Need absolute rotary position encoder

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I have a design which requires absolute position sensing in about 330
degrees of rotation; quite similar to a potentiometer but needs to be rugged
(optical?) and low cost.  This will be a rather hostile environment think
automotive) so I'm pretty sure a standard potentiometer wouldn't last long.
The device should be sealed to withstand the equivalent of a marine

The output would be preferably digital, but analog could be made to work as
well.  Repeatability is the primary goal over accuracy.

An ideal device would be one which reported shaft position in degrees or
some other metric.

Does anyone have any suggestions?

Re: Need absolute rotary position encoder

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How fast is this rotation? Max speed of rotation affects what will work.

How often do you need to read results?

Are there any positions (like end stops) that must be read precisely and
repeatabile to greater accuracy than any other positions?

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How many readings Min and Max are required and can be processed?

To what resolution and accuracy? Do you want to read every 5 degrees or
down to 0.5 degrees?

There are various shaft and rotation encoders around that either produce
quadrature encoding or digital o/p (usuaully 256 values), but rarely have
end stop information, the most crucial part everyone forgets on limited
travel equipment driven by motors.

Other various forms of position sensing (linear, displacement or rotational)
are often done as potentiometers made of conductive plastics for long life
and easy sealability.

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The first company I would look at for this sort of thing even sealed for
marine (including submersible) components would be Penny and Giles, now
part of Curtis Wright group.


I have used them for faders, joysticks on studio video and remote control
equipment and for other industrial applications over the years. They are
damn good parts to use at the user interface and position sensing but most
require A/D, which means less wires from point of sensing to capture point.
This way you determine how accurate you want results.

Digital O/P methods mean you have to keep up with the data stream of variable
data rate and ensure you are reading a steady value (even in Grey coding).
Some require to clock every value in which may be too much overhead
depending on your system and interface. The generation of a clock may be
a challenge in itself as some produce 8 bit outputs from the sensor and you
have to work out changes and clocking methods, which at higher rotation
speeds can be tricky.

Paul Carpenter          |
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Re: Need absolute rotary position encoder
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Not exactly. With Hiperface, quadrature [1] gives 1 bit (IIRC) more
precision than the serial interface. Additional resolution is achieved by
A/Ding the sin/cos signals and doing a bit of trig. It's important to sample
both sin and cos at the same instant.

[1] Achieved by feeding sin/cos into comparators, giving 4 states per
sin/cos cycle.


Re: Need absolute rotary position encoder

Gary Pace wrote in message ...
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first time I've heard Heidenhein being recommended as low cost . Excellent
products but orders of magnitude more expensive than the OP's target price.

best regards,
matt tudor

Re: Need absolute rotary position encoder
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Sounds like a job for a resolver. If you aren't too worried about speed,
you can construct a simple phase tracker using a CPLD, otherwise Analog
have low(ish) cost RDCs available (often on long leadtimes though.

Paul Burke

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