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An Introduction to
Temperature Control

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Basic temperature control (+/- 2˚ or 3˚)
Thermostat
Output switching 18, 19, 20, 21, 22
Room temperature
measurement
Switching:
on when under temp’
And off when over temp’
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Closed-loop control: Component parts
Controller
Control
Device
Loop
Heater
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Inputs
Controllers have many types of inputs
Thermocouple DC Linear
• B, C, J, K, L, N, R, S, T • Volts
• millivolts
Remote Setpoint • Milliamps
• Volts
• millivolts RTD (Resistance Temperature Device)
• milliamps • PT100
• Potentiometer • NI120
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Thermocouples
• 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).
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Thermocouple Colour Codes
• 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
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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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On/Off Control
Temp Output turns off – just like home thermostat
Set-point
Hysteresis
Output turns on
Time
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Proportional Only Control
Temp Offset - requires manual
adjustment to remove
0% power
Prop
Set-point band
100% power
Time
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Conventional P.I.D. Control
Temp
0% power
Prop
Set-point band
100% power
Time
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Cycle-time (time proportioning)
On/Off
e.g. 50% power
on off on off on off on
Time
Cycle time
e.g. 10 secs e.g. 75% power
on off on off on off on off
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Cycle-time & Proportional band
Temp
Prop
Set-point
band
100% power
0% power e.g. 65% power
Time
on
on on on off off
off
Cyc’ time e.g.
10s
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Integral Time (minutes)
Too short Too long
• Corrects proportional control offset error
• Too short - overshoots and oscillates
• Too long - slow warm-up and response
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Derivative Time (seconds)
Too short Too long
• Suppresses overshoots
• Effects response time to disturbances
• Too short - slow warm-up/response
• Too short - under corrects
• Too long - oscillates and over corrects
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Continuous (analogue) Control & Prop-Band
Temp
Prop
Setpoint
band
100% power
0% power e.g. 65% power
Time
20mA
4mA
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Tuning
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
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Typical Start-up Auto-tuning
Temp
Auto-tune completes & enters PID values
Setpoint
Start tune (self-learning) at 50% or 75% of setpoint
Time
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Typical Tuning at Set-point
Temp
Overshoots during tuning
Setpoint
Auto-tune completes & enters PID values
Start tune (self-learning the process) @ 100% of setpoint
Time
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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
Temperature
Setpoint 2
Load
Disturbance
Setpoint 1
Setpoint
Change
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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Typical Applications
Industry Applications
Plastics 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
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Thank you.
For more information please contact the Technical
Support Team.
Juni 12 24