I am in the IT department and need some help troubleshooting the Allen Bradley PLC in our Radyne induction heat treating machine.
The problem is - the rotating plate shaped platform has gone well below the level it usually does, I found the back plain of PLC is an old 32 bit system. How do I connect with it, solve the problem? Our go to PLC person no longer works here. Any insight or guidance would be humbly appreciated! (I'll email you pictures of the back plain, plate and control panel.)
The picture you sent us of backplane you where looking at, was not a PLC, but a supporting computer. (Understandable an IT person without PLC training would look to computer 1st ). Below is a where I mocked up the picture of control panel you sent, to show you where PLC is, and what type it is. The odds are, your problem is not in the computer you were looking down into at the backplane.
The probability of failure/change are as follows …
Sensor failure or adjustment like encoder or limit switch (physical/mechanical problem) 90% to 99% chance
Someone accessed menu on HMI screen on front of panel and changed offset 1-10% chance
Computer you have been looking at 2% (3-20% if extreme heat in panel, but symptoms do not match that type failure)
Servo Driver (device below PLC in panel) 1% (2-10% if extreme heat in panel, but symptoms do not match that type failure)
PLC (See attached picture) 1% (Within PLC, sensor input i/o most likely, symptoms do not match micro-processor itself failure)
• Get RSLogix 500 PLC training and Use PLC to troubleshoot. (See attached picture to identify which component in actual PLC that controls process.)
• Get local person trained in RSLogix 500 to troubleshoot. (I'll get Clifford of Omega Star to reach out to you, he lives in Texas. He is control automation designer we trained and runs his own consulting business.)
• Call the phone number I gave you and have machine manufacturer come out on service call.
If we trained you, what you would need for PLC troubleshooting is ...
Laptop with RSLogix 500 and RSLinx software on it. (XP would be more reliable and cheaper)
An Allen Bradley (AB) 1747-UIC or old PIC box cable to connect laptop to RJ485 port on front of AB 1747-L40 SLC 500
Discriptored backup copy of ladder logic program that is same as one in PLC. (not impossible to troubleshoot without discriptored copy of program, but extremely difficult for even the seasoned PLC expert.)
PLC Troubleshooting procedure:
Power up laptop, connect to PLC RJ485 port, go online with PLC, search ladder logic for plate home position sensor and encoder input data. Study related ladder logic, to see why it is not going to normal position. Because that process may lead you to find PLC controller is going to position set in program and set value is coming from HMI, you would need machine manual from Radyne aftermarket support packages to see how to navigate their HMI screens they designed and what setting is for position offset. If you find position is set at factory setting (not been changed) and see sensor input coming into ladder logic , you may suspect sensor adjustment or encoder failure, (servo slippage if positioning is not consistent).
Also note: If computer, Servo driver, HMI or PLC itself failed due to high heat environment, they typically have catastrophic failure and nothing would be working. Yet another indicator they are most likely not your problem. You are just using the PLC controller to troubleshoot what is the actual problem.
Common band aid fixes maintenance will do to get by problem found to be limit switch not an encoder …
Mechanically adjust offset by re-positioning home position sensor.
A more rare band-aid some do, adjust or add offset in the PLC ladder logic.
Following the above, may lead you to another problem not conceived here or so rare not mentioned here. (like old outdated program loading from eeprom on power failure.)
Henry opted for the option above for Clifford of Omega Star Controls & Technologies to go onsite to troubleshoot and investigate. The next day Clifford generated detailed report with component list, brand, model, schematics, pictures and recommended solutions to problems found. (Summary, mechanical/physical problem) For those following this thread of a real troubleshooting case study, I am sharing some of the report below, so readers may pick up a few things along the way... Initial troubleshooting of the HMI and controller revealed the software is sending and receiving inputs and outputs as expected.
Utilized the HMI to “Slow Jog” the Rotating up and the controller would fault immediately with “Abort, Error Limit” message. Attempted to perform the “Homing” function and the controller faulted immediately with the same message. In either case the faults were cleared with the HMI Controller Reset button.
Attempted to “Slow Jog” with lower limit switch actuated and the “Homing” with home switch actuated with the same results. The controller would fault immediately with “Abort, Error Limit”. However, there were no faults on the hardware.
Generated faults on the hardware by removing the connections for the encoder.
Note: Without the PLC software, unable to connect to the PLC and gain any insight and would require reverse engineering.
Further investigation into the hardware, found no blown fuses or any loose connections.
Attempted to power the servo motor disconnected from the screw-lift for the rotation plate. During the removal found the Amphenol connector for the brake release signal had been damaged. The motor side connector had been physically broken and the solder had been broken leaving the internal wiring as an open circuit. The broken solder may have been making intermittent contact for the brake would engage and disengage.
The broken connector and wire could be the initial problem for causing the brake to fail would allow the plate to continue to drop until a physical stop is reached which is beyond the predetermined lower limit switch.
As far as the controller failing to turn on the servo motor to lift the rotation plate, this could be one of two situations.
1. The encoder is not functioning properly. i.e. the controller is sending the signal for the servo motor to rotate and is not receiving the expected encoder pulses and would abort the attempt to protect the drive.
2. The brake on the servo motor is failing to release at the appropriate time causing the servo motor not to turn.
It has been my experience, the encoder failing to send a proper pulse count will cause most similar system faults. Replacing the servo motor (including the internal brake and encoder) is my recommendation. Although, it is possible to replace the encoder and/or repair the brake.
The information in these related post are for your informational purpose only. Omega-Star Controls & Technologies and anyone involved in making of this report, will not be liable to you in relation to the contents of, or use of, or otherwise in connection with this information contained in this report