I am currently working with a Robicon 454GT series drive and have encountered some unusual issues. The drive was configured to utilize analog input 1, which operates on a 4-20mA scale representing 0-100%. The Loss of Signal (LOS) setting is programmed to deactivate the drive under specific conditions. However, I have discovered that the analog input signal is measuring 9.88mA even with the wires disconnected. To further investigate, I employed a 4-20mA signal generator. As I increased the output, the drive's response improved accordingly; 20mA correlated perfectly with full scale, and a reading of 16mA indicated 80%. This initially led me to believe the system was scaled for a 0-20mA range. Interestingly, even after disconnecting the wires, the drive still registered an input signal. I then switched the control to analog input 2, which performed slightly better than input 1 but still indicated a reading of 9.24mA. Notably, there are no connections at terminals TB18-19 (for analog input 1), yet it continues to show 9.88mA. I would like to adjust the input signal if possible, but I have a feeling that there may be a more complex issue at play. Any assistance or insights you can provide would be greatly appreciated.
It’s possible that some parameters may have been altered or corrupted, resulting in the current issue, but it could also indicate a malfunctioning A/D converter within the drive itself. I encountered a similar situation years ago with a budget-friendly drive that affected several channels. My experiences mirrored yours almost perfectly. The VFD displayed a 50% run command even with the wires disconnected, and it would increase to 100%. We occasionally needed to operate it at 30%, which led to my decision to replace the entire drive to resolve the issue. Initially, I attempted to adjust the minimum and maximum scale values as a workaround, but the problem persisted, and the readings continued to drift upward, leading us to lose trust in its accuracy. I suspect that many analog input modules with multiple channels utilize a single A/D converter through internal multiplexing. Unfortunately, I am not familiar with that specific drive model, so I cannot provide further assistance.
Thank you for your insights. It’s clear now that the drive, which is two decades old, is still operational. However, the scaling of the analog inputs is inaccurate in the lower range. For the PLC output, when the wires are disconnected, the readings are as follows: 0mA, 4mA, 8mA, 12mA, 16mA, and 20mA. When checking the VFD analog input with the wires detached, the readings were 8.28mA and 8.98mA. Using Analog Input 2, I recorded the following values: - 4mA: 38% - 8mA: 50% - 12mA: 60% - 16mA: 80% - 20mA: 103% (I suspect this discrepancy is due to the card outputting slightly more than 20mA. When I tested with my signal generator, 20mA displayed as 100% on the drive.) The drive is set up to operate within a 4-20mA input range where 4mA corresponds to 0% and 20mA to 100%. I do have a minimum speed setting established at 25%. Even after adjusting this to 0% for testing, the analog input values remained unchanged. Fortunately, the drive seldom functions at low speeds, so I can accept a reading of about 33% (roughly 21Hz). This is only slightly above my desired offline speed of 15Hz and does not impact burner performance. Previously, the company maintaining the drive had it running at 50% offline, which seemed excessive but not unexpected given their history.
Robicon previously relied on signal conditioners to transform the 4-20 mA current signal into a 0-5 VDC output for input into the analog input card. In my experience, I encountered significant challenges with calibration issues—both with the signal conditioners and the analog input itself. It would be wise to verify the calibration status of these components.
At just 20 years old, it's essential to begin planning a budget for a replacement drive, especially since it's a Robicon brand. The need for a replacement is definitely approaching quickly.
DickDV emphasized the importance of planning for a replacement drive at just 20 years old, particularly given that it's a Robicon model. The time for action is certainly upon us. With nearly two requests per week for swapping out older 454GT drives, it's clear that Siemens is stepping back from supporting the outdated Robicon NIH (Not Invented Here) drives. Instead, they're pushing users toward their German-manufactured Siemens drives, warning of lead times that can stretch between 30 to 50 weeks for replacement Robicon control boards. Thus, it's essential to begin making new plans for your equipment. Additionally, don’t fall into the trap of thinking you can easily find replacement boards on eBay. There's one major California-based user who monitors the market closely and purchases every available board as soon as it’s listed, regardless of whether they currently need them. They send these boards, whether functional or not, directly to re-manufacturing companies for repairs. The situation is quite remarkable!
It sounds like you're dealing with a tricky issue that could be influenced by a few different factors. The persistent 9.88mA reading suggests a possible grounding or interference issue, maybe a floating input or noise in the system affecting the analog input. Have you checked the wiring closely for any shorts or resistive paths? Sometimes, even a minute voltage leakage can create a false signal. Also, consider reviewing the input configuration settings in the drive to ensure they're properly assigned, as a misconfiguration there might contribute to these inconsistency issues. It might help to temporarily disconnect everything and see if the LOS is triggering under those conditions to better isolate the problem. Good luck—these situations can be a bit of a puzzle!
It sounds like you’re dealing with a pretty perplexing issue there! The persistent 9.88mA reading even with the inputs disconnected is unusual and might suggest a grounding problem or some form of noise interference that’s causing phantom current to be detected by the drive. Double-check your grounding and ensure that all connections are clean and secure. It might also be worth inspecting the analog input circuitry for any potential faults. If you haven't already, reviewing the drive's configuration settings to confirm there’s no mix-up between the 4-20mA and 0-20mA scaling can help clear up some confusion. Good luck, and keep us updated on what you find!
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