|This measuring system is based on the Faraday’s law: Inside an electrical conductor which moves in a magnetic field, an electrostatic field is created. This electrostatic field can be measured through the voltage between the conductors – a voltage is induced. |
The conductive liquid to be measured correlates with the movement of the conductor. A magnetic field is induced through two current-carrying exciting coils with a constant strength of current.
The voltage generated through the flow of the measurement substance is tapped with two meter electrodes mounted on the inside of the tube. The rate of flow is proportional to the induced voltage which is converted into standard signals with the appropriate transmitter.
|The ultrasonic flow measurement can be divided into the following four principles of measurement:|
1.) Run Time Principle
2.) Doppler Principle
3.) Drift Method
The stroboscopic measurement method works (similar to the Doppler principle) with reflecting ultrasonic signals of moving particles. But as opposed to the Doppler principle, it’s not the frequency shifts which are used, but rather, the time a particle needs to roll a predefined distance in an area of sound is measured. Short ultrasonic impulses in quick succession – similar to strobe light – are radiated.
|The so-called Coriolis principle for mass flow measurement uses Coriolis forces. Those are apparent forces which take hold of moving masses in a rotating reference system. If a moving mass is now exposed to a vibration perpendicular to the direction of movement, then coriolis forces occur (depending on the mass flow).|
The coriolis mass flow measuring units consist of one or two meter tubes which can be stimulated with a resonance frequency of 80 – 1000 Hz. If a medium (= mass) now flows through these oscillating meter tubes, coriolis forces are generated.
These forces change the vibrations by a small amount. The interaction of the coriolis forces and the resonance frequency leads to a minor phase shift, which is registered by the measuring system by means of optical or inductive sensors. The phase shift is a measurement for the mass flow.
In addition to the mass flow, the density of the medium can be determined from the resonance frequency at the same time. To compensate for temperature dependencies, the temperature of the meter tube and thus the temperature of the medium is also registered.
In this way, the measurement converter of the coriolis mass flow measuring unit delivers the three measurements, mass flow, medium density and medium temperature.
|The vortex meter uses the swirl which is generated by an impediment in a flowing medium.|
In the meter tube, the flow of a medium is directed towards a sharp-edged impediment. Behind this impediment, vortexes form regularly on alternating sides due to the interruption of the flow on the sharp edges. A Karmann vortex path develops.
The frequency of the shredding of vortices on both sides of the impediment is proportional to the average flow rate of the medium and thus to the volume flow rate.
The removed vortices create a localized vacuum in the medium and thus in the meter tube. This vacuum is registered by a capacitive sensor and transmitted to the electronics as a primary digital, linear signal.
The measurement signal is not subject to drift. Therefore, vortex meters can be used throughout their lifetime without needing recalibration.
In capacitive sensors with integrated temperature measurement, the mass flow rate of saturated steam can also be measured, for example.
The calorimetric measuring procedure is based on the physics of heat dissipation, i.e. a body with a temperature higher than its surroundings supplies a medium (liquids or gases) flowing past that body with energy in the form of heat.
The amount energy supplied is a function of temperature difference Δt and mass flow. This thermal measurement principle operates on the following method:
The calorimetric measurement procedure is applicable to measure the volume and mass flow as a flow meter or as a flow monitor. The measurement dynamic is > 1:100. the advantage of this principle is the independency of the viscosity and electrical conductivity of the medium to be measured. The small and robust design of the sensor is applicable for all nominal width of pipes.