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Technology overview

Magnetic inductive technology

Operating according to Faraday's law of induction, when a conductive medium flows through a magnetic field, a voltage proportional to the flow velocity/volumetric quantity is generated.

The voltage is tapped via electrodes and converted in the evaluation electronics to a usable control signal.

Magmeters are great for:

  • Flow measurement of liquids with at least 5% water in line sizes up to 2”
  • Totalized volume
  • Cooling circuits

They should be avoided when:

  • System pressure is above 232 psi
  • The liquid is non-conductive (i.e. oils, deionized water)

Vortex technology

The vortex flow principle is a proven method for measuring flow of water based liquids. Behind a blunt body integrated in a measuring pipe, the flowing liquid generates vortices that are detected by a piezoceramic sensor. Since the cross-section of the pipe is known, the number of vortices determines the flow rate, independent of the liquid's pressure and temperature fluctuations. This technology enables a simple, low cost and easily manufactured flow meter.

Operating principle

Vortex flow meters are great for:

  • Low cost flow measurements of 95% water based liquids
  • Cooling circuits

They should be avoided when:

  • Vibration is present to interfere with the formation of vortices
  • Long straight pipe runs are not available, especially before and after valves and changes in pipe diameter

Thermal technology

Thermal flow sensing technology relies on the cooling effect of flowing liquids, including gases. A higher flow velocity results in a greater cooling effect and this can be reliably measured. The images below depict heat being conducted from the sensor tip by a flowing liquid.

Diagram showing the heat transfer away from the sensing element as media flows by it

For the SA and SI family, two platinum RTD elements and a heater are in the sensor tip. The reference element monitors the temperature of the medium and it is located 10 - 15 mm from the bottom of the tip.  The difference in temperture between the two RTDs is held constant (4 °C) by varying the amount of power applied to the heater. The power required to maintain the temperature difference is directly proportional to the flow rate.

For compressed air applications, the SD design also uses thermal technology. In this case one ceramic probe is heated (the measuring resistor) and the other is not (reference resistor). Flow velocity is determined by the voltage difference between the two resistors when the flow dissipates the heat.

Thermal sensors are great for:

  • Simple switching in pump run-dry protection
  • Rough monitoring of flow of any medium in large pipes
  • Compressed air leak detection

They should be avoided when:

  • Medium temperature changes rapidly
  • High accuracy is required

Mechatronic technology

The SB Mechatronic flow meter works on the principle of a spring supported piston. Flowing liquids lift the piston and the postion of the piston is monitored by a magnetic sensor. The spring forces the piston to it's original positon with decreasing flow and the built-in check valve prevents back flow.

Diagram explaining flow sensor with mechatronic technology for measuring media flowing by the sensor

This design means the meter can be installed without regard to inlet/outlet piping requirements. Because a magnetic sensor is detecting the piston positon, response time is ≤ 10 msec. Since flow is typically relatively stable, there is very little flexing of the spring. The meter has been successully tested to 10 million cycles without any detectable wear.

Mechatronic sensors are great for:

  • Flow circuits requiring very fast response time
  • Installation in tight spaces

They should be avoided when:

  • Medium viscosity is very high

Ultrasonic technology

Ultrasonic sensors consist of transducers that transmit and receive sound pulses and reflectors that direct the pulses from one transducer to the other. A pulse is sent through the medium and the sensor measures the time of flight from one transducer to the other. Then a pulse is sent in the opposite direction. The meter measures the difference in time and calculates the flow rate.

The speed of sound varies in air, oil and water. The sound signal is filtered via a medium selection on the meter so that only the expected time of flight is evaluated. If medium selection is not correct, the meter will display an error. For example, if the medium selection is water but there are air bubbles or turbulence in the pipe, the time of flight measurement will not match that for water and an error will occur.

Ultrasonic sensors are great for:

  • Flow measurement of nonconductive media like oils and deionized water
  • Totalized volume of flow
  • Cooling circuits
  • Lubrication processes

They should be avoided when:

  • Air bubbles are present