Case Study P103
New sensor makes life simpler for bakery machinery makers - and users
An additional option to the Series 2000 gauge roll offered by Sasib Food & Beverage is a motorised roller gap adjustment which greatly reduces the amount of fiddly adjustment needed to ensure a consistent dough sheet thickness and which also permits the gap to be automatically adjusted for different dough products.
Sasib Food and Beverage manufactures a wide range of baking machines for producing food products from flat sheet dough such as crisps and biscuits. During the continuous process, gauge rollers form the dough into a flat sheet of the correct thickness before the biscuit shapes are formed, cut out and baked. The control of the thickness of the dough sheet is important for the quality and standards of the finished product.
At the heart of this new refinement is the Positek P103 Linear Inductive Position Sensor mounted at each set of the paired gauge rolls. The sensor measures the gap between the rolls and relays the information to the PLC. The adoption of the Positek LIPS® sensor in preference to the older LVDT sensors has saved the manufacturer both time and money according to Geoff Speak, Electrical Manager for Sasib's Food & Beverage Machinery Division, because the P103 comes ready-calibrated. The sensor is now operating on a number of sites throughout the world.
The sensor has a flange mounting which provides a well-defined reference face for mounting with two easily accessible mounting holes. The sensor is supplied by Positek calibrated to within ± 0.25% of the overall range both for the slope and the offset of the output. The flange is used as the reference when it is calibrated. When installing the sensor it requires only mechanical adjustment by a Vernier screw incorporated into the roller mechanism to take account of mechanical tolerances in the mechanism; installation and commissioning is now a much speedier and less complicated operation than it was in the days of the LVDT sensors which needed careful and long winded electrical calibration.
The internally-integrated Positek sensors permit further simplification of the new Sasib gauge roll because the output is a loop powered two-wire 4-20mA format. The older LVDT sensors needed a special electronics module separated from the sensor to convert the output to mA and to avoid the voltage drop which would otherwise occur over the often considerable distances between the sensor and the PLC. The old electronic module needed to be wired up with the sensor with multiple connections. The Positek sensor has just 2 connections to make resulting in quicker installation.
A further advantage of the LIPS® sensor derives from its fully linear response over the entire mechanical range. The sensor provides a linear response to within ± 0.5% of the travel. This means that not only is there no longer the need to incorporate adjustments in the PLC to correct the non-linearity of the LVDT response but also that the same sensor units can be used for a much wider range of dough sheet thicknesses - and hence product lines. As well as the good linearity, the Positek sensor has a very short body length compared to the travel which helps to save space in the application.
The P103 sensor is a standard sensor with a small special modification requested by Sasib. It incorporates technology developed by Positek and used in its other displacement sensor products. This PIPS® technology is based on inductive coils and uses a unique custom integrated circuit to produce an accurate analogue output signal. Several versions of the P103 sensor are supplied for different gauge roll travels from 10mm up to 50mm.