ACR Electronics SmartReader Plus Reference Manual page 84

SmartReader Plus Data Loggers
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place in refrigeration chamber of known temperature.
For 25°C, place logger in insulated box at a known temperature close to 25°C.
For 60°C, place the logger in a watertight bag and place in a warm water bath of known
temperature.
For all the rest, let the logger sit for about 2 hours to acclimatize. Record the times and
the known temperature for each.
4. Download the logger
After the tests are done, download the logger and graph the data. You should see 3 flat
spots on the resistance curve which correspond to the times of the temperature tests.
Record the value of each of the three spots.
5. Generate a thermistor equation
From the Equation Menu, create a thermistor equation (using the equation wizard). Enter
the low, mid and high temperatures and the corresponding resistances. Generate the
equation.
6. Revise the Logger File
Revise the logger file and change the equation of the internal temperature channel from
your resistance equation to the new Thermistor Equation.
7. Graph the file
Make sure the units are in Celsius. Check to make sure that the three flat spots occur at
the known temperatures.
8. Add three compound lines
On the graph, add the three compound lines. Each line should use the Thermistor
equation you just created. For each of them, set the Source0 variable to Constant. The
value of Constant should be 16.24 for the first line, 127.5 for the second line and 195.194
for the third line. These values correspond to the byte value that corresponds to 100, 25,
0°C under equation 45.
9. Show the graph as a table
Expand the data section of the graph to view the data points. Note the value of each of
the three compound lines. The first line should be close to 100°C, record that
temperature as T3. The second line should be close to 25°C, record that temperature as
T2. The last line should be close to zero, record that temperature as T1.
10. Calculate the Low, Mid and High Calibration constants
The Low value should be equal to T1
The Mid value should be equal to T2 - 25
The High value should be equal to 100 - T3
11. Final check
Revise the logger file again. This time, set the equation to 45 and enter the new
calibration constants. Save the file under a new name. Open this new file and the first
file (using the custom thermistor equation) into the same graph. Both lines should match
perfectly.
12. Calibrate the logger
Enter the new calibration values into the logger, set the equation to 45 and save the new
changes.
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