Temperature Measurement using sensors and signal conditioning

Michael MansellKen Dudeck (Faculty Sponsor)

Topics of Discussion

Types of temperature sensors The CK101 LCD Temperature

Meter Our circuit design

Types of temperature sensors

RTD (Resistance Temperature Detector)

Thermistor Thermocouple

RTD, the basics

How it works: Utilizes the fact that

resistance of a metal changes with temperature.

Make up: Traditionally made

up of platinum, nickel, iron or copper wound around an insulator.

Temperature range: From about -196°C

to 482°C.Thin Film RTD

RTD Advantages and Disadvantages

Advantages: Stable Very accurate Change in

resistance is linear

Disadvantages: Expensive Current source

required Small change in

resistance Self heating Less rugged than

thermocouples.

Thermistor, the basics of

How it works: Like the RTD a

thermistor uses the fact that resistance of a metal changes with temperature.

Make up: Generally made up

of semiconductor materials

Temperature Range: About -45°C - 150°C Thermistor

Thermistor Advantages and Disadvantages

Advantages: Very sensitive

(has the largest output change from input temperature)

Quick response More accurate

than RTD and Thermocouples

Disadvantages: Output is a non-

linear function Limited

temperature range.

Require a current source

Self heating Fragile

Thermocouple, some more basics

How it works: Made up of two

different metals joined at one end to produce a small voltage at a given temperature.

Make up: Made of up two

different metals. Ex: A type J is made up of Iron and Constantan.

Temperature Range Type J: 0°C to 750°C A few Thermocouples

Thermocouple Advantages and Disadvantages

Advantages: Self Powered

(does not require a current or voltage source)

Rugged Inexpensive Simple

Disadvantages: Extremely Low

Voltage output (mV)

Not very stable Needs a

reference point

Lets Experiment!

In lab a RTD, thermistor, and thermocouple were placed in a beaker of 750mL of water and readings were taken from 19°C to 80°C.

The next two slides show the results.

The Data (some of it)Temperature Thermocouple RTD Thermistor

(degrees Celsius) (mille-Volts) (ohms) (kilo-ohms)

19 -0.10 108.00 105.60

20 -0.10 108.40 99.80

21 0.00 108.70 94.20

22 0.00 109.00 88.20

23 0.00 109.50 83.80

24 0.10 110.00 79.70

25 0.10 110.40 75.90

26 0.10 110.90 73.30

27 0.20 111.30 70.00

28 0.20 111.50 68.40

29 0.30 112.00 63.40

30 0.40 112.90 60.50

32 0.50 113.20 54.80

34 0.70 114.10 49.20

36 0.70 114.80 45.50

A little easier to readThermocouple

-0.50

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

0 10 20 30 40 50 60 70 80 90

Temperature (∘C)

Vo

ltag

e (

mV

)

Thermistor

0.00

20.00

40.00

60.00

80.00

100.00

120.00

0 10 20 30 40 50 60 70 80 90

Temperature (∘C)

Res

ista

nce

(KΩ

)

RTD

100.00

105.00

110.00

115.00

120.00

125.00

130.00

135.00

0 10 20 30 40 50 60 70 80 90

Temperature (∘C)

Re

sist

an

ce (

Ω)

First test subject (The Kit CK101)

Basically the same idea as our circuit design, but easier?

How it works Why it did not

work

CK101 LCD Temperature Sensor

How it works and what went wrong

Uses transistors instead of the other discussed sensor types.

Uses the ICL 7106 chip

Problems: Possible Bad chip Capacitors not

soldered in properly. Cold solder joins

leading to bad connections

Our design

It works!

Picture

Another Picture

Circuit Diagram

49K

1K

1K

50K

1K

1K

50K

50K

-Vin

+

+-

+-

+-

+Vout

-

+

-Thermocouple

4.7μF

7417

1 2

5V 15V

Fan

Relay

Questions or Comments?

My Sources

Omega.com (Info on RTDs and Thermistors) http://www.omega.com/

United Electric Controls (Thermocouple, RTD, and Thermistor info) http://www.ueonline.com/

Intersil (ICL 7106 Chip reference) http://www.intersil.com/