What is a Direct Tension Indicator?
A Direct Tension Indicator (DTI) or Tension Washer is a device used to measure the tension or load in a bolted joint. It provides a direct indication of the tension in the bolt, helping to ensure that the correct tension is achieved during the tightening process.
The DTI typically consists of a small circular disc with markings or lines on its surface. It is placed under the head of the bolt or nut, and as the bolt is tightened, the DTI undergoes deformation. The deformation of the Tension Washer indicates the tension in the bolt, and the markings on the disc can be used to determine the applied tension.
The principle behind the DTI is that when a bolt is tightened, it stretches and creates tension in the joint. The DTI is designed to deform in a predictable manner as the bolt tension increases. By measuring the deformation of the DTI, engineers and technicians can determine the tension in the bolt and ensure that it meets the required specifications.
Bolt load cells
Bolt load cells
BoltSafe digital load cells are specially designed to monitor the bolt load in bolted joints. Knowing this information enhances safety, makes joints more dependable and results in better control over bolted constructions.
BoltSafe digital load cells can send their data to different readout methods. We offer the following: the Handheld Reader, Network with PDI, Network with PDI-NT, RS-232 and Analog Converter and the IoT-node.
Direct Tension Indicators vs. Digital Load Sensors
While Direct Tension Indicators can serve as a cost-effective solution for certain applications where high accuracy is not critical, and where visual inspection of tension is sufficient, it should be noted that they do bear some disadvantages in comparison to digital load cells. This is because the technology used in Direct Tension Indicators suffers from a few drawbacks:
- Subjectivity: DTIs rely on visual inspection and interpretation of markings or deformation on the indicator disc. The readings may be subjective and prone to human error. In contrast, digital load cells provide precise digital measurements, eliminating the subjectivity associated with DTIs.
- Limited Accuracy: DTIs have limitations when it comes to accuracy. The markings or lines on the DTI disc may not provide fine-grained measurements, making it challenging to achieve precise tension values. Digital load cells, on the other hand, leverage advanced technology to offer highly accurate and reliable measurements.
- Single-Use: DTIs are typically single-use devices, meaning they need to be replaced after each use. Once the DTI is deformed, it cannot be reset or recalibrated. In contrast, digital load cells can be reused multiple times and often offer the ability to recalibrate or reset for accurate measurements over an extended period.
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How does the BoltSafe digital load cell work?
BoltSafe’s digital load cells are specifically engineered to accurately measure and monitor bolt load in bolted constructions, ensuring superior control, enhanced safety, and reliable joints. These advanced load cells offer a distinct advantage over traditional strain gauge technology used in direct tension indicators.
Unlike strain gauges, which rely on attachment to the material and measuring deformation, BoltSafe’s digital load cells utilize electromagnetic technology. This allows for a significantly more compact construction, eliminating the need for thick sensors that are associated with strain gauges.
When utilizing the BoltSafe digital load cell, the load cell is placed on the non-driven side of a bolted connection, preferably under a nut. As the bolt is tightened, it experiences applied forces, resulting in minor deformations of the stainless steel washer. The digital sensors accurately measure the change in electrical resistance caused by these deformations, providing precise data on the bolt load at any given moment.
BoltSafe’s digital load cells serve a wide range of applications, including Structural Health Monitoring and temporary constructions. These versatile load cells play a vital role in preventing structural collapses by accurately measuring the load on critical elements. Our product line includes load cells designed for continuous and periodic, available in regular and enhanced versions that maintain compact dimensions while withstanding 15% higher loads. Notably, BoltSafe sensors exclusively transmit digital signals, making them the epitome of digital load cell technology.