It is possible to manually calibrate a sensor, but in most cases it is not necessary. However, for optimum accuracy you may choose to calibrate manually.
To perform any calibration you will need one or more external references for your sensor. For example, to do a two-point calibration for a pH sensor you’ll need two solutions of known and widely-separated pH. Your calibration is only as good as your knowledge of these reference values.
A two-point calibration is always better than a one-point calibration, but sometimes it is more convenient to adjust the sensor reading to a single reference.
Specific manual calibration instructions are provided in the booklets that come with the sensor. They can also be viewed from the Vernier web site.
A Live Calibration uses external references whose values are widely seperated and on either side of the intended readings you anticipate in you experiment. For the example below using the pH sensor, a solutions of pH 4 and ph 10 could be used.
- Choose Setup Sensors from the Experiment menu, and select the interface you have connected.
- Click the channel the sensor is connected to and choose Calibrate...
- A dialog box will appear. Click Calibrate Now to begin the calibration process. The current output(s) of the sensor is shown in the input fields. Enter the appropriate Unit and/or Symbol.
- Place the sensor in the first calibration environment. (e.g. a known pH)
- Place the sensor in the second calibration environment.
- Once the readings in the input field(s) stop changing significantly, click Keep to record the input value(s). If you are performing a one-point calibration (see below), click Done to complete the process.
- Place the sensor in the second calibration environment. (e.g. the other known pH)
- Enter the known calibration value in the Reading 2 box.
- Once the readings in the input field(s) stop changing significantly, click Keep to record the input value or values. After the last Keep button is clicked, a new calibration is created. It is added to the list of available calibrations and it is marked as Not Saved. This new calibration becomes the current calibration for the sensor.
- If you want to use the calibration for the current session only, click Done to complete the calibration process. There are several ways to store a custom calibration. See the Calibration Storage dialog for these options.
- Select Done to complete the calibration process.
A single point calibration assumes that the slope for a sensor's calibration is good and that only the intercept needs to be adjusted (these are all linear calibrations: y = mx + b).
Some sensors (e.g. Go! Temp) will default to single point. Others will have single point available as a check box in the calibration dialog but it won't be the default.