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 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 S02, 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: 03, 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 S02) 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 holding 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.

MODEL S-5000 Programmable Multi-Gas Calibrator