An Introduction To Sensors - Temperature Sensors

Laboratory Exercise - Sensors

Measuring Sensor Characteristics

In another lab exercise, you measured some voltages from these three temperature sensors.

Here is some background information about these sensors from that lesson.

Thermocouples, which are inexpensive and widely used. However, thermocouples produce a voltage out that is in the millivolt range. Here is a photo of a thermocouple.

Thermistors are temperature sensitive resistors. Here is a photo of a thermistor.

Integrated circuit temperature sensors, like the LM35, are designed to produce a voltage that is directly proportional to temperature. Here is a photo of an LM35 integrated circuit temperature sensor.

We will look at the time response of all three of these sensors. Here is what to do.

Measure the temperature of the thermocouple using a pre-written program. Get a complete transient both going up and going down. Be sure that you store the data in two separate files. Call those files TCUp and TCDown.
You will need to connect the LM35. Click here to get the circuit for the LM35. Wire it up (And record the circuit in your lab notes.) and measure the complete transient both going up and going down. Be sure that you store the data in two separate files. Call those files LM35Up and LM35Down.
Use a voltage divider circuit for the thermistor. (That may be pre-wired. Record the circuit in your lab notes.) Get a complete transient both going up and going down. Be sure that you store the data in two separate files. Call those files TRUp and TRDown.

Note, for this sensor, you will need to compute the temperatures from the voltage data. You will need to know the resistance characteristics of the thermistor, and the values of resistance and voltage for the divider.

Now, keep the data and go on to the next lab where you will analyze the data you have collected.

Using a Data Acquisition Unit (DAU) measure the temperature using the temperature capabilities of the DAU. (You need a DAU to do this.)

Finally, do the following.

Measure the voltage across the thermistor at room temperature and at body temperature.
Measure the resistance of the thermistor at room temperature and at body temperature.

You will need to use the resistance measurement capabilities of your instrument.

For your report answer the following questions.

Which sensor produces the largest voltage as temperature changes between room temperature and body temperature? In other words, which sensor is the most sensitive?
Does any sensor have a voltage so small that it might be difficult to measure?
Which sensor woud require some circuitry in order to make it a usable sensor (one that produces a voltage output)?
Order the sensors from slowest to fastest as best you can.
Which sensor do you find easiest to use? Why?