Linear position sensor takes the biscuit

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When the UK subsidiary of a multinational food and beverage equipment manufacturer sought to upgrade and simplify an automated dough thickness adjustment process across its range of biscuit baking machinery, it turned to Positek and its P103 series LIPS short-stroke linear position sensor to provide precise measurement of the gauge roller gap position.

Linear position sensor takes the biscuitThe gauge rollers form the dough into a flat sheet (of the required thickness) in a continuous process before the biscuit shapes are cut out prior to the baking process. Controlling the thickness of the dough sheet is important for consistent quality and material costs, but in this case it also needs to facilitate different products to be produced, so fast changeover times are important. The previous sensor, an older LVDT type, required a special electronics module to convert its signal to suit the machine’s PLC, and further, all components needed a good deal of electrical calibration to compensate for the non-linearity of the electrical response before changeover. Added to this, a relatively long overall length plus the large diameter for the previous LVDT sensor made the gauge roller assembly bulky.

Positek’s P103 series short stroke linear position sensor with LIPS technology is ready-calibrated to the exact travel required, so could be directly installed into the machine for each set of paired gauge rollers without the need for extensive (and costly) setup. Positek’s LIPS technology is based on inductive coils and uses a custom integrated circuit to produce an accurate analogue output signal. Its standard two-wire 4–20mA output directly interfaces with the PLC and simplifies the previous wiring arrangement. With a linear response to within +/- 0.25 per cent of the travel range and an extremely low temperature coefficient error, the sensor has improved the accuracy and long-term signal reliability. The net result is reduced machine recalibration and maintenance requirements.

With no need to incorporate adjustments in the PLC, installation and commissioning is now faster and less complicated. The sensor’s mounting flange face provides convenient mechanical interfacing and is used as the reference for factory calibration, so when installed on the machine the only adjustment required is setting an initial mechanical datum for the roller gap using a Vernier gauge. The P103’s housing diameter is just 35mm and, with the output calibrated to the measurement travel required, the short-stroke linear position sensorĀ“s nominal length remains compact with no unwieldly overhanging components for the gauge roller assembly. The new sensor has stainless steel construction together with IP65 sealing (IP67 available on request) and a wide operating temperature range of –40degC to +125degC.

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