Every PLC and HMI tutorial on plctr.com: project setup, ladder and structured text, communication, troubleshooting and commissioning, written from the plant floor.
JSR, SBR and RET: Passing Parameters Into a Routine Without a Controller Tag Type 4, Code 31 on a 1756-L83E, and the routine it pointed at was three rungs long. The general instructions reference gives three separate ways to earn that code and every one of them is about counting: a JSR with fewer input … Read more
FAL and FSC Over an Array: the Control Tag, the Position and the Scan It Takes An FSC with a Length of 10 found its mismatch at element 3 on a 1756-L83E and then stopped looking. .FD was 1, .POS was 3, .IN was 1, and elements 4 through 9 were never compared — not … Read more
The MSG Control Tag on a Logix Controller: What Each Tab Writes Into It Line_Msg.DN came true on rung 13 of a 1756-L71 and the forty DINTs the rung was guarding still held last shift’s numbers. The bit had been set by a different message — a four-element write to a capper down on rung … Read more
COP and CPS Instructions on a ControlLogix: Which One Copies What A COP with a Length of 20 moved five bytes. The source was Packer_Raw, a SINT[5]; the destination was Packer_Scaled, a DINT[10]; the rung went true on every scan of a 1756-L71 and nothing faulted, nothing latched, nothing appeared in the Minor Faults tab. … Read more
The scope says twelve bays, a MiCOM C264 in each cubicle, a gateway to the control centre, and an SCD file that the protection engineer will issue in week six. There is no ladder anywhere in it, no tag database you recognise, and no download button of the kind you have been pressing for fifteen … Read more
The numeric display is assigned {::[CLGX]Program:Packer.Bag_Count}, the value counts up all afternoon while the application is tested on a laptop, and the PanelView Plus 7 bolted to the machine shows four dashes. The tag is not the problem. The shortcut called CLGX carries two communication paths that are configured in two different places, and the … Read more
A new SM 1223 goes into slot 2, the panel comes back up, and the ERROR LED flashes red while the STOP/RUN LED sits solid yellow. The module that came out was 6ES7223-1BL32-0XB0. The one from stores is 6ES7223-1BL32-1XB0, and those two part numbers are the same sixteen inputs and sixteen outputs in the same … Read more
FB120 carries the orange half-circle in the project tree and the block you have open is the one you wrote on Tuesday. On an S7-1500 that symbol is the result of a checksum comparison, not a time stamp comparison, and the manual lists more than a dozen separate checksums behind it. Three of them have … Read more
The batch record says the mixer started at 06:14 and the operator watched it start at 07:14, on the Sunday the clocks moved. The CPU 1516-3 PN/DP is keeping perfect time. What is wrong is that somebody wired RD_SYS_T into the timestamp and RD_SYS_T hands back the module time, which on this family is always … Read more
MOVE_BLK with COUNT := 20 aimed at an ARRAY[1..10] of Real on a CPU 1516-3 PN/DP does not put the CPU in STOP and does not hand you an error in the diagnostics buffer. The enable output drops to 0, and on a box inserted with the editor’s default settings there is no ENO pin … Read more
The display reads TORQUE TRIP CLOSED, the IQ40 on the raw water isolation valve has stopped short of its closed limit, and the operator has pressed close four more times with nothing happening. That second part is not a fault: PUB002-040 says that once the actuator meets its set torque between the limits it stops … Read more
The servo-on command is made, the drive display sits at b01 or its axis number, RD never comes on and the machine will not start its home position return. No alarm, no warning, nothing flashing. A Mitsubishi servo home position that refuses to set is almost never the servo’s fault, and on an MR-J4-A configured … Read more