be activated when the temperature reached 160° at the high end or 140° at the depression end. If the setpoint is changed to 170°, the high alarm would actuate at 180° and the low alarm at 160°. Another common set of controller parameters are PID parameters. PID, which stands for proportional, integral, derivative, is an advanced control function that uses feedback from the controlled process to decide how all-time to control that procedure.

How it Works

All controllers, from the basic to the near complex, work pretty much the same way. Controllers control, or hold, some variable or parameter at a set value. There are ii variables required past the controller; bodily input betoken and desired setpoint value. The input signal is also known as the process value. The input to the controller is sampled many times per second, depending on the controller.

This input, or process, value is then compared with the setpoint value. If the actual value doesn't match the setpoint, the controller generates an output signal alter based on the difference between the setpoint and the process value and whether or not the process value is budgeted the setpoint or deviating farther from the setpoint. This output signal then initiates some blazon of response to correct the bodily value and so that it matches the setpoint. Unremarkably, the control algorithm updates the output power value which is and then applied to the output.

The control action taken depends on the blazon of controller. For instance, if the controller is an ON/OFF control, the controller decides if the output needs to be turned on, turned off, or left in its nowadays state.

ON/OFF command is ane of the simplest types of command to implement. It works past setting up a hysteresis band. For instance, a temperature controller may be fix to control the temperature inside of a room. If the setpoint is 68° and the actual temperature falls to 67°, an error signal would prove a –one° deviation. The controller would then send a indicate to increase the applied heat to raise the temperature back to the setpoint of 68°. Once the temperature reaches 68°, the heater shuts off. For a temperature between 68° and 67°, the controller takes no activity and the heater remains off. Yet, once the temperature reaches 67°, the heater will once more kick in.

Different ON/OFF control, PID control determines the verbal output value required to maintain the desired temperature. The output power tin range from 0 to 100%. When an analog output type is used, the output drive is proportional to the output power value. However, if the output is a binary output type such as a relay, SSR driver, or triac, then the output must be time proportioned to obtain an analog representation.

A time proportioned organisation uses a cycle time to proportion the output value. If the cycle time is set to 8 seconds, a system calling for 50% power will have the output on for four seconds and off for 4 seconds. Every bit long equally the power value doesn't change, the time values wouldn't change. Over time, the power is averaged to the 50% allowable value, half on and half off. If the output ability needed to be 25%, then for the same viii second cycle time, the output would be on for 2 seconds and off for half-dozen seconds.

Output time proportioning case

All things beingness equal, a shorter cycle time is desirable considering the controller can more speedily react and modify the state of the output for given changes on the process. Due to the mechanics of a relay, a shorter wheel time can shorten the life of a relay, and is not recommend to be less than 8 seconds. For solid country switching devices like an SSR driver or triac, faster switching times are better. Longer switching times, no thing what output type, let for more oscillation in the process value. The general rule is that, Merely if the process will permit it, when a relay output is used, a longer bicycle fourth dimension is desired.

Additional Features

Controllers tin also have a number of additional optional features. 1 of these is communication capability. A communication link lets the controller communicate with a PLC or a computer. This allows data exchange between the controller and the host. An example of typical information exchange would be the host figurer or PLC reading the process value.

A 2d pick is a remote setpoint. This characteristic allows a remote device, such every bit a PLC or computer, to modify the controller setpoint. However, unlike the advice adequacy mentioned to a higher place, the remote setpoint input uses a linear analog input signal that is proportional to the setpoint value. This gives an operator added flexibility past being able to change the setpoint from a remote location. A typical point might be iv–20mA or 0–10VDC.

Another mutual feature supplied with controllers is the ability to configure them using special software on a PC connected via a communications link. This allows quick and easy configuration of the controller and as well the option to save configurations for future employ.

Another mutual characteristic is a digital input. The digital input tin can work together with a remote setpoint to select the local or remote setpoint for the controller. It tin can likewise be used to select between setpoint 1 and setpoint ii as programmed in the controller. Digital inputs tin can also remotely reset a limit device if information technology has gone into the limit condition.

Other optional features include a transmitter power supply used to power a four–20mA sensor. This power supply is used to supply 24VDC power at a maximum of 40mA.

In some applications, a dual-color brandish tin can also be a desirable characteristic, making it easy to place different controller states. Some products also have displays that can change from red to greenish or vice versa depending on preprogrammed conditions, such as indicating an alert status. In this example, no alarm might be shown by a green brandish, merely if an warning is present the display would plow ruby-red.

Types of Controllers

Temperature controllers come in many unlike styles with a vast array of features and capabilities. There are too enough of means to categorize controllers according to their functional capabilities. In general, temperature controllers are either single loop or multi-loop. Single loop controllers take one input and one or more outputs to control a thermal system. On the other hand, multi-loop controllers accept multiple inputs and outputs, and are capable of controlling several loops in a process. More control loops permit controlling more than process organization functions.

Reliable single loop controllers range from bones devices that require single manual setpoint changes to sophisticated profilers that can automatically execute up to eight setpoint changes over a given time period.

Analog

The simplest, most basic controller type is the analog controller. Analog controllers are low cost, simple controllers that are versatile enough for rugged, reliable procedure control in harsh industrial environments including those with significant electrical noise. Controller display is typically a knob punch.

Basic analog controllers are used more often than not in not-critical or unsophisticated thermal systems to provide elementary ON-OFF temperature control for direct or reverse acting applications. Basic controllers accept thermocouple or RTD inputs and offer optional per centum power command manner for systems without temperature sensors. Their basic drawback is a lack of readable display and lack of sophistication for more challenging command tasks. Plus, the absence of whatever communication power limits their use to simple applications such as ON/OFF switching of heating elements or cooling devices.

Limit

These controllers provide safe limit control over process temperature. They have no ability to control temperature on their ain. Put simply, limit controllers are independent safety devices to be used alongside an existing command loop. They are capable of accepting thermocouple, RTD, or process inputs with limits prepare for high or low temperature just like a regular controller. Limit command is latching and part of redundant command circuitry to positively shut a thermal system down in case of an over-limit condition. The latching limit output must exist reset past an operator; it volition not reset by itself once the limit condition does not exist. A typical example would be a prophylactic shut off for a furnace. If the furnace exceeds some set temperature, the limit device would shut the system downwards. This is to prevent damage to the furnace and possibly any product that may exist damaged by excessive temperatures.

General Purpose Temperature Controllers

General-purpose temperature controllers are used to control well-nigh typical processes in industry. Typically, they come in a range of DIN sizes, take multiple outputs, and programmable output functions. These controllers can also perform PID control for excellent general control situations. They are traditionally placed in the front panel with the display for easy operator accessibility.

Near mod digital temperature controllers tin automatically summate PID parameters for optimum thermal organization performance using their built in auto-tuning algorithms. These controllers have a pre-melody part to initially calculate the PID parameters for a procedure, and a continuous melody function to constantly refine the PID parameters. This allows for quick setup, saving fourth dimension and reducing waste matter.

Valve Motor Drive

A special blazon of general-purpose controller is the valve motor drive (VMD) controller. These controllers are specifically designed to control valve motors used in manufacturing applications such equally gas burner control on a production line. Special tuning algorithms give accurate control and fast output reaction without the need for slidewire feedback or excessive noesis of 3-term PID tuning algorithms. VMD controllers command the position of the valve, somewhere between 0% to 100% open, depending on the free energy needs of the process at whatever given time.

Profile

Profiling controllers, also called ramp-soak controllers, allow operators to plan a number of setpoints and the time to sit at each setpoint. Programming a setpoint change is called ramp and the fourth dimension to stay at each setpoint is chosen soak or dwell. One ramp or i soak is considered to exist one segment. A profiler offers the ability to enter a number of segments to allow circuitous temperature profiles. The profiles tin be referred to as recipes by the operator. Near profilers allow storage of multiple recipes for later utilise. Smaller profilers may permit for iv recipes with sixteen segments each with more than advanced profilers allowing for more recipes and segments.

Contour controllers are able to execute ramp-and-soak profiles such as temperature changes over time, along with concur and soak/bike duration, all the while being unattended by an operator.

Typical applications for contour controllers include heat treating, annealing, environmental chambers, and complex process furnaces.

Multi-Loop

Besides single-loop controllers which can control only i process loop, multi-loop controllers can control more than than one loop, pregnant they tin can accept more than i input variable.

Generally speaking, a multi-loop controller can be thought of as a device with many private temperature controllers inside a single chassis. These are typically mounted behind the console equally opposed to in front of the panel as with general-purpose single loop controllers. Programming any one of the loops is similar to programming a console-mounted temperature controller. However, multi-loop systems tend not to have the traditional, physical user interface (no display or switches), instead using a dedicated communications link.

Multi-loop controllers need to be configured by a specialized software program on a PC that tin download the configuration to the controller using the dedicated communications interface.

Information tin can exist retrieved via a communications interface. Common communications interfaces that are supported include DeviceNet, Profibus, MODBUS/RTU, CanOPEN, Ethernet/IP, and MODBUS/TCP.

Multi-loop controllers provide a compact modular organisation that tin can operate either inside a stand up-alone system or in a PLC environment. As a replacement for temperature controls in PLCs, they provide fast PID control and off-load much of the math intensive work from the PLC processor, allowing for faster PLC scan rates. As a replacement for multiple DIN controllers, they provide a single point of software admission to all control loops. The cost of installation is reduced past eliminating much wiring, panel cutouts, and saving panel space.

Multi-loop controllers provide some additional features not available on traditional console mounted controllers. For instance, multi-loop controllers have higher loop density for a given space. Some multi-loop temperature control systems can accept upwardly to 32 loops of control in a DIN rail mounted parcel non much longer than 8". They also reduce wiring by having a common connectedness signal for power supply and communications interfaces.

Multi-loop temperature controllers also have enhanced security features, one of which is the absence of buttons where anyone tin modify critical settings. By having complete command over the information being read from or written to the controller, the automobile builder can limit the information that whatever given operator tin read or change, preventing undesirable atmospheric condition from occurring, such as setting a setpoint likewise high to a range that may damage production or the machine. In addition, controller modules tin be hot-swapped. This lets a controller module be changed out without having to power down the system. Modules can also auto-configure after a hot swap.

Other Temperature Controller Characteristics

Supply Voltage

There are typically two supply voltage options when information technology comes to temperature controllers: low voltage (24VAC/DC) and high voltage (110-230VAC).

Size

Controllers come up in several standard sizes that are referred to by DIN numbers such as ane/4 DIN, 1/8 DIN, one/16 DIN and 1/32 DIN. DIN is an acronym for the roughly translated "Deutsche Institut fur Normung," a German standards and measurements arrangement. For our purposes, DIN simply indicates that a device complies with a more often than not accepted standard for console dimensions.

DIN size comparison

DIN Size	1/4	i/8	1/16	1/32
Size in mm	92 ten 92	92 x 45	45 x 45	49 10 25
Size in inches	iii.62 x 3.62	3.62 10 1.77	1.77 x 1.77	1.93 ten 0.98

The smallest size is the 1/32 DIN, which is 24mm × 48mm, with a corresponding console cutout of 22.5mm × 45mm. The side by side size up is the 1/16 DIN which measures 48mm × 48mm with a panel cutout size of 45mm × 45mm. The 1/8 DIN is 48mm × 96mm with a 45mm × 92mm panel cutout. Lastly, the largest size is the 1/iv DIN measuring 96mm × 96mm with a 92mm × 92mm panel cutout.

It is of import to note that the DIN standards do non determine how deep a controller may be behind a panel. The standards only let for front panel dimensions and console cut-out dimensions.

Agency Approvals

It is desirable for a temperature controller to have some sort of agency approval to ensure that the controller meets a minimum ready of safe standards. The type of approval depends on the country in which the controller volition be used. The most mutual approval, UL and cUL registration, applies to all controllers used in the U.South. and Canada. Commonly, there is ane certification required for each country.

For controllers that are used in European Wedlock countries, CE approval is necessary.

A third type of approval is FM. This applies but to limit devices and for controllers in the U.S. and Canada.

Front Panel Enclosure Rating

An of import controller feature is the front console enclosure rating. These ratings tin be in the class of an IP rating or a NEMA rating. IP (Ingress Protection) ratings apply to all controllers and are ordinarily IP65 or higher. This ways that from the front panel only, the controller is completely protected from dust and against low pressure level jets of water from all directions with but express ingress permitted. IP ratings are used in the U.Due south., Canada, and Europe.

A controller's NEMA (National Electrical Manufacturers Association) rating is parallel to the IP rating. Most controllers have a NEMA 4 or 4X rating, which ways they can be used in applications requiring water washdown only (not oils or solvents). The 'X' in a NEMA 4X rating ways that the forepart panel won't corrode. NEMA ratings are used primarily in the U.Due south. and Canada.