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 -0.10 108.00 105.6020 -0.10 108.40 99.8021 0.00 108.70 94.2022 0.00 109.00 88.2023 0.00 109.50 83.8024 0.10 110.00 79.7025 0.10 110.40 75.9026 0.10 110.90 73.3027 0.20 111.30 70.0028 0.20 111.50 68.4029 0.30 112.00 63.4030 0.40 112.90 60.5032 0.50 113.20 54.8034 0.70 114.10 49.2036 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)
Vol
tage
(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)
Res
ista
nce
(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/