Omron Encoder

PERSPOLIS · Mar 22, 2008

HI EVERYONE

What does resolution 256(8 bit) of an absolute encoder mean

Thanks a lot

picasso · Mar 22, 2008

hello
in absolute encoder 8 bit - 256 states per revolution
0 = 0 degree
255 = 359 degree
resolution 1,40625 degrees
regards

PERSPOLIS · Mar 22, 2008

PICASO Thank you for the reply can you please explain what do you mean by RESOLUTION 1,40625 DEGREES.

bernie_carlton · Mar 23, 2008

He was noting that 1/256 of 360 degrees was 1.40625 degrees (the comma being a common alternate to the decimal point). Thus the degree resolution of one increment of this encoder.

PERSPOLIS · Mar 23, 2008

Thanks again for the replies.
Please refer to attachment and answer these question:

1- Is it true that in one revolution (o to 360 degrees ) bits 2 to the power of 0 to 7 are generated ?

2- what the address indicate at the bottom of the page?

Thanks

bernie_carlton · Mar 23, 2008

From the timing diagram it appear that this encoder presents the data in Gray Code. If you aren't sure what that is please check here

Also check your PLC for any Gray Code conversion instructions.

Another note - the ouptu shows as NPN. Ensure you have the correct polarity on your input module.

I know you haven't actually said anything about a PLC but since this is a PLC site...

picasso · Mar 23, 2008

yes Output is in 8 bit Gray code.
Below image with difference in absolute encoder outputs.

next :
at the bottom of your document is decimal value of encoder position

Converting from Gray to binary is simply :
Sample for 4 bits
Gray Bit0 - M0.0 ( or input %I0.0 )
Gray Bit1 - M0.1 ( or input %I0.1 )
Gray Bit2 - M0.2 ( or input %I0.2 )
Gray Bit3 - M0.3 ( or input %I0.3 )
binary BIT0 - M1.0
binary BIT1 - M1.1
binary BIT2 - M1.2
binary BIT3 - M1.3
Program in IL ( Instruction List )
LD M0.3
ST M1.3

LD M1.3
XOR M0.2
ST M1.2

LD M1.2
XOR M0.1
ST M1.1

LD M1.1
XOR M0.0
ST M1.0

best regards

PERSPOLIS · Mar 23, 2008

HI
At the moment I am not concerned about programming just trying to explore this type of encoder Thanks for the input guys

_Woody_ · Mar 23, 2008

PERSPOLIS said:
Thanks again for the replies.
Please refer to attachment and answer these question:

1- Is it true that in one revolution (o to 360 degrees ) bits 2 to the power of 0 to 7 are generated ?

2- what the address indicate at the bottom of the page?

Thanks

#1 - YES (in grey code for the model you are looking at)
#2 - The address indicated is the rotational position of the encoder.

Unlike incremental encoders who can loose their position on power down, the absolute encoder will pesent its current position on being repowered even if moved.

PERSPOLIS · Mar 24, 2008

HI
Please see the attachment and I like to get clarified, my understanding from the attached drawing is that in one complete revolution of the encoder shaft in this case:
(4 bit encoder) only once those gray codes is generated and exact the same thing is repeated in next revolution and so forth.
Thanks a lot

bernie_carlton · Mar 24, 2008

You are correct.

PERSPOLIS · Mar 25, 2008

Therefore the bits are incremented in clockwise rotation and decremented in anti-clockwise rotation right? Thanks

bernie_carlton · Mar 25, 2008

Yes - just as your first PDF indicates. Just remember the code format as Grey Code.

PERSPOLIS · Mar 25, 2008

HI BERNIE

Thanking you so much for the reply, I will get back to you for more questions and I hope you do not mind it. thanks

PERSPOLIS · Apr 14, 2008

Distance Measurement

HI EVERYONE Regarding 4 bit absolute encoder after conversion from gray to binary code then each output pulses are counted and added together and result is equivalent to distance traveled for example say one meter.Thanks

Omron Encoder

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picasso

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bernie_carlton

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