Temperature Controllers and It's Types

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Temperature controllers Its Types

• By Nutronics India

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What is a Temperature Controller?

• A temperature controller is an instrument used to
  control temperatures, mainly without extensive
  operator involvement.
• A controller in this system will accept a
  temperature sensor such as a thermocouple or RTD
  as input and compare the actual temperature to
  the desired control temperature, or set point
  then provide an output to a control element.

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• A good example would be a heater or fan.
• The controller is usually just one part of a
  temperature control system while the whole system
  should be analyzed and considered in selecting
  the proper controller.

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Types of Temperature Controllers

• On/Off temperature Controller
• Proportional Control
• PID Control

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On/Off temperature Controller

• An on-off temperature controller is the simplest
  form of control device.
• The output from the device is either on or off,
  with no middle state.
• For heating control, the output is on when the
  temperature is below the set point, and off above
  set point.
• In cases where this cycling occurs rapidly, and
  to prevent damage to contactors and valves, an
  on-off differential, or "hysteresis," is added to
  the controller operations.
• On-off differential prevents the output from
  "chattering" or making fast, continual switches
  if the cycling above and below the setpoint
  occurs very rapidly.

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• On-off control is usually used in
• Where a precise control is not necessary
• In systems which cannot handle having the energy
  turned on and off frequently.
• Where the mass of the system is so great that
  temperatures change extremely slowly
• A temperature alarm.
• One special type of on-off control used for alarm
  is a limit controller. This controller uses a
  latching relay, which must be manually reset, and
  is used to shut down a process when a certain
  temperature is reached.

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Proportional Control

• Proportional controls are designed to eliminate
  the cycling associated with on-off control.
• A proportional controller decreases the average
  power supplied to the heater as the temperature
  approaches set point.
• This has the effect of slowing down the heater so
  that it will not overshoot the set point, but
  will approach the set point and maintain a stable
  temperature.
• This "time proportioning" varies the ratio of
  "on" time to "off" time to control the
  temperature.
• Outside this band, the temperature controller
  functions as an on-off unit, with the output
  either fully on (below the band) or fully off
  (above the band).
• At the set point (the midpoint of the
  proportional band), the output on-off ratio is
  11 that is, the on-time and off-time are equal.
  

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PID Control

• The third controller type provides proportional
  with integral and derivative control, or PID.
• This controller combines proportional control
  with two additional adjustments, which helps the
  unit automatically compensate for changes in the
  system.
• These adjustments, integral and derivative, are
  expressed in time-based units RESET and RATE,
  respectively.
• The proportional, integral and derivative terms
  must be individually adjusted or "tuned" to a
  particular system using trial and error.
• It provides the most accurate and stable control
  of the three controller types
• It is best used in systems which have a
  relatively small mass, those which react quickly
  to changes in the energy added to the process.
• It is recommended in systems where the load
  changes often and the controller is expected to
  compensate automatically due to frequent changes
  in set point.

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Common Uses in Industry

• Heat Treat/Oven
• Packaging
• Plastics
• Healthcare
• Food Beverage

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Display types of Temperature Controllers

• Digital Temperature Controllers

• Blind Temperature controllers

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Temperature Controllers by Nutronics India
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Digital Temperature Controllers by Nutronics India
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Blind Temperature Controllers by Nutronics India
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