With the use of magnetic position generators, a mechanical connection to the sensor such as a potentiometer is needless. Corresponding systems deliver exact measurements and do not wear because of their closed housings. Despite their high price, distance and angular sensors with magnetic position generators are used in numerous fields of applications. 

However, magnetic measuring systems are unsuitable where metallic splinters or electromagnetic fields are present. Furthermore, magnetostrictive linear displacement sensors have a large blind zone of up to 80 mm at each side -- with a measurement range of 50 mm at each side the user would have to trade off an installation length of up to 210 mm. 

Turck has developed new distance and angular measurement sensors to put all these disadvantages in the past. Unlike magnetostrictive or conventional inductive position sensors that use magnets, the new sensor detects an object’s position via a resonant positioning device. 

The functional principle involves a transmitter coil integrated into the IP67-rated housing that generates a high-frequency alternating magnetic field (190 kHz) which activates the resonator integrated in the positioning device. Each time the transmitting coil stops transmitting, the resonator induces voltage into two receiving coils integrated in the sensor. The voltage intensity depends on where the positioning device overlaps the receiving coils. An integrated 16-bit processor provides a corresponding proportional output signal in different formats: 0 to 10 V, 4 to 20 mA, IO-Link or SSI. 

Unlike magnetostrictive sensors, this resonant circuit principle is completely immune to external electromagnetic fields, like those caused by large motors or welding cells, and since there are no magnets involved, splinters do not accumulate on the positioning device. Unlike potentiometric detection solutions, not even dirt nor dampness affect the sensor – thanks to a fully sealed IP67-rated housing. 

Turck uses the resonant circuit measuring principle for three sensor families. The miniature linear displacement sensor was developed especially for a very short measuring range between 50 and 200 mm. The compact miniature sensor completes the portfolio consisting of the inductive RI-series of angle sensors and the inductive displacement sensors of the LI-Q25-series that cover a measuring range of 100 to 1000 mm. 

The new (2011) IP67-rated LI-Q17, with potential for wind turbine and solar panel positioning applications, consists of four different models with measuring ranges 50, 100, 150 and 200 mm. With the 12-Bit-DA-converter, the sensors reach 0.012 to 0.05 mm. The first models have an analog output (0 to 10 V, 4 to 20 mA, 0.5 to 4.5 V). An SSI model is in development. 

Despite their compact design, Turck's new sensor family has extremely short blind zones of 10 mm at the connecting end and 22 mm at the head end. For the connection, a pigtail with a 30 cm cable and an M12 connecter or an open connection line of 2 m is needed. 

The LI-Q17 is the next step in the resonator-technology that Turck presented for the first time with the linear displacement sensor series, LI-Q25. The LI-Q25 sensors have a resolution of 1 um (repeat accuracy 10 um) and are especially suitable for applications like mills, injection molding plants or metal processing machines that have problems with the technical restrictions of the established measuring systems. 

Along with the linear displacement sensors, the resonator portfolio contains a series of angular sensors. The RI-sensors have a measurement range of 360 degrees at an accuracy of 0.15% of the full scale. The separated assembly of the sensor unit and the positioning device, as well as a compensation of +/-4 mm, provides an easy installation and a safe operation of the sensors. The RI-sensors can be easily attached with two shoulder bolts to solid or hollow shafts. With the help of an integrated adapter with a diameter of 6 mm and 8 mm, a standardized hollow shaft sensor can be altered into a solid shaft sensor. 

Andre Brauers is the product manager linear displacement sensors and encoders at Turck Germany in Mulheim (www.turck.com). This article is excerpted from more@TURCK magazine, issue 1_2011 (www.turckbanner.co.uk/products_986.htm).
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