Forcing an Input on a ControlLogix, and Being Certain You Removed It
Install a force on a 1756-L83E, enable it, then prove it is gone: the three FORCE indicator states, the GSV that reads force status, Remove vs Disable.
ControlLogix
Discrepancy Time on a Dual-Channel Safety Input: What It Protects and How to Pick It
Pick a discrepancy time for a 1791ES dual-channel input from the device that drives it, know which setting the DCS instruction sees, and clear the fault.
Reading a CompactLogix Tag from a Raspberry Pi with pycomm3
Four lines of Python on a Raspberry Pi 4 read a CompactLogix tag – a REAL out of a 5069-L306ER – and nothing at either end is licensed. pycomm3 1.2.16 speaks EtherNet/IP to TCP port 44818 itself, which takes the OPC server, the Windows box it used to live on and the licence out of … Read more
A MSG Instruction That Actually Works: Path, Type and the Error Codes
16#0204 appears twice in the same Rockwell reference manual with two different meanings, and which of the MSG instruction error codes tables you are reading decides where you spend the next hour. In the extended error codes for error 0001 it is Unconnected message timeout. In the module fault codes it is Connection Request Error: … Read more
Two PLCs, One Tag: Produced and Consumed Tags on ControlLogix
Produced and consumed tags stop at 500 bytes, and at 480 once the data crosses a network, because the transfer spends 20 of them on overhead. Try to produce an INT array and Logix Designer refuses: DINT, UDINT, LINT, ULINT, REAL and LREAL are the atomic types that go across on their own, and anything … Read more
Adding a Generic EtherNet/IP Module to the Ethernet Card: Connection Parameters and RPI
Assembly instances, sizes, Comm Format and RPI for a device with no catalogue profile and no EDS file, plus the connection error codes that follow.
Commanding a PowerFlex 525 from a ControlLogix: The Command Word, the Reference and the Status Bits
Bit 0 of the PowerFlex 525 logic command word is Normal Stop, and it has to be sitting at 0 before bit 1 will ever start the drive. That footnote under the table in Appendix D of 520COM-UM001 is behind most of the drives that show a green connection in the I/O tree and still … Read more
PLC Hardware Components and the Software That Uses Them
What is in a PLC rack and how the software sees it: power supply budget, CPU memory, I/O cards, tasks and routines, and tags against S7 addresses.
Common PLC Programming Mistakes: Six That Cost Hours
A TON with a .PRE of 5000 that sits in a subroutine only called in Auto, with its rung left true, is already done on the first scan back after twenty minutes in Manual. Publication 1756-RM018A-EN-P prints the arithmetic that explains it, ACC = ACC + (current_time – last_time_scanned), so the timer bills the whole … Read more
Wellhead ESD Logic and RTU Polling on a Remote Pad
Wellpad controller choice, an ESD permissive rung that will not auto restart, Modbus poll budgets over radio, flow computers and tank farm level control.
How to Create a Project in Studio 5000 (Step by Step, v33)
Create a new Studio 5000 Logix Designer project the right way: pick the controller, match the firmware revision, add I/O, write the first rung, download and go online.
PLC vs DCS Programming: Where the Two Part Ways
PLC vs DCS programming compared by an engineer who works on both: tags and rungs against loops and blocks, redundancy, alarms, batch and real cost.
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