Engineers know harsh environments can wreak havoc with feedback devices such as encoders, even causing them to fail prematurely, turning them into regular maintenance items. But what exactly does “harsh environment” mean? “There's not one type of harsh environment. There are actually many,” says Dennis Horwitz, vice president at feedback device maker Micronor. He goes on to list lightning, sand, dirt, corrosive substances, washdown needs, electrical noise, explosives, radiation, temperature, humidity, shock, pressure and altitude as just a few of the environmental conditions engineers may need to consider when picking an encoder that's right for its environment. And just as there are many types of harsh conditions to consider, there are also many different ways to ruggedized encoders, ranging from the use of high-tech solutions like fiber-optics to relatively simple mechanical changes to traditional encoder designs. Here's a look a two new encoders that take the latter route.
To fight against the possibility of contamination in dirty or washdown environments, SICK STEGMANN Inc. made its VFS 60 motor feedback device available in a blind hollow-shaft configuration. According to company President Scott Hewitt, the blind hollow shaft designs have just one point of potential access, which reduces the chance that dirt, dust or washdown water will worm their way into the encoder. “Hollow shaft clamping provides substantial increases in overall encoder reliability and immunity to electrical interference, especially when mounting to asynchronous motors, due to electrical isolation between the motor shaft and encoder,” Hewitt says. He adds that hollow shaft clamping also provides easy mounting while minimizing the run-out problems associated with collets. VFS 60 blind hollow shaft encoders, which have nickel code disc, are designed to operate in temperatures as high as 100C. They are IP65-rated and deliver from 1 to 10,000 ppr in an industry-standard 60-mm housing. They feature a radial/axial cable outlet to reduce installation depth and allow one encoder type to be used for various applications. These VFS 60 models are available with TTL and HTL interfaces.
Analog Encoders for Washdown Applications
Micronor came out with a pair of high-resolution analog output encoders for applications with tough shock, vibration, temperature and moisture conditions. Both encoders, a hollow-shaft model called ENA361M and a solid-shaft model called ESA361M, provide 12-bit resolution and offer a choice of analog outputs. According to Dennis Horwitz, a Micronor vice president, the units can handle shock up 500g and vibration to 30g. They're designed to cover a temperature range from -40 to 85C. And both units are sealed to meet IP67 requirements — with an IP69K option available for high-pressure, high-temperature washdown applications. These single-turn absolute encoders are offered with choice of 4-20mA or 0-10V output and measuring range options of 45, 90, 180 or 360 degrees. These units also operate over a wide input power range of 18-30V dc. The 4-20 mA option includes a red LED fault indicator for sensor break detection and monitoring of power supply. Overall diameter for the encoders is 36 mm. The ENA361's blind hollow shaft ranges from 6 to 10 mm and has either stator-coupling or torque-stop mounting options. The ESA361's solid shafts range from 6 to 8 mm and offer standard syncho-flange mounting.
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