Mesalabs Definer 220 Series, Руководство пользователя

Страница: 27 / 28

25
25
taking measurements. If this is not possible, we recommend disconnecting your Definer
from its AC power adapter/charger while taking flow measurements – or to run gas through
your Definer for 10 minutes before starting the flow measurement.
Why doesn’t my piston return to the bottom of the cell?
If the piston fails to return to the bottom of the cell after a measurement this could be
caused by:
• A discharged battery not providing enough power to operate the internal valve properly
(Try charging the Definer)
• Bright light shining into the unit resulting in an overload of the internal optical sensors
(Try to operate the unit in a shaded location)
• Moisture or dirt inside the cell (Return the Definer to Mesa for service)
What is Dead Volume?
Dead Volume is the gas volume between a flow generator and the instrument taking the
measurement. Since gas is compressible, this gas can act as a spring between the flow
source and the measurement instrument. For best accuracy this volume should be kept to a
minimum.
We recommend keeping the tubing length between the gas flow generator and your Definer
to no more then .5 meters/20 inches in length.
What is Sensor Factor?
Sensor Factor is a number that multiplies the measured flow to scale the reading for cer-
tain types of calibrations. It allows customers to scale a mass flow controller or meter when
calibrated with alternate gases. Care should be exercised to always verify that the scaling
factor is set correctly and we recommend always returning the scaling factor to 1.000 after
completeing a calibration.
What is the difference between volumetric flow and standardized
flow?
As we know from the ideal gas law, the volume of a gas changes with a change in tempera-
ture or pressure even when the number of molecules which constitute the mass remains
the same. Volumetric flow rate is the rate at which a volume of a gas travels past a given
location.
Volumetric Flow = As Measured Volume of Gas / Time
Standardized (mass) flow rate is expressed as the rate at which the volume of a gas travels
past a given location if the gas is at a specified temperature and pressure. From the ideal
gas law if the temperature and pressure are held constant, the volume of the gas is propor-
tional to the number of molecules.
Standardized Flow = Volume of Gas (at the stan -
dard temperature and pressure) / Time
10.0