KNOWLEDGE Load cells
Load cells are a critical safety device and necessary in any situation where the weight of an item being lifted is not known, or there is a risk of overloads, writes Martin Halford, managing director at the UK’s Dynamic Load Monitoring, which has a partnership with Chant Engineering Co., of New Britain, Pennsylvania.
load cell is a transducer that is used to measure a force, typically a compressive, tensile or shear force. Most load cells work by using foil strain gauges bonded to a metal structure, designed to perform accurately and safely withstand the load applied to it. The strain gauges measure strain in the load cell material under load and translate that strain to a millivolt (mV) output, which is then typically fed into a display and scaled to a load range – say, pounds or tonnes. Like any sector, the load cell industry has evolved rapidly in recent years, most appreciably in terms of technology. digital handheld displays have been used to read the load for a long time, but electronics built into the load cells can now also transmit the load signal wirelessly to a display or direct to a smartphone or PC using a dongle or Bluetooth. Data-logging software can even be used to log the load data on a PC against time and be analysed and processed at a later date.
A
g
f Martin Halford, managing director of Dynamic Load Monitoring.
Calibration counts You can’t talk about force measurement, in lifting or any other industry, without referencing calibration, which is the correlation of the readings of an instrument to check accuracy. Dealers and end users alike should note that a certificate of calibration is valid for one year; we contact customers when their products are due for recalibration, but it is worth everyone in a supply chain keeping on top of this.
Load cells are calibrated upon their manufacture. Typically, the process
is to take a test machine (in-house) or tensile link (on site) as the reference load cell, which provides a known reading; when the tensile link or machine shows 10t, for example, the other product is referenced to it. Recalibration is especially important because there are many ways to damage a load cell without generating a hazardous incident. It is just as much about asset integrity as safety; the only way to do this is to accurately know the load being applied.
While important, the process is simple: 1. Visually and functionally inspect the equipment; 2. Apply load to the device, with a known reference; 3. Record the load readings from the device before any adjustment is made; 4. Adjust the load output to bring the output within the specified limits (the limit varies depending on the product/application);
5. Produce a calibration certificate to evidence accuracy.
Remember, calibration is the correlation of the readings of an instrument to check accuracy. And accuracy equals safety.
www.ochmagazine.com | Winter 2023 | 29
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