An introduction to temperature control

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An Introduction to Temperature Control


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


3

Input

Sensor

Controller

Closed-loop control: Component parts

Heater

ControlDevice

Loop


4

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


5

• 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


6

• 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


7

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


8

Outputs Overview

There are 5 main output types

• Relay

• SSR Driver

• Triac

• Transmitter Power Supply

• DC Linear

>Volts

>Millivolts

>milliamps


9

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


10

Temp

On/Off Control

HysteresisSet-point

Output turns on

Time

Output turns off – just like home thermostat


11

Temp

Proportional Only Control

PropbandSet-point

100% power

0% power

Time

Offset - requires manual adjustment to remove


12

Temp

Conventional P.I.D. Control

PropbandSet-point

100% power

0% power

Time


13

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


14

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


15

Integral Time (minutes)

• Corrects proportional control offset error

• Too short - overshoots and oscillates

• Too long - slow warm-up and response

Too short Too long


16

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


17

Continuous (analogue) Control & Prop-Band

Temp

PropbandSetpoint

0% power

Time

20mA

4mA

100% power e.g. 65% power


18

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


19

Typical Start-up Auto-tuning

Temp

Setpoint

Start tune (self-learning) at 50% or 75% of setpoint

Time

Auto-tune completes & enters PID values


20

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


21

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


22

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


23

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


Thank you.

For more information please contact the Technical Support Team.

24 12. April 2023

http://west-cs.com/

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An introduction to temperature control