Mass
flow measurements, as opposed to volumetric flow measurements, are not
pressure dependent. The air and gas controllers used in the model
S-5000 make use of mass flow to precisely measure and control flow
rates of either clean air or gas cylinders in order to achieve precise
and repeatable gas concentrations.
The “MFC´s” are a combination of a mass flow sensor and a
electronically actuated valve working with the sensors. The valve will
open and close automatically in proportion to the flow required. A
voltage command from the microprocessor is sent to the MFC and de
sensor set up the flow required by that voltage. The voltage output of
the sensor is then translated in the
proper flow units and can be
monitored on the alphanumeric display of the calibrator. The voltage
feedback of the MFC is also used by the microprocessor to more
accurately control the flow.
Dilution of common pollutants such as SO2, NO, CO and CH4, to
user –specified levels occurs through the precise blending of the gas
with clean (or “zero”) air inside of a dilution chamber designated per
EPA specifications.
Performance of Gas Phase Titration for creating NO2 occurs through a
combination of diluting NO gas in the dilution chamber, and reacting it
with
ozone in the reaction chamber. The ozone is created by an ozone
generator (models S-5000 options: O3, Photometer and Permeation)
utilizing a low pressure mercury lamp which produces ultraviolet light
at 185 nanometers wavelength, thus creating ozone in the air flow. The
amount of ozone produced is proportional to the intensity of 184 nm
light, which is dependent on lamp current and temperature. Lamp
temperature is held constant while the lamp current is varied to
produce selected amounts of ozone. Permeation oven
output (typically
NO2 or SO2) is created in the model S-5000 with Permeation by passing
zero air through a temperature-controlled oven containing the desire
permeation device.
Concentrations are varied by precisely controlling the flow rate
through the oven, while hokding the temperature stable. Operation of
the model S-5000 is simple, as desired gas calibration levels and
calibration sequence of events can be programmed into the unit´s memory
and then recalled by selecting the
stored program number; thus, time
spent setting up calibrations on-site is minimized. Such calibration
programs can be easily erased or modified to fit the requirements of
the user.
No calculations need to be executed by the operator since, once
you answer the questions made for the S-5000 about; concentration of
the gas cylinder, flow of the zero air and final output desired
concentration/s, the unit will make the needed calculations and control
the MFC´s to deliver the requested concentrations.
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