Functionality of electromagnetic flow meters

Volumetric measurement based on the induction principle

The measurement principle of the electromagnetic flow sensor is based on Faraday’s law of electromagnetic induction. The air coils integrated in the measurement pipes create a continuous magnetic field (B) orthogonal to the flow direction. The charge carriers of a conductive liquid (Q) are diverted when they pass through the magnetic field, which creates an electric voltage (U). The voltage is proportional to the average flow velocity and is detected by the two electrodes. This means that the higher the flow velocity, the higher the induced voltage. The voltage signal is converted by the integrated electronics of the transmitter into a flow volume based on the nominal width of the pipe.

Structure of the electromagnetic flow meters from Baumer

Electromagnetic flow meters from Baumer consist of a transducer (PF75H/S optionally with a display) and the sensor. The sensor is directly installed in the process, i.e., in the pipe (inline), and measures the induced voltage that is created by the conductive medium while the medium flows through the measurement pipe. The sensor is available for different pipe dimensions and applications.

1) Transducer
2) Optional display
3) Sensor

Display

Key parameters and the menu functions can be shown and configured in the CombiView display of the flow sensor.

How is the display structured?

The display is divided into 3 sections:

1) Status bar

The status bar shows pictograms for alarm and error messages as well as the status of the DFON relays.

2) Main section

Depending on the selected display layout, the following measured values are shown in the main section:

Flow rate
Positive partial counter
Negative partial counter
Net partial counter
Positive overall counter
Negative overall counter
Net overall counter

3) Extra Bar

Depending on the selected display layout, the following measured values are shown in the extra bar:

Label or number tag
Units of the measured values
Graphical display of the flow rate

For more information about the display menu navigation and the available display layouts, see the operating manual of the PF75H/S sensor variants.

Wide selection of measurement pipe linings

The electromagnetic flow sensors from Baumer offer a wide range of measurement pipe linings for every medium. The correct selection of the optimum material depends on the medium, proportion of solids in the medium, process pressure, and process temperature.

Table with recommended materials:

Selecting the appropriate flow meter

The choice of the appropriate flow meter depends not only on the measurement pipe lining but also essentially on the nominal width of the measurement pipe, i.e., the sensor. The nominal width is generally determined by the existing pipeline. With the help of the alignment chart below, you can carry out a control calculation based on the predominant flow velocity of the system.

Baumer offers flow sensors with nominal widths from DN 3 to DN 250.

Deviating values

If there are deviations between the calculated nominal width of the flow sensor and the specified pipe diameter, then the value of the sensor is usually lower. If the constriction angle is less than 8°, it can be adjusted with conical flange adapter pieces. It is essential to take the pressure loss occurring in the system into account. The pressure loss can be found in the overview below at the intersection of the diameter ratio d/D and the flow velocity on the y axis.