Hello everyone, I'm reaching out for assistance as I'm using an SSI encoder for the first time and encountering challenges when trying to retrieve data. My setup includes a 1738-SSIM23 ArmorBlock I/O card along with a Micro-Epsilon WDS-1000-P60-SR-SSI drawstring encoder. Micro-Epsilon has indicated that this encoder is essentially a Baumer GM400.010A102 (please find the spec sheet attached for reference). The SSIM23 card appears to be functioning correctly—it's error-free and the "Run" indicator is illuminated. However, I'm unable to receive any data from the encoder; the input values remain static, as shown in the attached screenshot. I have tested various configurations, including 12, 13, and 25-bit word lengths, along with multiple clock speed settings. Regarding the wiring, I've ensured that the Power/Comm, Data +/-, and Clock +/- are connected properly to the designated pins on the SSIM23 card. I've also noticed an output word labeled "control" within the I/O structure, but I've been unable to find any details about it in the Rockwell SSI manual for Point I/O (available here: http://literature.rockwellautomation.com/idc/groups/literature/documents/um/1734-um007_-en-p.pdf). If anyone has suggestions or insights on what might be going wrong, I would greatly appreciate your feedback! As this is my initial experience with SSI encoding, I'm sure I'm overlooking something straightforward. Thank you in advance for your help! Best, Benaiah
To optimize the performance of your SSI (Synchronous Serial Interface) system, I suggest adjusting the SSI Word Filter to its minimum setting or zero. While it may seem insignificant, particularly with sensitive absolute encoders, any discrepancies in word counts—such as not receiving exactly five words—could impact system performance. It’s unlikely to solve the issue, but experimenting with this adjustment could be beneficial. Additionally, have you employed an oscilloscope to monitor the pulse signals? Evaluating the SSI Word delay might reveal that it's excessive for your specific encoder setup. The encoder manual recommends consulting the monoflop timing parameters listed in the datasheet. The specification indicates a delay of 26 +T/... and, based on my rough calculations, it should be approximately 30 microseconds instead of 64 microseconds. While this may not seem critical, reducing this value could improve system functionality.
User cardosocea suggested: "Based on my initial thoughts, I recommend adjusting the SSI Word Filter to the lowest possible setting. While it might seem insignificant, absolute encoders can be extremely sensitive. If the system isn’t recognizing five exact words, it might be missing crucial data. Although it's a long shot, it’s definitely worth experimenting with this adjustment. Additionally, have you considered using an oscilloscope to observe the pulse signal? Regarding the SSI Word delay, I believe it could be excessive for your specific encoder. The manual advises utilizing the monoflop time indicated in the encoder's datasheet. It mentions a value of 26 +T/... which, based on my rough calculations, should be approximately 30 microseconds rather than 64 microseconds. While this may not seem critical, testing with a smaller value could yield positive results. Thanks for the advice! I’ll try these suggestions when I return to the plant later this morning. I had considered using an oscilloscope, but I’m currently working at a customer site in Canada, and unfortunately don’t have access to one." – Benaiah
Dealing with encoders can be quite a hassle, but unfortunately, they are often intertwined with oscilloscope usage. In every instance I've faced a challenge with an encoder, having an oscilloscope on hand was invaluable in diagnosing the issue. At one stage, I began developing a compact tool utilizing a microcontroller designed for checking encoders; however, I have since shifted my focus and no longer have access to a variety of encoder types.
Benaiah, Initially, it's crucial to verify the presence of clock pulses, as they should be generated by the interface card within your PLC. Each clock pulse prompts the encoder to return a logic signal of either one or zero. If clock pulses are absent, begin troubleshooting on the PLC side. If clock pulses are present but there’s no response from the encoder, the encoder itself may need to be examined. Additionally, it's important to ensure that the bit count aligns with the encoder specifications. However, based on my experience with Ansaldo SSI cards and AEC SSI cards, even if the bit count doesn’t match, you might still receive some readings, albeit inaccurate ones. Best regards, John
Thank you all for your responses! I implemented the settings modifications recommended by cardosocea but unfortunately did not achieve the desired results. Lacking a scope to verify if I was receiving pulses, I turned to a 4-20 laser displacement sensor that was available. Given our tight timelines for commissioning, we opted to utilize that sensor instead. I appreciate your assistance once again! - Benaiah
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