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Strange software behavior for absolute encoder decoding

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Hi all

First of all.. Sorry for my bad english.. 

My software is behaving quite strange...

I have a test set-up with a driveline with a gear placed as illustrated in "System set-up".

I have two 32 bit absolute encoder rings (the encoder rings has different diameter) and 4 identical renishaw readheads.

The readheads are connected to two SEA 9521 module on a cRIO-9047.

In order to decode the raw data input from the readheads I'm using the software examples made by the SEA company.

I have attached the code in a ZIP file (I'm using the file "SEA-9521_GetPosition_Standard (FPGA)/SEA-9521_GetPosition_Standard (FPGA)_FPGA")

I did put in the right module configuration as shown in "Front panel" below.

The problem / strange behavior is the following:

- The software are working perfectly when configured for R3 and R4. R3 goes from 0 -> 360 deg, R4 goes from 0 -> 360 deg
- If I switch to R1 and R2 only one of the readsheads are working properly (though all readsheads are wirred the same way). (R1 goes from 0 -> 360 deg, R2 goes from 0 -> 192 deg ish)
- If I on the block diagram switch position of the readheads in the I/O Node R2 goes from 0 -> 360 deg and R1 goes from 0 -> 192 deg.
- When the software are working for R3 and R4.. Why isn't it working for R1 and R2???

I really need help for this one...

Thanks in advance!

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Message 1 of 4

Hey mkstech, 


You're english was perfect Smiley Happy 

I'd try reaching out to SEA gmbh Technical support as they're going to have the best knowledge of the project examples. 

Their website has a support link here or an email


Best of luck!

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Message 2 of 4

Wild guess...


Could this be a timing issue?


Does slow it down help?



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Message 3 of 4
Accepted by topic author mkstech

Hi Ben

We managed to figure out what the problem was.. 

The readhead which didn't work was actually only suited for an encoder ring with a larger diameter (100mm)... 


And the encoder ring we had was 52 mm Smiley Happy

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Message 4 of 4