Why are vibrating wire sensors used in structural and geotechnical monitoring?

Vibrating wire sensors have been around for decades and are respected and used across many areas of the civil and structural engineering industry.

But for those less familiar with geotechnical instrumentation, you may be asking: what are they? How do they work? And, why are they used?

So, we’ve broken down everything you need to know about vibrating wire sensors and how they can provide better benefits than standard electronic sensors.

What are vibrating wire sensors?

A vibrating wire is a sensor that measures the surrounding forces and environmental properties when placed in the ground.

Vibrating wire sensors are used to monitor and record a multitude of parameters, such as:

• Pressure
• StrainLoad
• Displacement
• Settlement
• Temperature

Interestingly, vibrating wire sensors are seen as complex sensors but they are in fact some of the simplest, giving them significant benefits over other electronic sensors.

How do they work?

A vibrating wire consists of a piece of thin metallic wire held at tension between two fixed points.

Once activated, the wire naturally vibrates at it’s resonate frequency. This frequency is then measured.

As tension and force on the wire changes, the vibration frequency either increase or decreases. Via a calibration, this frequency can then be equated to any of the aforementioned parameters.

Here at Geosense, our vibrating wire sensors and instrumentation use a proprietary GeoSwage production process to ensure higher accuracy readings and better long-term reliability.

So, why should I use vibrating wire sensors?

The data acquired from a vibrating wire is highly valuable for clients who are undergoing ground investigation for structural integrity, environmental research, demanding engineering projects and more.

But what are the benefits of using a vibrating wire instead of an electronic sensor?

1. Zero Drift

Vibrating wire sensors are classed as electro-mechanical sensors as they do not contain any electronics. This means they are a simpler sensor offering greater reliability and integrity.

Due to their relatively simple design, they are classed as “zero drift” sensors. This simply means that reading a sensor on day 1, versus year 50, will not show any drift and any change in reading is due to the parameters you are monitoring – this is especially important for long term-trends.

This is important for long term monitoring of large structures such as dams which have a design life of 50+ years.

2. Low Power

Another reason for using vibrating wire sensors is their low power requirement.

As vibrating wire sensors are typically used on site where power may be difficult to access, having the option of reading the sensors via battery power can be very convenient.

Their low power consumption also means that data acquisition systems can be more cost-effective to run and have longer lasting battery lives – perfect for remote monitoring!

3. Robust

Construction sites can be unforgiving environments and any equipment used must be durable and robust.

The simplicity of a vibrating wire sensor makes them a lot less susceptible to mechanical damage than other sensors. As they don’t require on board power or processing, there are fewer factors and risks that could go wrong when the system is installed.

Furthermore, all vibrating wire sensors are designed to be fully sealed against water ingress, meaning the wire and coils will work even when fully submersed in water.

Our sensors at Geosense have all been designed and tested to extremely high levels of ingress protection, ensuring they’re damage resistant and robust.

4. Cable Lengths

As vibrating wire sensors provide a frequency (not a current or resistance), their calibration is not affected by cable lengths. Instances of cables being used for distances up to 3km have been reported. As such, users can benefit from a high level of flexibility on site with the option to increase or decrease the cable length if it were required.

5. Dynamic measurements

Historically, the requirement for dynamic readings pushed the industry towards electronic sensors. Although these allowed for more dynamic readings, they simply didn’t have all the benefits that you can expect from a vibrating sensor.

However, in recent years our friends at Campbell Scientific have developed their CDM dynamic vibrating wire systems to record readings of up to 300 times a second!

Unlock the full potential from geotechnical monitoring solutions

As leading specials in vibrating wire and MEM sensors, our innovative instruments are used in over 80 countries to monitor the behaviour of ground and structural conditions.

With Geosense, our clients have been able to monitor subterranean water levels and pressure for environments such as tunnels and metros, deep foundations, infrastructure projects, mines, geohazards and more.

For more information of our structural and geotechnical monitoring solutions, visit: https://www.geosense.com/