Why Your VFD Won't Start From SCADA (and How Control Words Actually Work)
A VFD is commanded through a packed control word and reports through a status word. Map either wrong and it won't start, or it clears a latched fault.
Articles
Practical SCADA notes
Field-oriented references for HMI/SCADA systems, industrial communication, alarms, tags, historians, and project delivery.
Getting Modbus RTU Through a Serial Device Server Without Dropping Frames
Commissioning a serial-to-Ethernet device server carrying Modbus RTU: operating mode, packing timers, TCP framing, idle timeouts and half-duplex control.
Building a SCADA Totalizer That Survives Counter Rollover and Meter Resets
Computing usage across a wrapping counter without inventing phantom flow: register width, correcting the delta once, and rollover versus meter reset.
One Unmapped Register Can Fail an Entire Modbus Block Read
How drivers group Modbus registers into block reads, why gap tolerance and block size matter, and how one unmapped address takes down a whole block.
Why Your Modbus Gateway Pings Fine but SCADA Still Goes Stale
A Modbus TCP-to-RTU gateway can answer ping and still drop requests. Finding the queue saturation behind stale tags, and tuning the driver for it.
Setting Modbus RTU Timing So Radios and Old Meters Actually Answer
How to choose Modbus RTU baud rate, silent interval (t3.5), and turnaround delay so slow serial devices get a fair chance to reply on a SCADA link.
How Many Modbus TCP Clients Can One PLC Actually Take?
Modbus TCP devices cap simultaneous connections lower than you think. Inventorying clients, reading real socket behaviour, and protecting the HMI.
The Modbus TCP Bug Where the Socket Is Fine but the Values Are Wrong
How a mishandled transaction ID lets a Modbus TCP gateway hand your SCADA driver the wrong register's value — and how to prove it with a capture.
When a Modbus Float Reads 1.2e-41: Getting Byte and Word Order Right
Modbus has no standard endianness for 32-bit values, so two registers can decode to garbage. Proving byte and word order on site instead of guessing.
How to Catch an Intermittent SCADA Comms Fault in a Packet Capture
Where to tap, what to filter, and how to read the first thirty seconds of a capture when comms drop and recover before anyone can get to a keyboard.
Modbus RTU Timeouts Are Usually a Wiring Problem: An RS-485 Commissioning Walkthrough
Commissioning a Modbus RTU link the right way: prove polarity, termination, biasing and grounding before you ever open the register map.
Why Your Modbus TCP Gateway Reads the Wrong Slave
The Modbus unit identifier is 'useless' on TCP until a gateway is involved. How routing works behind serial gateways, and finding the slave that answered.
Why a Successful Modbus Write Doesn't Mean the Motor Started
A Modbus TCP write response says the transaction was accepted, not that the motor moved. Command discipline: permissives, readback, and the retry trap.
Commissioning SCADA Firewall Rules: Test the Application, Not the Port
Commissioning SCADA firewall rules from data flows rather than port lists — the supporting services that break at cutover, and proving each rule for real.
Why One Slow Modbus TCP Device Can Freeze Your Whole Scan
Setting Modbus TCP poll rates, timeouts, retries and scan groups so one stalled device or saturated gateway can't drag the whole driver down with it.
Modbus Exception Codes: The Device Answered, It Just Said No
Reading Modbus exception responses on the wire, telling a refused request from a dead link, and chasing illegal-address and gateway causes.
A Clean Modbus Poll Can Still Show the Wrong Number: Commission the Register Map First
Modbus connects, unit IDs respond, polls complete — and the operator still reads a swapped float. Proving a register map before the historian trusts it.
SCADA Network Troubleshooting Checklist
A layered checklist for troubleshooting SCADA communication problems from physical link to protocol behavior.
From SCADA Signals to Operational State
How raw SCADA, HMI and protocol values become useful machine state, process state, alarm state and control state, and where each one is decided.
Modbus TCP Basics
A concise practical guide to Modbus TCP concepts: clients, servers, unit IDs, function codes, registers, polling, and mapping pitfalls.