References
One company, two technologies
SDT's expertise has made it the undisputed leader in ultrasonic detection and measurement in a number of applications in industrial predictive maintenance. SDT is determined to provide effective and preventive solutions to its customers' needs offering them a huge part of added value. This determination also motivated SDT to develop a particularly powerful Air Mass Flow sensor for tightness testing in quality control and for leak quantification in leak detection programs.
Ultrasonic Technology
Ultrasonic technology provides the most precise solution in countless applications: tightness, leaks, electrical discharge and mechanical movement.
The sound solution
Technically, ultrasounds are sounds that cannot be heard by the human ear. In other words, sounds with a frequency above 20 kHz. Ultrasounds have a number of specific characteristics that make them useful in industrial applications.
Ultrasounds can be very precisely measured. Differences in intensity as the waves travel through a medium or body can be quantified. So various phenomena that can influence the working and quality of machines and systems adversely can be clearly identified - often without interrupting their operation.
High frequency sounds are also more directional than lower frequency. This makes it easier to pinpoint the source even in the presence of other background noise.
The other major benefit of ultrasounds is the sheer number of things that produce them. Leaks, stress, electrical discharges, cavitation (the appearance of cavities filled with damp and gas) in flowing liquids, turbulence in flowing gas or liquids; each emits ultrasounds that can be detected and measured.
Precise measurements
Ultrasonic detection and measurement can often be carried out relatively simply. The basic set-up in control situations consists of a hand-held unit with headphones, a meter, a sensitivity adjustment and one of a number of nozzles or modules. Some applications also require a transmitter.
In production facilities, a number of control points can be set up to run automatically. The results of each point are compared with a fixed parameter, and any unusual results are signalled. The equipment can also be connected to a computer system.
The result is rapid, reliable and traceable testing in any number of applications.
Mass flow tightness control
The tighness of a volume
The measure of the tightness of a volume is the measure of the quantity of fluid or gas entering or exiting the volume to be tested when there is a difference of pressure between the exterior and the interior of this volume. One of these two pressures can be equal to atmospheric pressure.
Operation of the mass flow sensor (or MFL)
The principle of the mass flow sensor is based on the transfer of heat created by the flow rate of gas passing over the surface of the sensitive element. The sensor is made up of a heat source and two temperature sensors mounted inside a tube through which the gas passes.
In the absence of a rate of gas flow, the two temperature sensors are heated in the same way; the difference in temperature between these two sensors is therefore nil.
In the presence of a flow of gas, The one sensor is cooled whereas the temperature of the other sensor increases. A difference in temperature proportional to the flow of gas though the sensor is observed between the two thermosensitive resistors. The higher the flow rate of the gas, the greater the difference in temperature. Moreover, the positioning of the sensors (one heat source between two temperature sensors) determines the direction of the flow of gas.