5WBB Electromagnetic Flowmeter Empty Pipe Detection and Installation Guide
Many users encounter a common question when using an electromagnetic flowmeter: why does the flowmeter still have a reading when no liquid is passing through the pipe? This is actually closely related to the measuring principle of the electromagnetic flowmeter. This article will explain this phenomenon and introduce the setup method for empty pipe detection and installation precautions.
Working Principle of the Electromagnetic Flowmeter
According to Faraday's law of electromagnetic induction, a conductor moving in a magnetic field generates an induced voltage. In electromagnetic measurement, the flowing medium acts as a moving conductor, and the induced voltage is proportional to the medium flow velocity and is applied to the amplifier through two measuring electrodes. The volumetric flow rate can then be calculated based on the cross-sectional area of the pipe.
Switched DC electricity with alternating polarity generates a direct current (DC) magnetic field. Because measurement depends on the electromagnetic field, even if there is no liquid in the pipe, as long as the magnetic field exists, the flowmeter may still output a reading. The schematic diagram of the principle is as follows:
How to Enable the Empty Pipe Detection Function
Due to the limitations of the measuring principle, readings when there is no liquid are unavoidable. In this case, the empty pipe detection (EPD) function can be enabled. Once enabled, the flowmeter will output an error current when there is no liquid; if not enabled, it will output a flow reading.
Setup Steps
- Enter group selection and select measured value.
- Select process parameters and turn on the empty pipe detection function.
- Enter access password 10.
- Change OFF to ON, and empty pipe detection is enabled.
The setup interface is shown in the figure:
Installation Precautions
When installing the device, it must be carried out strictly in accordance with the manual requirements to ensure measurement accuracy and long-term stability.
Pipe Position and Direction
- It is strictly prohibited to install it at the highest point of the pipe (prone to gas accumulation) or directly above a downward-draining pipe, to prevent gas accumulation or bubbles from increasing errors.
- When installing on a horizontal pipe, the measuring electrode axis must remain horizontal to avoid bubbles causing brief insulation between the two electrodes.
- Non-full pipes installed at an incline need a vent, and the sensor must not be installed at the lowest point of an inclined pipe (to prevent solid accumulation); it is recommended to install a drain valve.
Conditions for Using Empty Pipe Detection (EPD)
The empty pipe detection function can detect empty pipes or non-full pipes and improve safety, but it can work properly only when the pipe is horizontal and the transmitter head is facing upward.
Vertical Pipe Installation
When installing on a vertically downward pipe with a height of >=5 m (16.4 ft), a siphon or drain valve must be installed in the downstream pipe of the sensor to prevent suction pressure from damaging the measuring tube liner. A vertical pipe is the ideal installation direction for self-draining piping systems and systems with empty pipe detection.
Vibration Environment and Straight Pipe Section Requirements
- If used in an environment with severe vibration, the piping system and sensor must be reinforced to avoid vibration affecting measurement stability.
- The sensor installation position must be away from valves, tees, and elbow fittings, ensuring the upstream straight pipe section length is >=5 x DN and the downstream straight pipe section length is >=2 x DN to meet measurement accuracy.
Large-Diameter Pipe Installation
When the sensor is installed on a large-diameter pipe, an adapter pipe (double-flange reducer) conforming to the DINEN545 standard can be selected. Especially when measuring fluids with extremely slow flow velocity, it can increase the flow velocity and improve accuracy. Before use, refer to the diagram to calculate the system pressure loss caused by the reducer or expander.