Roger Ellis s

8/13/2019 Roger Ellis s

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Major applications

Monitoring water pressure in and out of a

tank.

Pore pressure monitoring on land fills and

tailing dams.

Structural monitoring of strain and/or load.

Any other application that requires amonitoring of pressure, strain, load or water

depth.


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Basic Working Principle

Pressure


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Pressure

Bore holes are drilled into sensor to allow pressure into

main chamber. Usually passing through a filter in order to

rid the system of particles.

Fluids or gases then push on the diaphram Pressures on the diaphragm cause changes on the

tension & frequency of the wire.

Wire is excited by the electromagnetic coils

Changes in these parameters are then transmitted

through the coils to a read out device or a datalogger to

save measurement details


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Sample Configuration 1

Pressure in fluid tank

A vibrating wire piezometer is inserted into a tank.

Calibration is typically not required depending on

model

Once inserted into tank a measurement is taken.

Giving the user the pressure at the bottom of the

tank. Any changes in fluid level will result in a new

measurement shown by the sensor.


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Strain

Figure from:

http://cee.engr.ucdavis.edu/faculty/chai/Research/Benicia%20Martinez/vibrating-wire-strain-gage.jpg


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Strain

Connect across the axis of interest

Usually involves soldering of the sensor to thestructure

Strains to the load or structure will cause theresistive element inside the sensor to expandor contract.

Measuring the total resistance of the elementwill tell the amount of strain the structure orload.


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Sample Configuration 2

Strain

Solder sensor to desired axis of measurement onbridge

Connect sensor to a voltage source as well as adata logger to keep track of the measurementsand data

When load is under stress and experiences a strain

the sensor will interpret that with a change inresistance and thus a change in measurement willoccur.


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Major Specifications

Pressure: different models range from 01000+psi.

Pressure accuracy: 0.1% of full scale output

Temperature: Operating range -40oC to 230oC Extremes not available in a single model

Resolution: 0.025%FS

Filter: 50-micron sintered stainless steel Some models also have ceramic filters

Mass: anywhere from .10kg to 1.5kg


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Major Specifications

Diaphragm displacement: < .001 cm3

Linearity: < 0.5% FS

Sensitivity: 1*10^5 Mpa Thermal Drift: < 0.1% F.S. / C

Input signal, sinusoidal: 150 to 170 mV rms

Output signal, sinusoidal: 10 to 30 mV rms


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Choosing a sensor

What type of material is your vibrating wire senor

going to be located in?

Some environmental factors require the that sensor

have a non-corrosive exterior Higher pressure applications require a stronger

exterior

Sensor data must be transmitted to a source via a

cable. Choosing the cable sheath is also important,

different applications call for different requirements.


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Choosing a sensor

How are you going to extract the data given bythe sensor?

Handheld devices are available to read out the

current data Data loggers are mini computers that are

programmable and can be used to read, process,and save data from the vibrating wire sensors.

These are typically used if you want to monitor asystem for an extended period of time.


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Limitations

High rate of change in pressures (depending onmake and model)

Casingdifferent applications require differenthousing

Various models dont come with a thermistor fortemperature acquisition

Cheaper models cover smaller pressure spectrum

7.5 MPa is highest pressure Ive found Thermal operating rangehigher temps usually

require more expensive models

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