TECHNOLOgy REViEW > continued Understanding resolution in optical and magnetic encoders


designed for less demanding applications, with an operating temperature range from -40o to +70oC, a maximum speed of 120 rpm, a life of 2 million revolutions (at 30 rpm) and a maximum positional resolution of just 64 pulses/revolution. These optical encoders are primarily targeted at HMI applications like panel-mount controls in test & measurement equipment and professional & consumer audio products. Vishay Intertechnology Inc. is another


leading manufacturer of magnetic rotary encoders. All provide either a linear analogue or PWM output from a single signal wire, like the Bourns® AMS22S. The Vishay 981HE is targeted at harsh environments and intended for throttle position sensing so has the widest operating temperature range (-40o to +125oC) and enhanced performance in terms of vibration, shock and immunity to electromagnetic interference. It is rated for 120 rpm and a life of >10 million cycles (for the D-shaft model). The Vishay 34THE is a ten-turn servo encoder, which means it can measure angles up to 3600o with 12-bit resolution. It is targeted at “off-road” steering and actuator applications. The servo model has ball bearings to provide long life (50 million cycles). Next is Vishay’s 50SHE single-turn, 120


rpm, servo-mount model. This is their smallest unit, with a body measuring just 12.7mm in diameter and 19.5mm in length. Like the 981HE it is targeted at harsh environments but ball bearings provide a longer 50 million- cycle life. Finally, there is the 351HE 120 rpm, single-turn, bush-mount encoder. This has a more conventional 22mm diameter body and generally a lower specification compared to the 50SHE. Where Vishay favours magnetic encoders;


Grayhill Inc., offers a very wide range of optical encoders. These, like the Bourns’ optical encoders, are 2-bit, incremental, quadrature code output devices. In the MMI area, Avnet Abacus carries for example the 61K and 63K models, which represent the low- and high- end performance options in terms of speed and life cycles. Both feature 4-pin connections and resolution up to 256 positions / revolution but the 61K is a 300 rpm part, specified for 10 million cycles, while the 63K uses ball bearings to achieve 5,000 rpm and 300 million cycles. While this article mainly covers MMI


products, we should mention that Grayhill offers one of the broadest spectrums of optical HMI solutions, including highly integrated components like the NavCoder and the Multiturn Ring Encoder.


conclusion Rotary encoders are used to measure angular position or speed for control and feedback purposes across a wide range of applications, spanning industrial, automotive, medical and consumer. Modern designs favour non-contact sensing methods, either magnetic or optical, for improved reliability, performance and life expectancy. In practice we find the optical types cover the requirement for incremental, quadrature output signals to simply measure position change or rotational speed, while it is the magnetic types that typically provide absolute position information. Although not a fundamental limitation in the design of optical encoders, none of the models considered offer more than 256-position (8-bit) resolution whereas the magnetic types feature 10- and 12-bit resolution models. Beyond this, the differentiation lies in


the maximum speed and life expectancy of the encoder (primarily determined by bearing type), other environment factors (e.g. temperature range) and physical attributes such as their dimensions, electrical terminals and ruggedness (shock, vibration, etc.). Last but not least will be the cost consideration – clearly high performance, long life and ruggedness all come at a price.


Panasonic electric double layer capacitors (gold capacitors)


Panasonic’s gold capacitors were developed by their Central Research Laboratory in 1972 and introduced to the commercial market in 1978. They perform like a battery and are therefore ideally suited for applications requiring a secondary power source such as backup energy for microprocessors e.g. a real time clock.


Replacing a battery with a Gold Capacitor has the following advantages: » Quick charge and discharge available


» No charge and discharge cycle limitation in terms of number of times


» Green product (RoHS compliant) » No recycle restriction » No charging protection circuit needed and easy circuit design


» Maintenance free and very long life www.avnet-abacus.eu 14 focus magazine - issue 16


high reliabilTy rf and rg series The RF and RG series have the highest reliability of all Panasonic’s gold capacitors. They are defined with a lifetime of 2000h @ 85°


the current F-Series). They are therefore the best solutions for all applications requiring high reliability and long life such as metering, base stations, blade server’s and more.


feaTures Rated voltage Capacitance


3.6V / 5.5V 0.1F to 1F


Temperature range -25° Endurance


C to +85°


for more information visit avnet-abacus.eu/panasonic


C 2000h @ +85° C C (double


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