Reading SSI Absolute Linear Encoder

[PeterGrant]

Hello there,

I’m attempting to read an SSI Absolute Linear Encoder, however being a mechanical engineering playing with electronics I have what I would assume are some basic questions.

The hardware I’m planning on using is as follows:

• cRIO 9067
• NI-9375
• Renishaw/RLS LinACE encoder - SSI http://www.rls.si/linace-absolute-linear-shaft-encoder

Here begins my level of ignorance:

1. I need to create my clock, which will be a simple on/off digital signal on the FPGA, however what I’m not sure about (and can’t find anywhere, assuming I’m googling the completely wrong things) is this a voltage (5V as this is what the encoder is powered by?) or is the clock generated in a different way? Sideline NI-9375 appears to be a 30VDC output, is that not adjustable?
2. Is the high side data stream 5V as well?

Sorry my ignorance! And thanks in advanced.

Peter

[NataliaS]

Hi Peter,

Oh boy, I do have homework for you and questions of course so that we get a bigger picture:)

Let's take a look at a couple of things, for example, why do you chose to implement in FPGA?

- What does the datsheet of the encoder say, what inputs does it require? how does it need to be connected, how does it communicate?

- The digital clock - why would you need to implement your own signal, where is it going to be used?

               - Or do you mean the NI 9375 to have a digital output of 5 V high and 0 V low alternating?

- What frequency are we talking about? 

- In NI 9375 data sheet stated is  :

• 6 V to 30 V output range (based on supplied voltage) 
• https://www.ni.com/docs/en-US/bundle/ni-9375-specs/page/specs.html
• --> Read on how to limit the output voltage based on what your requirements are for the encoder. 

Now lets look into background infromation that is going to get you running in no time: 

--> Getting started with CRIO -> especially check the "Scan Mode Session"

https://knowledge.ni.com/KnowledgeArticleDetails?id=kA03q000000x0UdCAI&l=en-US

--> How does it actually work, the scan interface?

https://www.ni.com/en/support/documentation/supplemental/08/understanding-ni-compactrio-scan-mode.ht...

--> However, if you wish to continue with the FPGA follow the below tutorials

https://learn.ni.com/learn/article/getting-started-with-fpga

Looking forward to hearing from you!

Kind Regards,

Natalia

Applications Engineer

[OA1]

These are the outputs of the encoder you've selected.  (CAN, SSI, PWM and serial RS422).

I'd recommend Ni Xnet or Serial to read your signal.

[PeterGrant]

Hi Natalia,

Thank you for the reply. 

Amazingly I've had success through a different route, via a SEA 9521, which I had discounted as deep down in a manual it mentioned it doesn't work with actuators. I switched to BiSS-C instead of SSI and got it working pretty quickly. 

In reference to your comments below, thank you for the explanations. FPGA was for speed (sometimes over 10kHz logging required). The clock was required for the input to the encoder, although the SEA now handles this for me. I hadn't picked up that the DO from NI 9375 was based on it a supply voltage you give it.

Thankfully I've been on the Embedded control course, which has definitely helped! 

Thanks again, 

Peter