Temperature Measurement using
sensors and signal conditioning
Michael Mansell
Ken 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:


Make up:


Utilizes the fact that
resistance of a metal
changes with
temperature.
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:


Make up:


Like the RTD a
thermistor uses the fact
that resistance of a
metal changes with
temperature.
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 nonlinear function
Limited
temperature range.
Require a current
source
Self heating
Fragile
Thermocouple, some more basics

How it works:


Make up:


Made up of two
different metals joined
at one end to produce
a small voltage at a
given temperature.
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
(degrees Celsius)
Thermocouple
RTD
Thermistor
(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 read
RTD
3.50
135.00
3.00
130.00
Resistance (Ω)
2.50
2.00
1.50
1.00
0.50
125.00
120.00
115.00
110.00
105.00
0.00
100.00
-0.50
0
10
20
30
40
50
60
70
80
0
90
10
20
30
40
50
Temperature (∘C)
Temperature (∘C)
Thermistor
120.00
100.00
Resistance (KΩ)
Voltage (mV)
Thermocouple
80.00
60.00
40.00
20.00
0.00
0
10
20
30
40
50
Temperature (∘C)
60
70
80
90
60
70
80
90
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
+
-
1
1K
2
50K
7417
49K
+
-
Vin
+
Thermocouple
+
Vout
4.7μF
+
1K
5V
+
-
1K
50K
1K
Relay
15V
50K
Fan
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/