# Hands-On-PhysicsHEAT & TEMPERATURE

## - Calibration -

To get accurate measurements from a sensor, you have to calibrate. In this activity, you calibrate one of the sensors for later use. Calibrating your sensors lets you convert your readings into temperature. For instance, calibration would let you convert the resistance readings from a thermistor into degrees. Your goal is to come up with a way of converting "raw data", the readings on your meter, to temperature. The following sketch suggests one way. Calibration always involves two measuring devices. To calibrate, you compare readings from a standard device to the readings of the sensor you are calibrating.

Figure M6
Scheme for Calibration of a Sensor

In the calibration curve shown below, five data points, indicated by crosses, have been taken across a range of temperatures. Then a smooth curve, shown in green, was fit to these data. Later, if you measure a resistance, a, shown in blue, then this reading can be converted to a temperature, b, shown in red.

Figure M7
Calibration cure

### Steps in Calibration

• Pick the standard you are going to use for measuring temperature:
You can use a good lab thermometer, an electronic thermometer, or one of the integrated circuits, the AD590 or the LM335. Next, pick the sensor you will callibrate­p;it can be a thermistor, diode, thermocouple, or one of the integrated circuits. Each sensor may be a bit different from the next, so put a tag on the sensor you calibrate so you can identify it later.

• Think and plan:
What is your goal? Over what range of temperatures do you need accurate calibration? How can you keep errors to a minimum? How much data will you need? Write your group's questions and answers in a lab notebook.

• Take Data:
Take pairs of readings at each temperature. Each pair consists of a temperature according to your standard and the raw data from your sensor. Take these carefully when the temperatures of the standard and sensor are exactly the same. Be as accurate as possible. Take enough pairs to give you an accurate graph over the entire range that you will need.

• Make a Calibration Curve:
Generate a graph like the one above using your data. Use a graphing spreadsheet if one is available. Make it clear what data you took and then draw a smooth curve through these data.