A compact load cell with RS232 interface
HBK offers the whole measurement chain but LGC Automation was only looking for the weighing sensor. For the processing electronics, it wanted to use its own circuit board which is optimized in terms of price and performance. As for the display and the user interface, they are provided by means of a touch-screen tablet in Bluetooth mode. The choice of the loading cell relates to the PW20i, which is optimized for dynamic weighing applications. This sensor meets the requirements of filling sachets ranging from a few tens of grams to 1.5 kg with measurement inaccuracy in the order of a gram. The measurement requirements are not very exacting, it was more the "extras" which swayed the decision in favor of the PW20i. "From the start, we wanted to have an RS232 interface so that we could connect the cell to our circuit board. Secondly, we needed a small product which would fit in well with our compact machines. Finally, we needed a product which was correctly protected against overloading", explains Thierry Cerisay. The PW20i fulfills all these conditions, it is also easy to fit, with two screws to fix it to the machine structure and two screws to fix the plate. The protection against overloading is a requirement given the bagging plate can be exposed to shocks, for example as a result of operator errors. This protection is built into the PW20i so it was possible to fit the bagging plate directly on top of the cell without having to provide additional mechanical protection. The PW20i does not require the measurement to be processed electronically. Because of its high resonance frequency, no electronic filters or reduction measures need to be applied. The PW20i's IP65 degree of protection is also a bonus, as it allows direct fitting without a protection board (in the knowledge that the products handled by the machine do not need to be washed with high-pressure water jets). Last but not least, the PW20i is a metrology product with specifications in accordance with the OIML standards. Everything is specified, especially non-centering errors where the sachet is not centered on the plate. The calibration of the machines simply requires the use of weight standards, with any corrections integrated directly into the sensor electronics. At the end of the day, there are a number of details about the PW20i which LGC Automation uses to produce simple, operational, easy to use machines at very competitive prices. Despite this, the company still faces Asian competition in its market niche. Thanks to its partnership with HBK, it has some convincing arguments to put to its future clients: "When we see the load cells fitted on some machines, we cannot help but have serious misgivings about their longevity. By comparison, the cells installed on our machines inspire confidence in every way, especially as they are provided by a leading manufacturer with extensive experience in weighing with operations all over the world", concluded Thierry Cerisay.
