donut load cells

A donut load cell’s central hole is the feature that drives its selection for most structural health applications. Instead of attaching a sensor next to a bolt or cable, the annular transducer sits under the nut or bearing plate and measures the force directly along the load path. Kingmach donut load cells start from a machined alloy steel or stainless steel element, depending on the corrosion environment, and are typically instrumented with multiple strain gauges arranged to cancel bending moments—so you get a clean axial reading even if the bearing surfaces aren’t perfectly parallel. Capacities can be built to suit everything from small ground anchors up to multi-strand stay cables, and the inner diameter can be sized to clear standard coarse-thread bolts or custom tendon profiles. Because many monitoring sites are remote, our standard units are temperature-compensated from about -10 °C to 50 °C, and we can adjust the compensation range for extreme climates. Signal output is normally millivolt per volt, matching most data loggers used in geotechnical work, but we can integrate amplifiers for 4-20 mA or voltage outputs when needed. Each load cell ships with a calibration certificate traceable to a recognized standard, and we maintain records by serial number so that replacement or calibration history is easy to retrieve. Kingmach’s global distribution network means you can get technical support and spares without long lead times, whether the project is in Southeast Asia, Europe, or the Americas. For one-off installations, our application engineers can help work through the mounting geometry and recommend a wiring scheme that minimizes noise. For larger programs—say, a tunneling contractor with dozens of rock bolts to instrument—we can batch-produce with matched sensitivity to simplify data analysis. The donut form factor has been a workhorse in geotechnical monitoring for decades because it solves a physical interference problem cleanly. With the right material selection and sealing, these load cells deliver reliable readings for years underground or in marine environments, and we’ve seen units that come back for recalibration after five years still performing within specification.