Parr Instrument 6772 - Manual (Page 24)

6772
Calorimetric Thermometer Instruction Manual
4-4
Fill the calorimeter bucket by first taring the dry bucket on a solution or trip balance; then add
2000 (± 0.5) grams of water. Distilled water is preferred, but demineralized or tap water
containing less than 250 ppm of dissolved solids is satisfactory. The bucket water
temperature should be approximately 1 - 2 °C below the room temperature. It is not
necessary to use exactly 2000 grams, but the amount selected must be duplicated within ±
0.5 gram for each run. Instead of weighing the bucket, it can be filled from an automatic
pipet, or from any other volumetric device if the repeatability of the filling system is within ±
0.5 ml.
Set the bucket in the calorimeter jacket. Attach the lifting handle to the two holes in the side
of the screw cap and partially lower the bomb in the water. Handle the bomb carefully during
this operation so that the sample will not be disturbed. Push the two ignition lead wires into
the terminal sockets on the bomb head. Orient the wires away from the stirrer shaft so they
do not become tangled in the stirring mechanism. Lower the bomb completely into the water
with its feet spanning the circular boss in the bottom of the bucket. Remove the lifting handle
and shake any drops of water back into the bucket and check for gas bubbles.
Place the calorimeter cover on the calorimeter jacket. This immerses the stirrer and
thermistor probe in the bucket. Ensure that the stirrer motor and ignition leads are connected
to the rear of the 6772 Calorimetric Thermometer.
After the calorimeter is fully assembled with a charged bomb, turn on the motor, and then
turn on the stirrer by pressing the stirrer key on the calorimeter operation menu screen. This
will begin gently circulating the water that surrounds the combustion bomb. Turn on the data
logger (accessed via the Diagnostics page) in order to periodically record the bucket or
calorimeter temperature. This begins the calorimetric pre-period. The bucket temperature is
updated every 10 seconds. The pre-period should last for 6-7 minutes. After the 6-7 minute
pre-period test phase, activate the calorimeter ignition circuit by pressing the activate ignition
button. This will charge the ignition circuit and ignite the sample. This begins the calorimetric
post-period. The calorimeter temperature should begin to significantly rise at this point,
indicating sample combustion. The calorimetric post-period should last for an additional 6-7
minutes. At the conclusion of the post-period, turn the stirrer off by pressing the stirrer key
once again. The motor switch may be left in the “on” position for subsequent tests.
If the data log destination is a log file, the log file is located at /flash/datalog.csv and may be
retrieved via FTP. The log file is easily imported into a spreadsheet program where the
calorimeter temperature can be plotted in order to realize a thermal curve. Instructions for
working with or analyzing thermal curves are found in the calculations section.
At the conclusion of the test, open the cover, remove the bomb and bucket. Remove the
bomb from the bucket and open the knurled valve knob on the bomb head to release the
residual gas pressure before attempting to remove the cap. This release should proceed
slowly over a period of not less than one minute to avoid entrainment losses.
After all pressure has been released, unscrew the cap; lift the head out of the cylinder and
place it on the support stand. Examine the interior of the bomb and the combustion capsule
for soot or other evidence of incomplete combustion. If such evidence is found, the test will
have to be discarded. Wash all interior surfaces of the bomb (including the head assembly