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4.
Insert the thermometer and the thermistor probes into the bucket ensuring that they do
not touch the side or bottom of the bucket. Make sure the thermistor probes' leads are
long enough for you to easily take resistance readings.
5.
Cover the bucket with foam chips or another suitable insulating material. Let sit for at
least five minutes while the temperature stabilizes and the thermistor has a chance to
respond. Add more ice periodically, as before, ensuring that it is tightly packed to the
bottom of the bucket each time. The goal is to keep the thermistor completely
submerged in the ice slurry until it reaches 0°C (32°F).
6.
Measure and record the resistance of the thermistor probe from the logger and the
temperature from the thermometer. This is the Low temperature calibration point value.
7.
Now insert the thermistor probe into a pot of water at room temperature and bring to a
boil. Record the resistance of the thermistor probe. This is the High calibration point
value 100°C (212°F).
8.
With TrendReader software, create a thermistor equation (using the equation wizard)
from the Equation Menu. Save the equation to the logger.
CAUTION: To avoid damaging your thermistors, when calibrating, make sure you
do not introduce the sensors to rapid changes in temperature (for example, from
ice bucket right into the boiling water).
Calibration Procedure for Temperature Equation 45
This procedure describes how to calibrate equation 45 in TrendReader software.
Normally, you would calibrate a sensor by exposing it to 3 temperatures (0, 25 and 100°C) and
entering the difference of (Measured Temperature - Actual Temperature) as Low, Mid and
High calibration values. This works fine for our ET-016 temperature probes. Unfortunately,
this is not possible for internal sensors since the electronics on the data logger cannot
withstand a temperature of 100°C. You can simulate the calibration at 0, 25 and 100°C by
creating a custom thermistor curve based on temperatures of 0, 25 and 60°C, extrapolating
the curve to 100°C, and using that value for normal calibration.
TrendReader Procedure:
1.
Write a resistance equation
Create a custom equation of the form:
SRC = Source0
if SRC < 1 then SRC = 1
if SRC > 254 then SRC = 254
R = 10000 * SRC / (255 - SRC)
Answer0 = R
Save this equation.
2.
Set the internal temperature channel of the logger to the resistance equations
Setup the logger, change the equation number to that of the resistance equation, and
save changes. Sample rate should be fairly long (about 5 minutes is good). All
calibration values on the internal channel should be set to zero.
3.
Expose the logger to three known temperatures
For 0°C, put the logger in a watertight bag and place in ice water bath. Alternatively,
Copyright © 2010 ACR Systems Inc. All Rights Reserved.
SmartReader Plus Data Logger
74
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