I am currently utilizing a PowerFlex 525 drive, managed through the terminal block's digital inputs (DigIns). Specifically, I have configured DigIn 6 to control an alternate preset frequency, designated as A412. This setup also allows for the use of acceleration and deceleration 2 settings. The motor operates at a frequency of 30 Hz when the DigIn 6 input is open, and it switches to 60 Hz when the input is closed. The relevant parameter settings are as follows: P041 is set to 12 seconds, P042 to 0.2 seconds, A442 to 8 seconds, A443 to 0.2 seconds, A410 to 30 Hz, and A412 to 60 Hz. In the ladder logic program, once the machine reaches a specific condition, it activates the PLC output, which then controls the DigIn 6 on the drive. When the system operates at the 60 Hz frequency and I release the pushbutton on the HMI, the machine stops immediately as expected. However, my concern arises during operation at 30 Hz—sometimes the machine behaves as it does in the 60 Hz scenario, but occasionally the brake engages, causing the motor to sound as if it is attempting to overcome the brake. What confounds me is the intermittent nature of this issue; it is challenging to replicate consistently. The VFD is equipped with a dynamic brake resistor, and parameter A437 is set to 1. Additionally, I have configured A550 to 0 to ensure rapid motor stopping. While monitoring the ladder logic via my laptop, I can see the Output Energize (OTE) instruction turn off, and the indicator light on the PLC, which corresponds to the forward or reverse command for the VFD, also goes off. Nevertheless, when this issue occurs, the VFD display continues to show the RUN command as active. I initially suspected that electrical noise might be keeping the input to the VFD activated longer than necessary, so I distanced the control wiring from high voltage by removing it from the Panduit. However, this did not resolve the issue. I am feeling perplexed and welcome any questions, comments, or insights regarding this situation.
Is this a recent issue affecting equipment that has been functioning properly, or is the machinery relatively new? - Bubba.
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To begin with, monitor the parameter that shows the terminal block status to determine if the drive is indeed losing the run input signal.
JZerb mentioned: I am currently operating a PowerFlex 525 variable frequency drive (VFD) using the terminal block’s digital inputs (DigIn). Specifically, I have configured DigIn 6 for my alternative preset frequency, A412, which permits the use of acceleration/deceleration setting 2 with it. The motor operates at a frequency of 30Hz when the DigIn 6 input is open and ramps up to 60Hz when the input is closed. Here are the parameters I’ve set: - P041: 12 seconds - P042: 0.2 seconds - A442: 8 seconds - A443: 0.2 seconds - A410: 30Hz - A412: 60Hz Once the system reaches a specific condition in the ladder logic, the PLC output activates, controlling DigIn 6 on the drive. When the motor operates at 60Hz and I release the pushbutton on the HMI, the machine stops as expected. However, my concern arises when the machine runs at 30Hz—it occasionally behaves like it’s in the 60Hz range. At times, the brake engages, and it sounds as though the motor is struggling against the brake. What confuses me is the intermittent nature of this issue; I’m unable to replicate it consistently. A dynamic brake resistor is installed on the VFD, and I’ve set A437 to 1. Additionally, A550 is configured to 0 to achieve rapid motor stops. I can observe the ladder output (OTE) turn off on my laptop, and the light on the PLC display corresponding to the forward or reverse command shuts off as well. Nevertheless, during these problematic instances, the VFD display still indicates that the RUN command is active. I initially suspected that electrical noise might be keeping the VFD input activated longer than necessary, so I relocated the control wiring away from any high-voltage areas, but this had no effect. I’m puzzled and welcome any questions, comments, or suggestions on this matter. Regarding the persistent RUN command shown on the VFD, I’d like to inquire about the type of output you’re utilizing. Solid State PLC outputs can sometimes "leak." The inputs on the VFD require a minimum on-current, but maintaining the command requires less current. If the leakage current is near this minimum threshold, it can lead to the symptoms I'm experiencing. Using a suitably sized resistor—around 1W—as a pull-down for the VFD input has proven successful for me in connecting PLC outputs to VFDs and linking PLCs in traditional hard-wired systems. For a 24VDC setup, a 1K pull-down resistor would draw 24mA and dissipate just over half a watt when the output is enabled. Although this may consume extra power, it could effectively resolve the issue.
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