One Sensor, Multiple Targets

A single linear sensor monitors multiple positions along its axis. • A single linear sensor monitors 20 positions. • Time to read 20 positions matches that of a single position. • Strokes over 5,000 mm, accuracy of ±20 μm, and resolutions of 1 μm. Magnetostrictive Sensors For Bottle Filling It is often advantageous to have a single sensor monitor more than one feedback parameter. This is now possible in the case of a linear-position sensor that can track as many as 20 moving positions along its axis. The sensor uses magnetostriction as a feedback mechanism. Sensor electronics send out an interrogation signal. The magnetic field of this signal interacts with position magnets located along the sensor axis to generate sonic waves that travel along a wave guide. The device captures the return signals over a time period corresponding to the entire length of the sensing element. It turns out this return time corresponds to the worstcase situation for a single magnet sensor. Thus it takes no more time to sense multiple magnets on a magnetostrictive sensor than to sense a single position. And a multipleposition sensor uses the same basic magnetostrictive sensing technology as a single-sensor device, so the two cost about the same. For example, sensors can sense up to 20 magnet positions simultaneously within limitations using a single sensor. One limitation of a multiple-position sensor concerns the spacing between any two magnets. If magnets are close together, their return signals literally overlap and distort from constructive wave interference. Therefore, multiposition magnetostrictive sensor applications need at least a 75-mm space between magnets. This also means any motion that brings a magnet too close to its neighbor causes a loss of signal validity. Fortunately, most applications have enough room to properly space the magnets. Or it might be possible to orient