Encoder Counting/tracking

Hi PLC-Programmers!

In my application where i use a absolut encoder to keep track of a conveyer, i use a S7-200 224XP.

Output from encoder is 10bit(1024)Gray-code.
Until now i can read encoder value(MW?), from 0 to 1024 and then start over again.
The converter from gray to binary is working ok.

The encoder outputs a signal, that tells the direction.
High:backward Low:forward

Question: How can i continue conuting from 1024 and upwards and then downwards again.
Shall i use registers or what.

Thank you
hjajoe

Your plc program must sample the encoder such that the change seen between samples does not exceed 256 counts.

If Initialising then LastEncoderValue = CurrentEncoderValue

If (CurrentEncoderValue - LastEncoderValue) < -512 then
increment RevCounter

If (CurrentEncoderValue - LastEncoderValue) > 512 then
decrement RevCounter

e.g.

hjajoe said:

Hi PLC-Programmers!

In my application where i use a absolut encoder to keep track of a conveyer, i use a S7-200 224XP.

Output from encoder is 10bit(1024)Gray-code.
Until now i can read encoder value(MW?), from 0 to 1024 and then start over again.
The converter from gray to binary is working ok.

Click to expand...

You have the hard part done.

The encoder outputs a signal, that tells the direction.
High:backward Low:forward

Question: How can i continue conuting from 1024 and upwards and then downwards again.
Shall i use registers or what.

Click to expand...

After converting to binary you need to:
1. subtract the last binary 10 bit encoder value.
2. shift the result left 6 places. The MSB will now provide the direction.
3. Shift the result right 6 places using an arithmentic shift. The sign bit should be shifted into the upper bits as the the number is shifted right.
4. add this to a software counter INT or DINT.

Encoder tracking

Hi Peter!

Is it possible for you to give me an program example in ladder.

thanks to Peter/LD AR2 for answering.

hjajoe