Absolute encoder read by a siemens plc.

Hello Marko Bursic

I didn't know you didn't need a library, so I downloaded it anyways. I have a question. Do you know how I can convert the decimal output to a certain position of my absolute encoder (EAW0J-B24-AE0128)? You see, according to the datasheet the decimal output and the corresponding positions are random, for example, position 0 = decimal output 127 or position 9 = 72. I want to make it linear, for example position 0 = decimal 0 and position 5 = decimal output 5.

I tried to understand, but I'm missing something.

So please, explain it to me clearly what You want to do ?

Now, I am understanding it in this way: You want to change codes assigned to your encoder. So If You set your encoder in position 0 it will give 0(p1-p8=0), it you set it for 2 it will give 2(p1,p2,p4,p5,p6,p7,p8=0, p3=1) etc. ? Am I right ?

If so, it's impossible. This device has assigned code to position and this is not changeable.

Also read some information about Gray Code - it's impossible that binary(converted to decimal) interpretation of values in Gray Code occur in order 1,2,3...

Best regards

Hello Rafal

I know, it's a very specific and complex situation. I'll try to explain it again. So imagine the encoder giving an absolute value in binary. For example: according to the data sheet position 0 = 0111111 which is 127 as a decimal output in binary and right after comes position 1 = 00111111 which is 63. The watch table in the Siemens software shows the exact same thing. When I turn the absolute encoder the value changes from 127 to 63 and so on to another random decimal value. So my question was: is there a way to make the Siemens PLC read these decimal values as a 1 and a 2 in stead of 127 and 63?

Ok, now I understand.

And the answer is yes, of course. 

You have to make decoding function.

Example:

Function will have one input - your Value from encoder. Also function will have one output, which is yours number.

Inside this function you have to make translation from input to output values. And then, in your program, You will use the output value from function.

The simplest way is to make 127 rung with comparasion of input values decoding table from manual and push required value to output depending on input.

It's not the prettiest solution, but it will work. But I am sure, that if you think some time, you will find more pretty solution.

I hope this will help You,

Best regards

OK, I thought the encoder is encoded with a gray code as stated from datasheet, but maybe it is a different kind of it. So, what you gonna need is a look up table. The datasheet states : ACETAB: 256 byte code conversion table (ROM).

So the best way to decode is to use a existing proven method, you have just to find it out.

github source

The above uses an array of 256 of numbers. I would use a DB or FB and declare a variable, like Decoder : ARRAY [0..255] of USINT

Then you fill the numbers one by one. But you can also Generate a  source from  blocks  and then paste directly, then find/replace, finally you compile from source and create the DB with all that values. 

See the below source code generated from existing FB, I have added the array ddd and then generated:

All you have to do is copy the array from source on github and then FIND 0x and REPLACE with 16#  then paste in the created source of DB/FB. Then you compile back.

Hello

Thank you for your reply Marko.

Is this possible with ladder? Because I'm still a learning student so SCL is a bit too complex for me.

Hello Rafal

You said a function block, but which one do I have to use? Also how can I translate every decimal value to my number of choice (all 128 of them)?

Can you give me an instruction please?

Regards