Sensors Cope with Harsh Environments

For position sensing in tough factory conditions, the sensor must come in its own protective enclosure to withstand the rigors of the application, as well as satisfy increasingly tougher performance specifications. The International Electrotechnical Commission (IEC) ingress protection (IP) is a frequently quoted measure of how well it is sealed. The first number in the rating, six, indicates the equipment is dust-tight and the second digit rates the amount of water ingress allowed. Common water ingress numbers for sensors include: IP65, IP66, IP67 and IP68. IP65 indicates protection against low-pressure jets from all directions for 1 min with limited ingress permitted. IP66 is similar except protection is against direct sprays. IP67 indicates the sensor is protected against the effects of immersion from 15 cm to 1m for 30 min without water ingress. The most difficult of these ratings is IP68, for protection against complete continuous submersion in water without water ingress under conditions specified by the manufacturer. All of the following sensors have an IEC IP rating and meet tough accuracy and other performance requirements.

LINEAR INDUCTIVE PROXIMITYMEASUREMENTS

Pepperl+Fuchs’ PMI14V-F112-U-V3 inductive linear measurement sensor has a 14-mm sensing range with resolution up to 0.033 mm. With 0 to 10V analog output, the units have a zero position adjustment providing the flexibility for scaling to shorter usable lengths. Any ferrous metal can provide the target for the inductive sensor. The 35-mm wide x 41-mm deep flush mountable sensors have a repeatability of ±0.05 mm and linearity of ±0.4 mm, providing high performance for short-range linear measurement in a compact package. In addition to short circuit, overload and reverse polarity protection, the linear sensors have an IP67 rating. Target applications include spindle gripper position measurements in the machine tool industry.

POTENTIOMETER REPLACEMENT

Macro Sensors’ LP 750 Series Position Sensors are ¾- (19-mm) in diameter, hermetically sealed position sensors that can replace potentiometers. Both the pre-calibrated loop-powered 4-20 input/output (Model LPIR) and the nominal 24V dc input, 0 to 10V dc output (Model LPER) are available with standard ranges of 4 to 25 inch (100 to 600 mm). In addition to a standard maximum linearity error of ±0.25 percent of full-scale output (FSO), an optional linearity error of less than or equal to ±0.1 percent FSO is available. Using linear variable differential transformer (LVDT) technology, the frictionless position sensors offer infinite cycle life and higher reliability than potentiometers. Sensors are constructed entirely of stainless steel and hermetically sealed construction allows the sensors to meet the IEC IP68 standard and survive hostile environments. The sensors target industrial position measurement applications including machine tool positioning, hydraulic cylinder positioning, valve position sensing and automatic assembly equipment.

COMPACT PROXIMITY SENSOR

Measuring 10 x 10 x 28 mm, TURCK’s uprox+ sensor with a Q10S housing targets the requirements of the mounting and handling industries. The Factor 1 sensor achieves high switching distances for all metals and offers a large degree of mounting freedom. In addition to mounting directly on metal, with an intermediate metal plate the sensor can also mount directly beside another one. With non-flush and partly flush mounted versions, the sensor achieves a switching distance of 5 mm. The fully flush mounting unit reduces the safe switching distance to 2.3 mm but eliminates the need for an additional flush version. Operating in a temperature range of -30 to 85C, the sensor has a chemically resistant and mechanically robust polypropylene housing. The sensor is offered with both a rugged oil-resistant PUR cable, as well as a pigtail version with an M8x1 connector.

POTENTIOMETER SENSOR

Rugged enough for position feedback in wet environments and outdoor applications with an IP67 rating, Celesco Transducer Products’ SR1A-125 string pot has a potentiometer cycle life of 250,000 cycles. Using a conductive plastic precision 10 kO potentiometer, the cable-extension transducer has a 125-inch stroke, 0.5 percent accuracy and essentially infinite resolution. With a maximum input voltage of 30V dc applied, the movement of the spool with its coupled potentiometer produces an output voltage directly proportional to the position of the measuring cable. Initially designed for off-road construction equipment, the unit has a polycarbonate enclosure and 0.034-inch nylon-coated stainless measuring cable that has a constant cable tension of 23 oz ±30 percent ounces.