The Air Monitor multi-point self-averaging pitot averaging technology is unique in that it is a pure instrument measuring true velocity pressure (total pressure – true static pressure). Other technologies measure a reference pressure on the back or side of the probe resulting in a DP that is not true velocity pressure as derived from Bernoulli’s Equation. This reference pressure requires the use of correction factors that vary with Reynolds number (i.e. velocity and density changes) in order to relate the measured DP to true velocity pressure. The Air Monitor system also utilizes the Fechheimer method of true static pressure measurement along with a chamfered impact or total pressure measurement to provide an accurate velocity pressure measurement and do so with pitch and yaw angles up to ± 30 degrees without requiring additional corrections.
Differential Pressure technology is commonly used to measure fluid velocity due to their well-defined relationship. The square root of the differential pressure is proportional to the velocity of the fluid. In ducted systems the total pressure consists of the velocity pressure and static pressure. By measuring the total and static pressures in a duct, the velocity pressure can be obtained by subtracting static pressure from total pressure. This is achieved in practice by directly measuring the differential pressure between the two. Airflow measurement over a large velocity range requires an extensive selection of DP transducers with multiple upper range limits (URLs) to fit the required application – from ultra-low range like 0.05” w.c. URL transducer and higher. Air monitor offers this ultra-low range DP sensing capability coupled with the Auto-zero function to provide a highly accurate DP measurement with long term calibration stability starting for 0.05” w.c. URL transmitters.
AUTO-zero Function – Advanced Transmitter Technology
Some Air Monitor transmitters are furnished with an automatic zeroing circuit capable of electronically adjusting the transmitter zero at predetermined time intervals while simultaneously holding the transmitter output signal. The automatic zeroing circuit eliminates all output signal drift due to thermal, electronic or mechanical effects, as well as the need for initial or periodic transmitter zeroing. For transmitters operated in temperature controlled spaces (with no thermal effect upon span), this automatic zeroing function essentially produces a “self-calibrating” transmitter. The automatic zeroing circuit will re-zero the transmitter to within 0.1% of its operating span; for a transmitter with a 0.02 IN w.c. operating span, this represents a zeroing capability within 0.00002 IN w.c.
AUTO-purge III Option for Dirty Gas Applications – Install it and forget it
Air Monitor’s AUTO-purge III offers automatic purging at regular field-selectable intervals. AUTO-purge III is designed for applications where the continuous exposure to airborne particulate might impair the measurement accuracy of Air Monitor’s CA (Combustion Airflow) Station or VOLU-probe/SS array. When activated by an Air Monitor smart flow transmitter such as the VELTRON II, MASS-tron II, or VELTRON DPT-plus, or a distributed control system, a combination of valves are operated to introduce high pressure/high volume air into the flow measurement device’s sensing ports for a short duration while simultaneously isolating the transmitter from over pressurization. This periodic purging assists in maintaining the sensing ports of the total and static pressure manifolds in a clear, unobstructed condition.
