3.4.2. Density
Measurement by Other Methods Portable Digital Density Meters (Densitometers) There
are other methods to measure density, such as densitometers. Density
measurement must be conducted with a test method listed in [ASTM
D1655] .
3.4.2.1 Description This type of equipment provides an alternative field method
that is easily calibrated and does not pose the hazard of hydrometer glass
breakage present in current field methods. Portable digital density measure the
density and temperature of the filled-in sample at the sample temperature.
The portable digital density meters shall comply
with ASTM D7777/IP 559 Standards
For portable digital density meters with build in
software the measured density and temperature are automatically converted into:
API gravity 15 °C / API gravity 60 °F
Density at 15 °C / density at 60 °F
Relative density 15 °C ⁄15 °C / relative density 60 °F
⁄60 °F
by the instrument using the calculation routines for
Generalized Products as defined in Guide ASTM D1250. Therefore, there is no use of
Conversion Tables or any other means of calculating the density/gravity at
referenced temperature (corrected)
For portable digital density meters without build in
software, read and record the density or
the gravity of the test portion and the indicated test temperature, which needs
to be corrected for reference temperature (60 °F/15 °C).
The instruments are capable, once calibrated,
of determining density with an accuracy of 1 kg ⁄m3, fitted with a temperature
sensing device capable of measuring temperatures to 6 0.5 °C, a pump mechanism for filling and emptying the
U-tube and a digital display of the results. Some density meters have in-built
software for calculating the density at 15 °C from the observed density at test
temperature. Some density meters have a mechanism for adjusting the meter
during calibration; for others, this adjustment is carried out using the
in-built software. The meter may also have a memory for
storing results, or a facility for connecting the meter to either a printer or
a computer, or both.
Portable digital density meters shall be
verified for accuracy every 6 months and calibrated every year. Refer to
2.1.12- Tool Calibration.
3.4.2.2 Procedure
(Ref D7777/IP 559)
Follow manufacturer’s instructions on the
use and handling of the equipment.
1. Make
sure that the portable digital density meter is in thermal equilibrium with the
ambient temperature: If the instrument has been transferred from a much warmer
or much colder place immediately before use, wait for several minutes before
measuring. Do not transfer the instrument frequently between places with very
different ambient temperatures, as humidity condensations may cause measuring
errors.
2. Make
sure to have the samples at or above ambient temperature. Do not fill samples
which are much colder (5 °C ⁄9 °F) than the ambient temperature. This may
generate humidity condensation on the oscillating U-tube sensor, causing incorrect
measurements and potentially harming the instrument.
3. Follow
the manufacturer’s instructions for filling samples into the instrument. If the
sampling system of the portable density meter is not completely free of liquid,
drain it first as much as possible. Then fill a first portion of the sample and
drain it immediately. Then fill the sample portion to be measured. Fill the samples gently.
4. E nsure that gas bubbles are not present in the
oscillating U-tube sensor once filling is completed. If gas bubbles are present
in the oscillating U-tube sensor, drain this sample and gently refill with a
new sample.
5. After
the measurement is finished, drain the sample as much as possible.
6. If
samples of similar composition are to be measured immediately after, rinse the
U-tube by filling and emptying U-tube with the sample at least three times.
7. Report
the final result as:
API gravity to the nearest 0.1 API gravity.
Density at 60
°F to the nearest 1 kg ⁄m3
Relative Density 60 °F ⁄60 °F
to the nearest 0.001 g ⁄cm3,
3.4.2.3 Cautions 1. The portable digital density meters test method shall not be used to determine density for custody transfer quantity calculations, particularly where mass or weight is the unit of quantity measurement.
2. If
the instrument is not being used for extended periods of time, ensure there is
no residue in the u-tube by rinsing multiple times with fuel or a proper
solvent. Follow the manufacturer’s instructions and ASTM D7777/IP 559 for
further cleaning procedures and recommendations for cleaning solvents.
3.If density meter is to be placed in storage the
cell should be cleaned and made dry.
4. Ensure
that the meter's battery is fully charged or replaced if necessary, as low
battery levels can affect accuracy.
5. .Regularly
inspect the meter for any physical damage or wear and tear that could affect
its performance.
6. Check
for any firmware or software updates from the manufacturer that might improve
the meter's performance or accuracy.