Read position from a SSi encoder using PCMCIA+SCXI

[koniker]

Hi,

I need to make some position measurements over a machine. So, I need to read the position information from a rotary encoder with SSI interface and gray code (ROQ-424 from Heidenhain). Up to now, I have used, for another measurements, a NI platform in which I connect my laptop to a SCXI chasis, and different SCXI boards using a PCMCiA. Well, my system is really compoused by a DAQCArd6062E (PCMCIA), SCXI-1001 (chasis) and SCXI-1100 (analog input) and SCXI-1300, as terminal Block. But I would like to know how I should update my system in order to read the information from the encoder. I need to use a laptop, because I need a portable system. Otherwise, if the problem is the encoder type, which type could be useful?

Thanks in advance for your collaboration.

Regards,

Koniker

[JaimeC]

Hi Koniker,

NI officially don't support absolute encoders. The only type supported is quadrature encoders. You will find lots of information in our website about how to work with quadrature encoders. Also example code about how to make those measuraments is available.

Just using one of the counters of your DAQ card you would be able to read those kind of encoders and get the measurament.

As you are using a DAQ-SCXI you are using a multiplexed mode to communicate the SCXI chassis with the DAQ card. That means you are only using 4 digital lines and the analog input 0 of the DAQ card for the communication. You should need/buy the SCXI-1180, that is a simple module for the SCXI chassis which allows you to acces to the unused ports/terminals of the DAQ card and don't cost so much. That way you should be able to connect the outputs of your encoder to the counter inputs of the DAQ card.

Another more complicated/expensive solutions if you don't have other choice than using this encoder could be the next ones:

1. make some "extra" circuitery to convert your gray encoder output into a quadrature encoder and then procedure as explained before.

2. Use a fast clocked digital card for reading the data from the encoder and then process it to get the measurements.

I recomend you to work with a quadrature encoder, it would be cheaper and easier.

Hope you can go on with that information,

Thanks for using our products,

Regards,

Jaime Cabrera

NI Applications Engineering