Transit Time Measurement With The Doppler Effect

   Flow measurement is an important part of business for many industries and companies.  Whether it is the measurement of a flow of  gas (such as natural gas) or the measurement of liquids, obtaining a precise measurement can be critical to the success of a process.  Ultrasonic flow meters are one way in which these flow measurements can be made.  An ultrasonic flow meter makes use of the physical principle known as the Doppler Effect.

  Simply put, the Doppler shift is the shift in frequency that a sound wave will incur upon bouncing off a substance in motion.  Entrained air bubbles or particles in a liquid flow will reflect an ultrasound beam back to sensors within the ultrasonic flow meter unit.  There the device, often portable in nature, will insert the calculated transit times into various algorithms in order to determine the flow measurement to a certain accuracy level.  In the case of gases, the known transit time of a given flow of gas can be used to determine whether there is more gas flow or less. 

   The advantage of an ultrasonic flow meter is that it is not an invasive measurement tool.  The non-invasive feature means that a mechanic can simply clamp the meter onto the outside of existing pipe without interrupting the flow at all.  Some models of ultrasonic flow meters are meant to be semi-permanently attached in place while others are more portable kits which closely resemble an advanced graphing calculator.  Those can be tossed in a toolkit or work van and taken onsite wherever needed.  More advanced models include features that enable the flow meter to be attached to a laptop computer (or maybe through a wireless internet connection) in order to interface with flow measurement software and monitor multiple points at once. 

Transit time flow meters may need a periodic calibration to make sure the readings remain accurate to the negotiated tolerances.  Generally the manufacturers or third-party companies can service the calibration after a certain number of flow surveys or so many years of use.  Look for ultrasonic flow meters that have a long battery lifetime and provide a power cord for wired usage. 

Ultrasonic flow meters are sold based on the inner diameter of the pipe that will be clamped onto for measurement.  The excellent thing about these meters is that they can survey just about any type of pipe from pvc to copper or even lined piping.  A pipe that is encased in cement will still give useful measurements. 

There is no reason not to have a group of these ultrasonic flowmeters attached at various key points in a factor or other operating environment.  The information feedback that they provide will be valuable beyond the cost of the meter.

Ultrasonic Flow Meters Clamp Onto PipesCredit: image by mementosis on FlickrCredit: image by mementosis on Flickr