2. Temperature Measuring and Control
Temperature Introduction .................................................................................................. 1
Practical Learning Processes / Task TC and RTD.............................................................. 2
Types of Thermocouples................................................................................................... 3
Thermocouple Colour coding and Identification ................................................................. 4
Temperature Measuring and Control Panel........................................................................ 5
Temperature Measuring and Control Loop Diagram ......................................................... 6
Temperature Measuring and Control Wiring ...................................................................... 7
Temperature Measurement and Control PD&I.................................................................... 8
Temperature Panel Start-Up Sequence ............................................................................. 9
Formative Practical Assessment...................................................................................... 10

3. Thermocouples
Seebeck effect
The Seebeck effect is the conversion of temperature differences directly into electricity and is named after the Baltic German physicist Thomas Johann
Seebeck. Seebeck, in 1821, discovered that a compass needle would be deflected by a closed loop formed by two different metals joined in two places, with a
temperature difference between the junctions. This was because the metals responded to the temperature difference in differen t ways, creating a current loop
and a magnetic field. Seebeck did not recognize there was an electric current involved, so he called the phenomenon the thermomagnetic effect. Danish
physicist Hans Christian rectified the mistake and coined the term "thermoelectricity".
The Seebeck effect is a classic example of an electromotive force (emf) and leads to measurable currents or voltages in the same way as any other emf.
Electromotive forces modify Ohm's law by generating currents even in the absence of voltage differences (or vice versa); the local current density is given by
Peltier effect
The Peltier effect is the presence of heating or cooling at an electrified junction of two different conductors and is named after French physicist Jean Charles
Athanase Peltier, who discovered it in 1834. When a current is made to flow through a junction between two conductors A and B, heat may be generated (or
removed) at the junction. The Peltier heat generated at the junction per unit time, is equal to
where ( ) is the Peltier coefficient of conductor A (B), and is the electric current (from A to B). Note that the total heat
generated at the junction is not determined by the Peltier effect alone, as it may also be influenced by Joule heating and thermal gradient effects
Thomson effect
In many materials, the Seebeck coefficient is not constant in temperature, and so a spatial gradient in temperature can result in a gradient in the
Seebeck coefficient. If a current is driven through this gradient then a continuous version of the Peltier effect will occur. This Thomson effect was
predicted and subsequently observed by Lord Kelvin in 1851. It describes the heating or cooling of a current-carrying conductor with a temperature
gradient.
If a current density is passed through a homogeneous conductor, the Thomson effect predicts a heat production rate per unit volume of:
where is the temperature gradient and is the Thomson coefficient. The Thomson coefficient is related to the Seebeck coefficient as . This
equation however neglects Joule heating and ordinary thermal conductivity
Temperature Introduction

4. RTD
Wiring configurations
Two-wireconfiguration
The simplest resistance thermometer configuration uses two wires. It is only used when high accuracy is not required, as the resistance of the connecting
wires is added to that of the sensor, leading to errors of measurement. This configuration allows use of 100 meters of cable. This applies equally to balanced
bridge and fixed bridge system.
Three-wire configuration
In order to minimize the effects of the lead resistances, a three-wire configuration can be used. Using this method the two leads to the sensor are on adjoining
arms. There is a lead resistance in each arm of the bridge so that the resistance is cancelled out, so long as the two lead resistances are accurately the same.
This configuration allows up to 600 meters of cable

5. Four-wireconfiguration
The four-wire resistance configuration increases the accuracy of measurement of resistance. Four-terminal sensing eliminates voltage drop in the measuring
leads as a contribution to error. To increase accuracy further, any residual thermoelectric voltages generated by differentwire types or screwed connections
are eliminated by reversal of the direction of the 1 mA current and the leads to the DVM (Digital Voltmeter). The thermoelectric voltages will be produced in
one direction only. By averaging the reversed measurements, the thermoelectric error voltages are cancelled out.
Classifications of RTDs
The highest accuracy of all PRTs is the Standard platinum Resistance Thermometers (SPRTs). This accuracy is achieved at the expense of durability and
cost. The SPRTs elements are wound from reference grade platinum wire. Internal lead wires are usually made from platinum while internal supports are
made from quartz or fuse silica. The sheaths are usually made from quartz or sometimes Inconel depending on temperature range. Larger diameter platinum
wire is used, which drives up the cost and results in a lower resistance for the probe (typically 25.5 ohms). SPRTs have a wide temperature range (-200 °C to
1000 °C) and approximately accurate to ±0.001 °C over the temperature range. SPRTs are only appropriate for laboratory use.
Another classification of laboratory PRTs is Secondary Standard platinum Resistance Thermometers (Secondary SPRTs). They are constructed like the
SPRT, but the materials are more cost-effective. SPRTs commonly use reference grade, high purity smaller diameter platinum wire, metal sheaths and
ceramic type insulators. Internal lead wires are usually a nickel-based alloy. Secondary SPRTs are limited in temperature range (-200 °C to 500 °C) and are
approximately accurate to ±0.03 °C over the temperature range.

6. Practical Learning Processes / Task TC and RTD
OBJECTIVES (WHAT YOU MUST DO / EXPECTATIONS)
1. A learner must be able to select and test a correct working TC or RTD and connect it to the corresponding TC/RTD
compensating leads Field Work. Calibrate PUK accordingly, Draw a loop diagram for Temperature Measuring and control,
Connect up the loop completely, do a sequential safety start-up system, Pre-Heat the Ove MANUALLY and slowly to the
required SP, Switch to AUTOMATIC and do the Final Loop Tune to the (PID) system for correct optimization of the Temperature
loop.
2. Work safe using all the Safety working procedures and manufacture’s manuals accordingly.
3. Calculate and give all the required values accordingly. (Tolerance ± 3°C)
4. Compare the three READINGS and Recorded trends from the front Oven and state the three factors that will affect the
measuring in the Oven using thermocouples.
WHAT YOU WILL BE GIVEN
 All the necessary equipment e.g. Oven, Temp. Controller, PUK, TC or RTD, Calibration system tool, Information book and testing
tools.
HOW WELL YOU MUST DO IT
 On completion: If there is any disturbance/upset to the running process, a three step correcting quarter wave dumper should be
obtained after any process upset from the Oven.
ADDITIONAL RESOURCES
 Your Training and Development Officer
 Process instrumentation and Controls Handbook by the TDO

7. Types of Thermocouples
Type J
Type J (iron – constantan) has a more restricted range than type K (−40 °C to +850 °C), but higher sensitivity of about 50 µV/°C. The Curie point of the iron
(770 °C) causes a smooth change in the characteristic, which determines the upper temperature limit.
Type K
Type K (chromel – alumel) is the most common general purpose thermocouple with a sensitivity of approximately 41 µV/°C (chromel positive relative to alumel
when the junction temperature is higher than the reference temperature). It is inexpensive, and a wide variety of probes are available in its −200 °C to
+1350 °C / -330 °F to +2460 °F range. Type K was specified at a time when metallurgy was less advanced than it is today, and consequently characteristics
may vary considerably between samples. One of the constituent metals, nickel, is magnetic; a characteristic of thermocouples made with magnetic material is
that they undergo a deviation in output when the material reaches its Curie point; this occurs for type K thermocouples at around 185 °C.
Type T
Type T (copper – constantan) thermocouples are suited for measurements in the −200 to 350 °C range. Often used as a differential measurement since only
copper wire touches the probes. Since both conductors are non-magnetic, there is no Curie point and thus no abrupt change in characteristics. Type T
thermocouples have a sensitivity of about 43 µV/°C. Note that copper has a much higher thermal conductivity than the alloys generally used in thermocouple
constructions, and so it is necessary to exercise extra care with thermally anchoring type T thermocouples.
Platinum/rhodium alloy thermocouples
Types B, R, and S thermocouples use platinum or a platinum/rhodium alloy for each conductor. These are among the most stable thermocouples, but have
lower sensitivity than other types, approximately 10 µV/°C. Type B, R, and S thermocouples are usually used only for high temperature measurements due to
their high cost and low sensitivity.
Type B, S, R
Type B thermocouples (Pt/Rh 70%/30% – Pt/Rh 94%/6%, by weight) are suited for use at up to 1800 °C. Type B thermocouples produce the same output at
0 °C and 42 °C, limiting their use below about 50 °C. The emf function has a minimum around 21 °C, meaning that cold junction compensation is easily
performed since the compensation voltage is essentially a constant for a reference at typical room temperatures.

8. Thermocouple Colour coding and Identification
Type
Positive metal
physical
properties
Positive (+) Negative (-)
Negative metal
physical
properties
Braiding
colour
Colour of
compensati
ng cable (+)
Colour of
compensati
ng cable (-)
Temperature
range (ºC)
K Non magnetic Chromel Alumel Slightly magnetic Yellow Yellow Red -180 to +1350
J Magnetic Iron Constantan Non magnetic Black White Red -180 to +850
T Copper colour Copper Constantan Non magnetic Blue Blue Red -250 to +400
S Hard
Platinum +
10%
Rhodium
Platinum Soft Green Black Red -50 to +1750
R Hard
Platinum +
05%
Rhodium
Platinum Soft Green Black Red -50 to +1950

9. THERMOCOUPLE / RTD
CONTROLLER
K RTD
R/S
TJ
Temperature Measuring and Control Panel

10. Local Sp
L N
TIC
K
Temp Transmitter
TC
Heat Element
OvenTemp
220v Sup
SolidState Relay
24v AC Sup
4 - 20mA
4 - 20mA
mV
Temperature Measuring and Control Loop Diagram
Input
Output

11. Main
Sup
220VAc
P/S
24v DC
220V Ac
220v AC
24v AC
SSR
OVEN
TIC
T.Tx
4 - 20mA
4 - 20mA
Temperature Measuring and Control Wiring
24v dc Supply
220V AC Switching for TempControl
0 - 200°C L Sp

12. 6 5 4 3 2 1
D
FIELD FRONT CONNECTOR (BANANA PLUGS) I/O LANDING STRIP HONEYWELL CONTROLLER
(AI,AO,DO)
O N
O L
O L
O 4 AL (1)
O 5 COMM
O 6
O 7
O 8
O 9 OUTPUT 1
O 10
O 11
O 12
O 13
O 14
O 15
O 16
O 17
O 18 INPUT 1
O 19
O 20
O 21
O 22
O 23
O 24
O 25
O 26
O 27
Designed JMK 10/02/2015 Area : AGA Engineering Centre
Revised Project:
Checked JMK 10/02/2015 Project: PAGE No 1
Approved ZS 10/02/2015 Title: LOCAL TEMP CONTROLLER
DRAWING
No OF PGS 1
D
C C
B
B
A
A
6 5 4 3 2 1
TEMPERATURE MEASURING AND CONTROL PD&I
LS
DO
AI
AO
+ O
+ O
- O
+ O
- O
INPUT
4 – 20mA
OUTPUT
4 - 20mA
- O
+ O
- O
+ O
- O
Tx
SSR
24V SUP
220V SUP
Controlled
mV
SolPne

13. Temperature Panel Start-Up Sequence
Q1
Q1-A
Start Stop
Q1-A
Red Light
Power
available on
the Panel
Green Light
Panel ready
Start-up
Relay
24v DC
220v AC MainSup
220v AC PowerSupply to the whole
Panel
Q1-B

14. Formative Practical Assessment
Measuring and Control
 Selecta type …………………… thermocouple/RTD from the rest and connect it correctly to the corresponding
TC compensating leads/RTD leads.
 Calibrate PUK accordinglyfor the ………0°C …………To………200°C ………. range temperature,
 Draw a loop diagram forTemperature Measuring and control,
 Connect up the loop completelyaccording to the loop drawing,
 Perform the sequential safety start-up system for your panel,
 Pre-Heat the Oven temperature MANUALLY and SLOWLYto the required SP……………….°C,
 Switch the controller to AUTOMATIC and do the Final Loop Tune to the (PID) system for correctoptimization of
the Temperature loop.
 Create a step change to the processand note the
1
4
Wave form from the recorder,
 Answer the following question: *
 What is the real current temperature in the Oven?
 For this temperature, what is the mA current from the Transmitter?
 For this PUK output, what is the input value and units?
 State the three factors that will affectthe measuring in the Oven using
thermocouples.

15. RTD Process
PRACTICAL ASSIGNMENT MEASURING AND CALCULATIONS
1. Check a R.T.D. temperature Indicator.
a. Disconnect the R.T.D leads on the indicator provided, make note of the connections.
b. Connect a Decade resistance Box, or a R.T.D. simulator to the indicator.
c. Using the Resistance to Temperature Tables supplied at the end of the module, apply the resistance value equal to 0ºC by means of
the Decade box of the R.T.D. simulator.
d. The indicator should indicate 0ºC.
e. Apply the resistance value equal to the upper range value by using the Decade box or the R.T.D. simulator.
f. The indicator should indicate the upper range temperature.
2. Calibrate a R.T.D. transmitter.
a. Connect a 24 v D/C supply to the output side of a R.T.D. transmitter. Make sure that the polarities of the connections are correct.
b. Connect a mA meter in series with the 24v D/C supply and the transmitter.
c. Connect a Decade resistance box or a R.T.D. simulator to the input of the transmitter.
d. Using the Resistance to Temperature Tables supplied at the end of the module, apply the resistance value equal to 0ºC by means of
the Decade box or the R.T.D. simulator.
e. Adjust the Zero setting to obtain a reading of 4mA.
f. Apply the resistance value equal to the upper range value by using the Decade box or the R.T.D. simulator.
g. Adjust the Span setting to obtain a reading of 20mA.
h. Repeat steps d to g until the unit is calibrated accurately.

16. Thermocouple Process
PRACTICAL ASSIGNMENT MEASURING AND AVARAGE TEMPERATURE CALCULATIONS
Using the equipment assigned to you, you must do the following tasks.
1. Select types “J”, “K” and “T” thermocouples.
2. Connect the correct extension leads to the thermocouples.
3. Place the thermocouples in the oven and allow 10 minutes for the temperature to stabilize before continuing with step 4.
4. Using a Multi-meter, measure the millivolts from each thermocouple.
5. Using the Temperature / Millivolt tables, convert the millivolts readings to ºC.
6. Give the actual temperature in the oven, as measured by the three thermocouples.
7. Ask your Training Officer to check your work.
When you feel satisfied with your knowledge of this module, ask the Training Officer for the Criterion test.