PLC & HMI

Every PLC and HMI tutorial on plctr.com: project setup, ladder and structured text, communication, troubleshooting and commissioning, written from the plant floor.

ESTOP and Its Two Reset Inputs: What a Safety Reset Actually Requires

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The ESTOP instruction drawn as a panel of operands and values: Reset Type Manual with the note that Automatic energises Output 1 after 50 ms, Channel A on IN0 and Channel B on IN1 both normally open with safe equal to zero, Circuit Reset on IN2 where a zero to one transition energises Output 1, Fault Reset on IN3 where a zero to one transition clears Inputs Inconsistent, an Inconsistent Time Period of 500 ms marked fixed with no operand for it, and the outputs Output 1, Cycle Inputs, Circuit Reset Held On, Inputs Inconsistent and Fault Present with what each one means

ESTOP and Its Two Reset Inputs: What a Safety Reset Actually Requires An ESTOP instruction on a GuardLogix 5580 sitting with Fault Present on and Inputs Inconsistent on will ignore the blue button on the panel for as long as that button is wired to the Circuit Reset operand. Circuit Reset energises Output 1, Fault … Read more

Writing Your First Safety Routine: Standard Tags, Safety Tags, and the Mapping Between Them

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Three boxes across the top showing which way data crosses: Standard task on the left holding standard controller tags, standard program tags and the note that HMI and MSG write here; Safety tag mapping in the middle, reached from Logic then Map Safety Tags, one standard tag to one safety tag copied at task start; Safety task on the right holding safety controller tags and safety program tags written only by safety logic. A return path along the bottom is labelled that standard routines read controller-scoped safety tags directly with no mapping needed. Below, a panel listing the five rules that decide whether a mapping pair is legal and the five states in which mapping is refused outright

Writing Your First Safety Routine: Standard Tags, Safety Tags, and the Mapping Between Them Put a standard BOOL on a rung inside a safety routine and Studio 5000 will not accept it; the browse list does not even offer the tag. Try the obvious workaround next and the software refuses that too, because you cannot … Read more

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

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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

The Safety Task on a GuardLogix: What Runs In It, What Cannot, and How to Pick the Period

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Safety Task Properties drawn as a panel of fields and values: Task type Periodic fixed, Period 20 ms with the range 2 to 500 ms and the note that it cannot be edited online, Priority 1 recommended, Watchdog 20 ms with the range 2 to 500 ms and the requirement that it be less than or equal to the period, one safety task per controller that cannot be deleted, routine language Ladder Diagram only, and the resettable maximum observed scan time

The Safety Task on a GuardLogix: What Runs In It, What Cannot, and How to Pick the Period The Safety Task Properties dialog on a GuardLogix 5580 takes a period between 2 and 500 ms and a watchdog between 2 and 500 ms, and the safety reference manual is explicit that the watchdog has to … Read more

Comparing REAL Values on a ControlLogix: Why EQU Is the Wrong Instruction

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Table of five decimal values against what a Logix REAL actually stores for each, including 10.1 minus 10.0 and 0.1 accumulated 1850 times

Comparing REAL Values on a ControlLogix: Why EQU Is the Wrong Instruction Page 882 of 1756-RM018A carries a worked example nobody quotes: subtract 10 from 10.1 on a Logix controller and the result could very well be 0.10000038, rather than the 0.1 you were expecting. Two pages of guidance later the same manual puts it … Read more

Kepware with a ControlLogix: the Tag Import, the Arrays, and What Breaks

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Five boxes in a row from Studio 5000 through the import route, the server group and the server tag to the client item, with four numbered red points marking where each join fails

Automatic tag generation against one 1756-L83E produced 5537 server tags in about ninety seconds, and the clients on that site reference 684 of them. The other 4853 are array elements nobody reads, structure members nobody reads, and a full PID_ENHANCED nobody has looked at since commissioning. They cost project load time, they cost browse time … Read more

RMPS and RLIM on a ControlLogix: Ramping a Setpoint Instead of Stepping It

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Trend of a setpoint written as a step from 20 to 75 percent against the same setpoint rate limited at 5.0 per second, with the drive current limit marked

RMPS and RLIM on a ControlLogix: Ramping a Setpoint Instead of Stepping It A sequence step writes 75.0 into the speed reference of a PowerFlex on a packing line that was sitting at 20.0, and the drive comes back with an overcurrent on acceleration about 400 ms later. Nothing in the controller did anything wrong. … Read more

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

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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

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