an introduction to temperature control
TRANSCRIPT
WEST Control Solutions – Your global partner for measurement and control technology
An Introduction to Temperature Control
WEST Control Solutions – Your global partner for measurement and control technology
2
Thermostat
Basic temperature control (+/- 2˚ or 3˚)
Output switching18, 19, 20, 21, 22
Switching:on when under temp’
And off when over temp’
Room temperature measurement
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Input
Sensor
Controller
Closed-loop control: Component parts
Heater
ControlDevice
Loop
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Thermocouple
• B, C, J, K, L, N, R, S, T
Remote Setpoint
• Volts
• millivolts
• milliamps
• Potentiometer
DC Linear
• Volts
• millivolts
• Milliamps
RTD (Resistance Temperature Device)
• PT100
• NI120
Controllers have many types of inputs
Inputs
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• A thermocouple is made from two wires of different metal types, welded at one end (the “Hot” Junction).
• The wires are connected to the controller(the reference or “Cold” junction).
•When a difference in temperature exists between the “Hot” and “Cold” junctions, a small electric current will flow, in proportion to the temperature difference (this is called the thermoelectric effect).
Thermocouples
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• For the different types of metals various letters and colours are used.
• These colours vary from country to country but most now use the international IEC584 standard
Thermocouple Colour Codes
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RTD (Resistance Temperature Device)
• An RTD is made of a material that changes its resistance in a predictable way with changes in temperature
• There are many types of RTD the most common of which is the PT100 (Platinum Resistance Thermometer )
• The PT100 has a resistance of 100Ω at 0°C
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Outputs Overview
There are 5 main output types
• Relay
• SSR Driver
• Triac
• Transmitter Power Supply
• DC Linear
>Volts
>Millivolts
>milliamps
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Closed-loop control: Terminology
• LOAD - unit to be heated• HEATER - electrical or gas• INPUT - thermocouple, PT100, DC• CONTROLLER - decision making unit• OUTPUTS - solid-state relay (SSR)
- electro-mechanical relay- DC Volts or milliamps
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Temp
On/Off Control
HysteresisSet-point
Output turns on
Time
Output turns off – just like home thermostat
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Temp
Proportional Only Control
PropbandSet-point
100% power
0% power
Time
Offset - requires manual adjustment to remove
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Temp
Conventional P.I.D. Control
PropbandSet-point
100% power
0% power
Time
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Cycle-time (time proportioning)
On/Off
Cycle timee.g. 10 secs
Timeon
on
off
off
e.g. 50% power
on
on
on
off
on
on
on
on
off offoff
e.g. 75% power
off
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Cycle-time & Proportional bandTemp
PropbandSet-point
0% power
Time
on
off
Cyc’ time e.g. 10s
100% power
on
on
on
off off
e.g. 65% power
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Integral Time (minutes)
• Corrects proportional control offset error
• Too short - overshoots and oscillates
• Too long - slow warm-up and response
Too short Too long
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Derivative Time (seconds)
• Suppresses overshoots • Effects response time to disturbances• Too short - slow warm-up/response• Too short - under corrects• Too long - oscillates and over corrects
Too short Too long
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Continuous (analogue) Control & Prop-Band
Temp
PropbandSetpoint
0% power
Time
20mA
4mA
100% power e.g. 65% power
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Automatic Tuning
• Selects optimal PID values automatically
Start-Up Tuning
• Tests process when heating up
Tune at setpoint
• If process near ambient or can’t be interrupted
Continuous Tuning
• Monitors and adjusts if process moves from set-point
Tuning
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Typical Start-up Auto-tuning
Temp
Setpoint
Start tune (self-learning) at 50% or 75% of setpoint
Time
Auto-tune completes & enters PID values
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Temp
Typical Tuning at Set-point
Setpoint
Start tune (self-learning the process) @ 100% of setpointTime
Auto-tune completes & enters PID values
Overshoots during tuning
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Self-tune• Self-tune is a continuous improvement of the PID terms• Self-tune monitors for oscillations in the PV
• After 5 oscillations new PID terms are calculated
Setpoint 1
Setpoint 2
Load Disturbance
Setpoint Change
Temperature
Time
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Process Alarm Types
• Deviation high or low alarm
• Deviation band alarm
• Full-scale high or low alarm
Deviation high or low Band Full scale high or low
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Industry ApplicationsPlastics Extrusion, Blown-film extrusion, Hot-runners Window-frames
Packaging Bag sealers, Blister packaging, Wrapping
Food & beverage Ovens, Chillers, Packaging, Bottling, drying, Heat tunnels
Life sciences Incubators, Analytical equipment, Lab equipment, Sterilizers
Metals Foundries & furnaces, Metal treatment
Electrical, electronic Reflow ovens, Solder baths
Composite materials Autoclaves, Curing ovens
Glass & Ceramics Kilns & furnaces
Typical Applications
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Thank you.
For more information please contact the Technical Support Team.
24 12. April 2023