FURNESS Controls has developed a range of laminar flow devices and differential pressure readouts to allow accurate measurement of gas flow over a wide turn down ratio.
The conventional devices for measuring air and gas volume flow in pipes and ducts rely on non linear elements such as Pitot tubes, annubars or orifice plates, where the differential pressure produces is proportional to the square of the gas velocity.
As a result, a 10 fold reduction in flow rate produces a 100 fold drop in pressure, which is beyond the practical limit of most differential pressure measurements.
Furness Controls have addressed these deficiencies with a range of laminar flow elements, where the DP is proportional to the flow rate over a very wide range.
These devices produce a minimal restriction to flow (typically only 10mm H2O for full scale flow rate), and allow a much wider turn down by virtue of the linear pressure relationship.
In addition, Furness Controls have developed a special pressure measurement technology using stretched metal diaphragms, rather than the corrugated diaphragms used in most low pressure devices.
As a result it is possible to maintain linearity down to zero pressure, and the accuracy is typically specified as a % of reading, rather than % of full scale, as used by most manufacturers.
The combination of these two approaches can permit accurate gas flow measurements over turn down ratios of as much as 1000:1. Unlike systems based on mass flow sensors, the laminar flow elements can operate over a wide range of operating temperatures, while also avoiding the sensitivity of these systems to even tiny amounts of contamination which can change the thermal characteristics.
Technical and Scientific Equipment can supply the full range of Furness Controls equipment for low pressure and flow rate measurement.