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: Temperature range: 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 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 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 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 20 108.40 99.80 21 0.00 108.70 94.20 22 109.00 88.20 23 109.50 83.80 24 0.10 110.00 79.70 25 110.40 75.90 26 110.90 73.30 27 0.20 111.30 70.00 28 111.50 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 36 114.80 45.50

A little easier to read

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

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/