Interpreting Temperature Logger Data Changing Digitized Temperature Readings back into Temperatures Before you can begin programming your Temperature Logger, you will need to understand the three types of memory inside the PICAXE-08M2

Analog Temperature Readings to Digital Values Analog: 0 to 5 volts Digital: 0 to 255 D = (A/5) X 256 The PICAXE can convert any voltage between zero and five volts into a digital value between 0 and 255. This is a linear conversion, so zero volts becomes a digital zero, 2.5 volts becomes a digital 127 (or 128 depending on the accuracy of the 2.5 volts), and five volts becomes a digital 255. You can calculate the digital value of any analog voltage by dividing it by 5 And then multiply by 256. Since the PICAXE does not use decimal points, you need to round up the calculated value.

The LM335 Temperature Sensor Temperature: 0 to 500 kelvins Output: 0 to 5 volts The LM 335 Temperature Sensor produces a voltage that varies linearly with its temperature. Theoretically, it will produce zero volts at absolute zero and five volts at a temperature of 500 kelvins (which is the same as 435 degrees Fahrenheit).

Four Temperature Scales Kelvin Celsius Fahrenheit Rankin There are four popular temperature scales. The temperature scales of Kelvin and Celsius have the same size degrees, but kelvin begins measuring the temperature at Absolute Zero. The temperature scales of Fahrenheit and Rankin have the same size degree (which is different from Kelvin and Celsius), but Rankin begins measuring the temperature at Absolute Zero. Kelvin and Rankin are scientific and engineering scales, that’s why they begin measuring form Absolute Zero. This means there can never be a negative temperature reading in Kelvin and Rankin. To convert Celsius into Kelvin, just add 273 to the temperature in Celsius. To convert Fahrenheit into Rankin, just add 459 to the temperature in Fahrenheit. To convert Celsius into Fahrenheit and back again is a little more difficult. But the next slide will show you a trick that you can use.

Fahrenheit and Celsius There are 1.8 Fahrenheit degrees in 1 Celsius degree -40O Fahrenheit = -40O Celsius There is 1.8 Fahrenheit degrees in one Celsius degree. The inverse is also true, so that there is 5/9 of a Celsius degree in one Fahrenheit degree. It’s also true that -40 degrees is the same temperature in both temperature scales. This means if you plot the temperature in Celsius and Fahrenheit on any other temperature scale, the two lines representing the temperature in Celsius and Fahrenheit would cross at -40 degrees Celsius (or Fahrenheit). This means that if we adjust either of the temperature scales to -40 degrees, the only difference between the two temperature scales is just their slopes. So here is the process to convert Celsius to Fahrenheit. 1. Add 40 to the temperature in Celsius 2. Multiply the new temperature by 1.8 3. Subtract 40 from the new value You can reverse this process and easily convert the temperature in Fahrenheit into Celsius. 1. Add 40 to the temperature in Fahrenheit 2. Divide the new temperature by 1.8

Converting a Digitized Temperature back into Temperature Temperature (k) = R/256 X 500 To convert a digitized temperature reading back into the temperature in Kelvin, you need to take the digitized value and divide it by 256 (the largest number that can be stored in a byte-size memory). Then multiply the result by 500 Kelvins. Now you can convert the temperature in Kelvins into Celsius and from there into Fahrenheit and Rankin.

Spreadsheet Helper Included with the Temperature Logger Along with the Temperature Logger is a spreadsheet for converting digitized temperature readings into temperatures in the Kelvin, Celsius, Fahrenheit, and Rankin scales. But rather than copy the temperature readings into the spreadsheet, create a new spreadsheet from the output form the Temperature Logger and copy the spreadsheet equations into cells. Let’s see how to do this.

Transferring Temperature Data into Notepad Temperature readings are not useful in the Terminal program Copy into Notepad using the Copy Input Buffer option When the Temperature Logger downloads its readings into the PICAXE Editor’s Terminal Program (it can be started by pressing the F8 key), it will be a series of numbers, separated by commas. You cannot use or edit the values while it remains in the Terminal program. So click Edit and two options will appear in the drop down menu. Click the second one, Copy Input Buffer. This copies the data so that it can be pasted into a text editor (use Notepad for this).

This is where you will find the Copy Input Buffer option.

Editing Temperature Data You get: 144,145,146,148 Edit to make it: 144 145 146 148 When you get digitized temperature readings from the Temperature Logger and paste it into Notepad, it will be a series or temperature readings, each separated by a comma. You will need to edit it into a single column of digitized temperature readings with no commas.

In Excel, you will need to select Text Files in the Files of Type window.

Excel will ask if the file is delimited. So click the Next button Excel will ask if the file is delimited. So click the Next button. On the following two windows click the Next and then the Finish buttons.

After the data is imported into Excel, then copy and paste the four equations needed to convert the digitized temperature data into Kelvin, Celsius, Fahrenheit, and Rankin. You should also create a column for the time of each reading. This depends on how frequently you program your Temperature Logger to record data. However, in the this example, the Temperature Logger was programmed to collect temperature readings every one minute.

Now you can create a chart to display your temperature readings Now you can create a chart to display your temperature readings. Be sure to save your file as a spreadsheet.