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Join Date: Oct 2010
Posts: 14

# Encoder

04/17/2012 4:19 AM

which type of Input card are uses in PLC system for Absolute & Incremental Encoder connection.

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Guru

Join Date: May 2006
Location: Reading, Berkshire, UK. Going under cover.
Posts: 9171
#1

### Re: Encoder

04/17/2012 6:52 AM

Absolute: Digital Input (with as many inputs as the number of bits in the encoder output). You may find a dedicated encoder card, or you may need to convert the encoder output code (probably Gray code) to binary.

Incremental: Quadrature up/down counter for A and B (you can implement this with 2 digital inputs and some ladder logic for low speeds). You may or may not want to include the Z input - many quadrature counters in PLCs have provision for Z.

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Active Contributor

Join Date: Oct 2010
Posts: 14
#3

### Re: Encoder

04/17/2012 1:07 PM

How Digital Input card gives us the rotation angle when we uses absolute encoder?

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Join Date: May 2006
Location: Reading, Berkshire, UK. Going under cover.
Posts: 9171
#4

### Re: Encoder

04/17/2012 6:19 PM

Example:

Assume the encoder has 4 bits of resolution - the digital inputs (possibly after converting the code) will give a number between 0 and 15.

0 then represents 0°, and each other number represents (the number x (360/16))°.

So if the number was 8, for example, the shaft angle would be (8 * (360 / 16))° = 180°. OK?

Here's a table which may explain it better:

 Input 3 Input 2 Input 1 Input 0 Gray Code Binary Code Decimal Number Angle 0 0 0 0 0000 0000 0 0.0 0 0 0 1 0001 0001 1 22.5 0 0 1 1 0011 0010 2 45.0 0 0 1 0 0010 0011 3 67.5 0 1 1 0 0110 0100 4 90.0 0 1 1 1 0111 0101 5 112.5 0 1 0 1 0101 0110 6 135.0 0 1 0 0 0100 0111 7 157.5 1 1 0 0 1100 1000 8 180.0 1 1 0 1 1101 1001 9 202.5 1 1 1 1 1111 1010 10 225.0 1 1 1 0 1110 1011 11 247.5 1 0 1 0 1010 1100 12 270.0 1 0 1 1 1011 1101 13 292.5 1 0 0 1 1001 1110 14 315.0 1 0 0 0 1000 1111 15 337.5
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Join Date: Apr 2008
Location: Lexington, KY
Posts: 1447
#2

### Re: Encoder

04/17/2012 12:26 PM

It may depend on the brand or manufacturer of the PLC you want to use.

Beckhoff Automation uses an EL5151 card as a dedicated encoder interface. Allen Bradley uses a couple of types depending on the model of controller you want to use.

High speed counters will frequently be used with a separate input for reseting to zero.

Happy Hunting!

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