Articles - PLC Programming & Automation

Scan Rates, Scan Groups and the Deadband That Halves Your Traffic

by PLC

A four-column table listing the controller task, the device Scan Mode, the tag Scan Rate and the client group rate against what each controls, its range and when it wins, with the device Scan Mode rows highlighted

A SCADA client on the TR-14 line subscribes to 1180 tags in one group at 250 ms, which people write down as 4720 value updates a second. Over an hour the server actually delivered 3,832,580 notifications, and 3,744,000 of those came from 260 analogue tags, most of which were sitting still. The 920 digital and … Read more

Kepware Channels, Devices and Tags: the Structure to Get Right Before the First Tag

by PLC

Five boxes in a row showing one value walking from the controller through the channel, the device, the tag group and the server tag, with four numbered red points below marking where the chain breaks

A SCADA client stores one string for every value it reads, and on the line I am about to describe that string is CLX_Line1.Bagger.Infeed.Belt1_Run. Four names, each chosen by a different person on a different day, and 684 more strings on that one device built the same way. Rename the tag group on a Friday … Read more

Functional Safety PLC: Risk Assessment to PLd Architecture

by PLC

Timing chart of a guard door safety function: the door opens, the safety function result drops shortly after, the contactors release inside the response time budget, and the output only returns after a manual reset pulse with the door closed

How functional safety works on a PLC job: the ISO 13849-1 risk graph, PLr, category 3 architecture, MTTFd, DC, CCF, a PFHd budget and SISTEMA.

PLC Programming for Beginners: Your First Working Project

by PLC

Ladder rung with Start in parallel with the Conveyor seal-in contact, in series with a normally closed Stop contact and a normally closed Overload contact, driving the Conveyor output coil

PLC programming for beginners without the theory dump: pick a simulator, write a start/stop rung, add a timer and a counter, wire one HMI button.

Wireless PLC Communication: Wi-Fi, Radios and Cellular

by PLC

Timing chart of a wireless link: the radio link drops, I/O data stops arriving, the connection fault bit sets after the timeout window expires, the line stops, and everything recovers only after the link returns and the logic is reset

Wireless PLC communication done properly: choosing Wi-Fi, 900 MHz radios or cellular, RPI and timeout budgets, antennas, roaming, and link loss logic.

PLC Hardware Components and the Software That Uses Them

by PLC

Timing chart showing a field input rising, the input image bit following at the next input scan, the coil in logic changing during the program scan, and the physical output finally switching after the output scan, about one scan behind the field

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.

PLC Motor Control VFD Setup: DOL, PowerFlex 525, G120

by PLC

Ladder rung: Start in parallel with the Run_Cmd seal-in contact, in series with a normally closed Stop and a Drive_Ready contact, driving the Run_Cmd output

Choose DOL or a drive, wire the stop so it works without the PLC, set the drive parameters and tags, then read the fault codes when it trips.

PLC HVAC Control: An Air Handler Sequence That Holds

by PLC

Timing chart of an air handler start: occupied signal, outside air damper to minimum, supply fan running, and the cooling loop enabled after the delay

Write an AHU sequence on a CompactLogix: damper minimum position, supply fan VFD, chilled water PID, economizer changeover, compressor staging and BACnet.

PLC Program Documentation That Survives a Night Call

by PLC

Ladder rung showing a filler conveyor motor start/stop with seal-in and descriptive tag names L3_FIL_Start_PB, L3_FIL_Stop_PB, L3_FIL_Mtr_OL and L3_FIL_Mtr_Run

Tag naming, rung comments, UDT and AOI descriptions, pass-through and L5X exports that keep a Studio 5000 or TIA Portal project readable years later.

Textile Warper and Stenter: Draw Ratio and Break Stops

by PLC

Ladder rung for the yarn break latch: Break_Sensor examined on with a parallel Break_Latched seal-in branch, in series with Reset_PB examined off, driving the Break_Latched output coil

What a warper, a sizing line and a stenter need from a PLC: draw ratios, dancer and load cell loops, yarn break stops and recipes on S7-1500 or Logix.

Injection Molding Cycle, Barrel Zones and Guard Interlocks

by PLC

Timing chart of one 22.5 s molding cycle: clamp locked from 1.5 s to 18.2 s, injection from 2 s to 3.2 s, hold pressure from 3.2 s to 6.2 s, cooling timer from 6.2 s to 18.2 s with screw rotation from 6.2 s to 12.7 s, mold open position reached at 20.2 s, ejector forward from 20.4 s to 21.4 s, mold closing again at 22.5 s and locked at 24 s

Injection molding from the controls side: the cycle as a state machine, barrel zone PID and thermocouple checks, EUROMAP 67 and 77, guards, and rubber.

The 5 PLC Programming Languages and When to Use Each

by PLC

Ladder rung with Start_PB XIC, seal-in branch on Conv_Run, Stop_PB XIO and Guard_OK XIC driving the Conv_Run OTE coil

Ladder, FBD, Structured Text, SFC and IL compared on real hardware: what Studio 5000 v33 and TIA Portal V18 support, and which one to pick per job.

Advertisement