Vibrating wire piezometers are instruments of great reliability and high strength, used for measuring pore and neutral pressures and hydraulic levels. The instrument, consists of a stainless steel cylindrical body with a calibrated stainless steel membrane on top.
Together with the harmonic steel wire and electro-magnetic excitation group, this comprises the transducer element of the instrument. This membrane deflects when subjected to a pressure difference (external/internal), and, as a consequence, variation in stress (and consequent deformation) of the wire, causing a variation in frequency vibration on excitation.
Measurement of this frequency allows calculation of the pressure on the membrane.
A fundamental characteristic of the instrument is the tightness at very high pressures; sealing is assured by complete welding between the external body and the related membrane and by the terminal part of the cable connection where the cable entrance is protected by a disk with metal glass pins which have been properly welded to the instrument body. No O-ring seals are used.
The membrane is protected by a bronze or sintered steel filter, with permeability of 10µ or 30µ, according to the method of installation.
The instrument is equipped with a coil calibrated for the measurement of temperature; as an alternative, on specific request, it can be equipped with an internal thermistor.
These devices are compatible and usable with most dataloggers for vibrating wire on the market.
For manual measurements, we suggest our portable dataloggers DEC3000 or DEC5 and for automatic systems, our dataloggers CUM3000, VW Hub 2 and cRIO Vibrating Wire Modules.
They can be integrated into automatic monitoring systems with real-time monitoring of phenomena and management of local and remote real-time alarms.
Vibrating Wire Piezometer Applications
Vibrating wire piezometers are used for the measurement of pore pressures and hydraulic levels, with the possibility of remote transmission of data.
Used in particular in concrete dams to detect the development of uplift pressures and seepage in foundations. In earth dams, they allow the monitoring of saturation lines in clay cores and evaluation of the efficacy of waterproof diaphragms and drainage filters.
High resolution and reliability, robustness and the choice of a fully welded method instead of O-rings, make these instruments ideal for installation in dams, cemented holes and anywhere difficult or impossible to access for maintenance or replacement of the instrument.
Typical applications are:
- Geotechnical, geological, structural and hydrological monitoring in general
Features and Benefits
- High resolution and sensitivity
- Good speed response of the sensor
- Housing in stainless steel, completely watertight
- Large choice of range (custom designed upon request)
- Use of porous filters in bronze or steel, at different porosity (10 μ or 30 μ, standard)
- Great reliability over time: the ideal instrument for long-term monitoring and installation in not easily accessible or difficult locations
- Absence of drifts
- Reduced vulnerability to overvoltages
Our piezometers are composed by a stainless steel body with calibrated membrane to which the vibrating wire transducer is connected. Pressure causes deformation of the membrane with a corresponding variation in stress on the vibrating wire.
The change in in tension of the wire causes a variation of vibration frequency of the vibrating wire, the square of vibration frequency being directly proportional to the pressure applied to the membrane.
A dedicated excitation group, composed by two coils positioned on an electromagnet, enables the generation of a pulse for vibration of the wire and, at the same time, constitutes the primary element detecting the vibration frequency of the wire.
The connection of the instrument to junction boxes is possible with 2x1smm cable for the measurement of pressure or by 3x1smm or 4x1smm cable for the measurement of pressure and temperature .
The section of the conductors is established according to distance from the final measuring point; we suggest, however, a rubber insulated cable with thick insulation, external diameter 11mm, suitable for direct embedding in concrete and embankments; the suggested section for the conductors is 1mm2.
The cable is locked and protected by a tube with reduced diameter and connected to the instrument body , externally to the metal/glass element of the sealing element.
Additionally it is sealed with resin and a metallic cable gland.
This kind of vibrating wire instruments can be read by our portable readout units DEC5 and DEC3000 or by our automatic acquisition system DAC3000.
Each instrument can be tested and calibrated on a control bench and provided with a calibration certificate complete with gauge factor and zero value taken in our laboratory.
The membrane is protected by a bronze or sintered steel filter, with permeability of 10 μ or 30 μ depending on application. The instrument is equipped with calibrated coil for the measurement of temperature.
As an alternative and on specific request, it can be complete with internal thermistor.
Vibrating Wire Piezometer
|Range (kg/cmq)||3 or 5 or 10 or 15 or 20 or 30 (other ranges upon request)|
|Operation Range (Hz)||500 – 1200|
|Drift in temperature||0,025% f.s. for °C|
|Filter||In bronze or sintered steel, porosity 10μm or 30μm|
|Material||Stainless steel AISI 304|
|Dimensions||35mm x 110mm|
|Membrane sealing||Electrowelding TIG|
|Cable sealing||By weld metal glass, resin and cable sleeve|
|Type||Rubber insulated 2×1 mm2; 3x1mm2|
|Maximum allowable traction||15 N/mm2 movable installations; 50 N/mm2 fixed installation|
|Weight for 100m||3x1mm2: 18Kg
Accessories and related products
|Junction Box||Available in different models for the connection of different instruments|
|Selection and Measurement Box||Complete measurement box with MUX cards for the automatic selection|
|Measurement Box||Simple measurement box|
|Cable 2 x 1 or 3 x 1 mm2||Special cable insulated in santoprene for the piezometer connection (simple or with temperature measurement)|
|Multipolar cable||Available with different conductors to connect different sensors to one cable|
|DEC5||Portable Readout Unit|
|CUM3000||Multichannel – Datalogger|
|MUX||Multiplexer for the connection of different sensors|
If you have any requests or questions about our instruments or if you have special needs that require different solutions from the standard, please contact us. Our team will provide all the necessary information and will be very happy to work with you to study, develop and customize instruments and solutions suitable for your specific needs.
All information in our datasheet is subject to change without prior notice.
Please check the datasheet/details carefully and contact Pizzi Instruments for further information.