A vibrating wire piezometer, or VWP, is a type of piezometer that measures the pore water pressure at a certain elevation by converting the pore water pressure at it’s installation elevation to a frequency which is then recorded and can be converted back into applicable engineering units.
They are very useful for measuring pore water pressures over time, as they can be easily fitted with a data logger. Using a VWP with a data loggers allows groundwater readings to be taken constantly, without the need for someone to be present on site to take the readings.
How Does A Vibrating Wire Piezometer Work?
The name sounds like it would be quite complicated, but it’s actually pretty simple.
Aside from the obvious parts like the housing and anchor cable, a vibrating wire piezometer consists of 3 parts: an electromagnetic coil, the diaphragm, and a tensioned steel wire.
The tensioned steel wire wire is attached to the diaphragm and to a solid part of the housing. Surrounding the tensioned steel wire is a set of electromagnetic coils. When the VWP is installed and turned on, an electric current is passed through the electromagnetic coils which causes a magnetic field to form around the wire, which then causes the wire to vibrate.
The wire will continually vibrate at the same frequency, as the current passing through the coils remains constant. The only thing that can change the frequency of the wire’s vibration, is a change in its tension.
As you may have guessed the diaphragm to which the the tensioned steel wire is attached, moves in accordance to the water pressure.
When the water pressure does change, the diaphragm moves slightly, changing the tension in the wire – causing a change in the frequency of its vibration.
This change in frequency in the wire can then be used to calculate water pressures.
Conclusion
I hope this article helped you understand how VWPs work. If you think you need a VWP for groundwater monitoring in Calgary, please contact us for a free quote.
