Wireless Ultrasonic Bolt Tension & Preload Monitoring

Wireless Ultrasonic Bolt Preload & Tension Monitoring System

Broadsens wireless ultrasonic sensors make remote bolt preload/load/tension monitoring a reality. The WUT series wireless ultrasonic sensors have battery life up to 10 years or more, which allows for long-term monitoring of preload and tension for bolts and fasteners. The wireless ultrasonic sensors can be easily installed to bolts of structures such as offshore wind turbines, railroads or oil platforms. The wireless sensors are non-intrusive, and can be mounted on any existing bolts or nuts without modifying the mounting mechanism.

WUT series ultrasonic wireless sensors not only can monitor the bolt condition for many years, but also can monitor dynamic loads/tensions of bolts in real time with up to 10Hz sample rate. Even when the sensors monitor bolts in real time, the battery can still last years before replacement. Users can replace the battery easily when the battery level is low . When WUT sensors measure bolt preload/tension at 30 seconds interval in real time, the battery can last 10 years without replacement. This easily makes WUT series sensors the best wireless ultrasonic sensors for both real time and long term bolt preload & tension monitoring.

WUT204 wireless ultrasonic sensor can monitor preloads (tension) of four bolts in parallel. WUT204 comes with two types of probes. BUP4S probe is a single-element probe that is dedicated for bolt preload & tension monitoring. BUP4S has a wide measurement range of 5cm to 50cm (up to 1,00cm without front protection crystal), which makes the sensor applicable to most large bolts in the industry. BUP4D is dual-element probe that has measurement range of 3mm to 60mm, which is ideal for online corrosion monitoring.

The sensors require to be used with Broadsens's edge-computing gateway and BroadUTM software. The software is preinstalled in the gateway, and provided to users free of charge. Users can monitor the bolt tension in real time. Multiple WUT204 sensors can work in parallel. Each gateway supports up to 100 WUT204 sensors depending on the sample rate. For dynamic bolt tension preload monitoring at 10 Hz sample rate, it is recommend to connect up to 30 WUT204 sensors, or 120 bolts for one gateway. Reducing the sample rates allows to connect more sensors to the same gateway.

Broadsens wireless ultrasonic bolt preload/tension sensors also come with data logger ability. Each sensor can save up to 9,200 samples. This feature is useful when the sensors are installed inside a completely sealed Faraday cage, where wireless signal is completely blocked. In this case, the sensors can still continuously monitor the bolt load, and users can download the data to the gateway later on when the cage is open. The log data can be further exported to CSV file.

WUT204 sensor has two models based on enclosure options:

• WUT204-S has screw type enclosure that is made of stainless steel, and allow the sensor to be mounted to screw holes for long-term monitoring. The WUT204-S sensor has four SMA extension cables coming out, which can be connected to BUP4S ultrasonic sensors.
• WUT204-R has regular rectangular enclosure that is made of aerospace grade aluminum alloy, and has four SMA connectors for easy connection. WUT204-R has mounting flanges on both sides, and can be screwed to a structure.

Ultrasonic probes BUP4S or BUP4D can connect to WUT204 sensor easily through SMA connector.

WUT204 sensor also measures structure surface temperature with PT1000 platinum temperature sensor. The temperature sensor helps to compensate for environment temperature effect.

Principles of ultrasonic Bolt Preload Monitoring

Preload is the axial force in the bolt that is introduced by tightening the bolt. A preloaded bolt creates the corresponding clamping force in the joint. A bolted joint will be affected by vibrations, dynamic loads, thermal cycles, corrosions etc. Therefore, maintaining proper preload is critical for the bolted joints functionality.

Ultrasonic measurement provides a precise measure of preload force. An ultrasonic signal is sent down from ultrasonic transducer at the end of the fastener, and the time it takes for the signal to return to the transducer is measured. Based on the time of flight of this ultrasonic signal, the bolt elongation can be determined using a reference measurement (unloaded fastener length). The length change of the bolt can be used to calculate the preload force accurately, hence obtain the amount of tension within the installed bolt.