Cracks are among the most common defects in civil engineering structures. Whether they are shrinkage cracks in concrete bridges, deformation cracks in tunnel linings, or wall cracks caused by foundation settlement, the changes in crack width and displacement directly reflect the structural stress state and safety level. Therefore, crack displacement monitoring has become one of the most important parameters in Structural Health Monitoring (SHM).
The KPM12J series miniature articulated displacement sensor (commonly known as crack meter or crack displacement sensor) from Shenzhen Miran Technology Co., Ltd. has gained wide acceptance in crack monitoring applications due to its unique structural design and stable, reliable performance.
1. KPM12J Crack Monitoring Principle
The KPM12J series operates on the potentiometric principle. Inside the sensor, there is a carbon film resistive element and a wiper that moves with the pull rod. When both ends of the sensor are fixed on either side of the crack being measured, any change in crack width causes the sensor's pull rod to extend or retract, moving the wiper across the resistive element. This movement generates a DC voltage signal that is proportional to the displacement.
The raw voltage signal can be converted, via an internal or external V/A transmitter module, into standard industrial signals of 0-5V, 0-10V, or 4-20mA. This enables long-distance transmission to a PLC or data acquisition system, allowing real-time remote monitoring of crack displacement.
2. Core Advantages of KPM12J in Crack Monitoring
2.1 Articulated Joints at Both Ends – Eliminating Installation Stress
The most distinctive structural feature of the KPM12J series is the **articulated (spherical) joints at both ends**. In crack monitoring, the sensor must be installed across the crack, where the two sides may experience in-plane misalignment or slight rotation. Traditional rod-type displacement sensors with rigid connections can be damaged by lateral forces, leading to measurement errors. The KPM12J's articulated joints allow the pull rod to self-align within ±15°, eliminating strict alignment requirements during installation. This ensures that the measured values truly reflect changes in crack width, while also protecting the sensor from damage due to lateral forces.
2.2 High Resolution and Excellent Repeatability
The KPM12J series uses high-precision potentiometric elements, offering infinite resolution and outstanding repeatability, capable of capturing displacement changes at the micron level. This is particularly critical for monitoring the early stages of crack propagation, where early warning often determines the success of subsequent intervention measures.
2.3 Versatility for Various Crack Monitoring Scenarios
Compared to other technologies such as vibrating-wire crack meters or LVDT-based crack gauges, the KPM12J series offers distinct advantages: ease of installation, simple zeroing procedures, and readily usable direct signals. It is suitable for long-term crack monitoring in various concrete structures, including bridges, tunnels, dams, and buildings.
3. Practical Application Case
In a highway bridge crack monitoring project, Miran KPM12J crack meters were installed across web cracks in a prestressed concrete continuous box-girder bridge. The sensors were placed across the cracks, with the articulated joints at both ends fixed to the concrete surface via custom brackets on each side of the crack.
Monitoring data showed that under traffic loads, the crack width fluctuated cyclically with temperature changes, with an amplitude of approximately 0.08mm. These results closely matched finite element analysis predictions. The monitoring point operated continuously for 12 months, with the sensor delivering stable output and showing no zero drift caused by vibration or temperature variations, confirming the reliability of the KPM12J for long-term outdoor monitoring applications.
4. Summary
The Miran KPM12J series miniature articulated displacement sensor, with its potentiometric principle for stable output, articulated joints at both ends to resist lateral forces, and its strengths in high resolution and repeatability, has proven to be a reliable and efficient measurement tool in the field of structural crack monitoring. It provides accurate data support for engineering structural safety assessments.
