Parr Instrument 6400, Руководство по эксплуатации

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6
Standardizations
P a r r I n s t r u m e n t C o m p a n y
48
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haPter
6
Standardizations
Standardizing the Calorimeter
The Energy Equivalent Factor
The term “standardization”, as used here, denotes
the operation of the calorimeter on a standard
sample from which the energy equivalent or effec-
tive heat capacity of the system can be determined.
The energy equivalent, W or EE of the calorimeter
is the energy required to raise the temperature one
degree, usually expressed as calories per degree
Celsius. Standardization tests should be repeated
after changing any parts of the calorimeter, and
occasionally as a check on both the calorimeter and
operating technique.
Standardization Procedure
The procedure for a standardization test is exactly
the same as for testing a fuel sample. Use a pellet
of calorific grade benzoic acid weighing not less
than 0.9 nor more than 1.1 grams. The corrected
temperature rise, T, is determined from the observed
test data and the bomb washings are titrated to
determine the nitric acid correction. The energy
equivalent is computed by substituting the follow-
ing equation:
W =
Hm + e1 + e2 + e3
T
Where:
W
= Energy equivalent of the calorimeter in
calories per °C.
H = Heat of combustion of the standard
benzoic acid sample in calories per
gram.
m = Mass of the sample.
T = Temperature rise in °C.
e
1
= Correction for heat of formation of
nitric acid in calories. The default value
in the 6400 is 8.
e
2
= Correction for sulfur which is usually 0.
e
3
= Correction for heating wire and com-
bustion of cotton thread. The default
value in the 6400 is 50 cal.
Standard Materials
A bottle of 100 one-gram benzoic acid pellets (Part
No. 3415) is furnished with each calorimeter for
standardizing purposes. The Parr benzoic acid has
been calibrated against NIST benzoic acid. Addition-
al benzoic acid pellets can be obtained from Parr.
For very high precision measurements, a primary
standard benzoic acid powder can be purchased
from the National Institute of Standards & Technol-
ogy, Washington, D.C.
It is not common to have sulfur in standard materi-
als, or to use spikes in standardizations, but the
capabilities have been included in this calorimeter.
Users should take great care to ensure that the
conditions during standardization runs and determi-
nations are as identical as possible.
Caution!
Benzoic acid must always be compressed
into a pellet before it is burned in an oxygen
bomb to avoid possible damage from rapid
combustion of the loose powder. This is best
accomplished by using a Parr 2811 Pellet Press.
Automatic Statistical Calculations
The 6400 Calorimeter includes a provision for
calculating and using a mean energy equivalent for
each of up to 4 separate bomb and bucket combina-
tions. ASTM procedures recommend that the energy
equivalent be determined by averaging ten tests.
The 6400 Calorimeter automatically determines and
uses up to ten tests in its memory and will update
the EE Value as additional standardizations are run.
Only Final Tests will be used in determining and
updating EE values. These values, the number of
tests, and the relative standard deviation for the
tests used in determining the EE value are stored
in the Calibration Data Page under the EE Value for
each bomb.
The user can chose to turn off the automatic aver-
aging and updating procedure and protect the EE
Values by turning ON the protection feature for
the appropriate bomb on the Calibration Data and
Control Page using Protected EE Value.