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How the PMS bolt load cell works
The BoltSafe bolt load cell is a load cell (load sensor) that is specifically designed to monitor the actual bolt load in bolted joints. PMS stands for Periodic Monitoring System, which allows for monitoring the bolt load at any given time provided that the handheld reader and a probe are used. The PMS load sensors have a non-contacting interface and do not require a cable connection. During service, the unit is powered over an inductive interface connected to a handheld instrument. The bolt load can be monitored directly on the handheld reader using a probe. Using a BoltSafe load cell eliminates any uncertainties about the bolt load. This gives the structure enhanced safety and control and makes the joints more dependable. Besides the safety benefits, there is also a cost reduction during installation and throughout the joint’s service life.
Each sensor utilizes an ASIC (Application Specific Integrated Circuit), which takes care of all signal conditioning and digital communication. Therefore, each BoltSafe load cell has a unique serial number so that it can be individually identified and traced. The digital monitoring system is not only capable of measuring the bolt load, but can also monitor the sensor temperature. The load cell is available in two kinds of steel: our regular stainless steel, and a stronger version that can withstand 15% more load while keeping the same compact dimensions.
Another application of the load cells is in temporary construction or for Structural Health Monitoring. In this case the sensors are used as washers to check the load in the construction to prevent the (temporary) construction from collapsing.
How the PMS bolt load cell is used
Our load cell is used and shaped as a regular washer and is available in sizes M30 to M64 and 1-1/4” to 2-1/2”. The BoltSafe bolt load sensor is placed on the non-driven side of a bolted connection, preferably under a nut. While tightening the bolt, force is being applied to the load washer, which will result in minor deformation of the stainless steel washer. The sensor constantly measures changes in electrical resistance caused by these deformations. This data is used to determine the bolt load at any given moment.
Because the design of our load cells is so rugged, they are able to withstand harsh conditions, such as heavy industrial environments. The load sensors can be used in contact with oil, rain, seawater, ice and temperatures up to 80 degrees Celsius. Using the washers in conditions where the temperature is above 80 or below -40 degrees Celsius is not recommended.
After the one-time calibration of the sensor by BoltSafe, there is no need for recalibration of the load cells in their service life – not even when different readout methods are used – provided they are used according to their specifications and requirements.
Contact us for more information or to order our PMS bolt load cells
Benefits of a periodic monitoring load sensor
BoltSafe PMS load cells can be used in small spaces where cables do not fit. Narrow spaces are the specialty of the PMS washer, because it doesn’t require a cable connection. The PMS bolt load cells can be read without any cable connections using a probe. The user can monitor the actual bolt load directly on the handheld reader. Because of this, it is easy to quickly readout multiple sensors with the same reader one after the other. The data from 256 different load cells can be stored onto the handheld reader. The data can be transferred from the handheld reader to a computer.
Usage in small spaces
Wireless load cell
Quick readout
Readout methods that are compatible with the PMS bolt load sensor
The PMS load cell can be read only by the handheld reader SM-200, in combination with a PMS probe. The probe touches the sensor and data is acquired through infrared. This probe energizes the BoltSafe load cell (which is not battery powered) and reads all data through the non-contacting interface. The probe is in turn connected to the SM-200 handheld reader with a connector. If you connect the handheld reader to a PC with a USB cable, you can transfer the measured bolt load data to a PC with the “Report Generator” software.