SSI Encoder

[benaiahhenry]

Hey Guys,

I am trying to use an SSI encoder for the first time and having problems getting any data from it.

I am using a 1738-SSIM23 Armorblock IO card and a micro-epsilon WDS-1000-P60-SR-SSI drawstring encoder. uEpsilon says that encoder is actually a Baumer GM400.010A102 (spec sheet attached)

The SSIM23 card seems to be working fine. It has no errors and the "Run" light is on. However, I can't get any data from the encoder. The input values never change from what I have in the screenshot. I've tried using 12, 13, and 25 bit word lengths, as well as all the different clock speed options.

For wiring I the Power/Comm, Data +/-, and Clock +/- wired to the appropriate pins on the SSIM23 card.

I notice in the IO structure there is a "control" output word, but I can't find anything about that in the Rockwell SSI manual for pointIO (http://literature.rockwellautomation.com/idc/groups/literature/documents/um/1734-um007_-en-p.pdf)

If anyone has any ideas as to what I'm doing wrong I'd love to hear them! As I said, this is my first time using SSI so I'm guessing there is something simple I'm missing.

Thanks!

-Benaiah

 

[cardosocea]

Off the top of my head, I would lower the SSI Word Filter to zero or the lowest setting you can get.
It may be nothing, but these (particularly absolute encoders) can be really really sensitive and you aren't receiving 5 exact words and the system doesn't take them into consideration. It's a long shot, but worth a try.

Also, have you put a scope on it to see pulses moving back and forth?

Looking at the SSI Word delay, I think that it may be a bit much considering your encoder. According to the manual it states to use the monoflop time in the encoder datasheet. The manual states 26 +T/... by my crude calculation that should be near 30 us not 64us. I don't think it's a big deal, but perhaps trying a smaller value there can help.

 

[benaiahhenry]

Off the top of my head, I would lower the SSI Word Filter to zero or the lowest setting you can get.
It may be nothing, but these (particularly absolute encoders) can be really really sensitive and you aren't receiving 5 exact words and the system doesn't take them into consideration. It's a long shot, but worth a try.

Also, have you put a scope on it to see pulses moving back and forth?

Looking at the SSI Word delay, I think that it may be a bit much considering your encoder. According to the manual it states to use the monoflop time in the encoder datasheet. The manual states 26 +T/... by my crude calculation that should be near 30 us not 64us. I don't think it's a big deal, but perhaps trying a smaller value there can help.

Thanks! I will give those things a try when i get into the plant later this morning. I'd though about putting a scope on it, but I'm working at a customer location up in Canada right now, and don't have access to one.

-Benaiah

 

[cardosocea]

It sucks carrying one... but they go hand in hand with encoders I'm afraid. Every problem I've had with one the oscilloscope came in extremely handy to prove what was going on.

I did, at one point, start working on a little tool to check up encoders with a small microcontroller, but have moved on from that line of work so don't have access to all sorts of encoders any more.

 

[John.S]

Benaiah,

Agree with the first check if clock pulses are there.
They must be generated by the interface card in your PLC.
On every clockpulse the encoder returns a logic one or zero.

So if there are no clock pulses, the first thing to look is your PLC side.
If there are pulses but no reply from encoder, than check encoder.

Also, the number of bits must match the encoder specs, but in all the systems i worked with, if number of bits do not match, you still get some values, but not the right ones. ( worked with Ansaldo SSI-cards and AEC SSI cards).

gr. John.

 

[benaiahhenry]

Thanks for the replies guys!

I've tried the settings changes that cardosocea suggested but had no luck. I didn't have a scope to check if I was actually getting pulses. We had a 4-20 laser displacement sensor here though that did work, and since we were running out of time for commissioning we used that instead.

Thanks again for your help!

-Benaiah

 

[Passman]

Stupid question, but the enable bit in the controller tags is set to true isn't it?