Mission 89 · PRO

One alarm block for every alarm: PLC SCADA training exercise

New, seen, cleared: one loop takes every alarm through the same states and marks the one that came first.

Write the alarm block behind the factory's alarm list: one loop that takes each of five alarms through new, seen and cleared, counts what is active and unacknowledged, reports the top priority and marks the alarm that came first.

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Every Coaching lesson, from zero
Every mission and lesson, as you level up
A practical test for every title, with a certificate
Rewind any test, one scan at a time
Worked solutions when you're stuck
The code converter, as much as you like

The 3D model factory this mission runs on

Level: Expert
Time: About 45 min
Reward: +800 XP
Rig: 3D model factory
Siemens editors: SCL
Rockwell editors: Structured Text
Beckhoff editors: Structured Text
Stage: 44. SCADA 2: one alarm block for every alarm

Required behaviour

One alarm block for every alarm: what your code must do

The plant control, the five alarm conditions Cond[0] to Cond[4] and their priorities Prio[0] to Prio[4] are written. Write one FOR loop over the five alarms that keeps AlarmState[0] to AlarmState[4]: 0 Normal, 1 New (active, not acknowledged), 2 Seen (active, acknowledged), 3 Cleared, not seen. From 0, the condition coming on gives 1. In 1, a press of Ack gives 2; the condition going off gives 3. In 2, the condition going off gives 0. In 3, a press of Ack gives 0; the condition coming back gives 1. Each alarm makes at most one move a scan, and Ack acts on the press, not while it is held. ActiveCount is how many alarms are in state 1 or 2. UnackCount is how many are in state 1 or 3. TopPriority is the most urgent priority among the alarms not in state 0: 1, 2 or 3, or 0 for none. FirstOut is the number of the alarm that started the trouble, counting from 1: when an alarm leaves state 0 while FirstOut is 0, FirstOut becomes its number. If two start in the same scan, the one earlier in the table wins. FirstOut goes back to 0 only when every alarm is in state 0 again. On the Operator screen tab, choose how the list treats a cleared alarm, the first alarm and the states.

States: 0 Normal, 1 New, 2 Seen, 3 Cleared, not seen.
Ack: On the press: 1 becomes 2, and 3 becomes 0.
Totals: ActiveCount: states 1 and 2. UnackCount: states 1 and 3. TopPriority: the most urgent not in 0.
First out: Set by the first alarm to leave 0; cleared when all are 0 again.

Tag table

One alarm block for every alarm: inputs and outputs

Your program reads 19 inputs and sets 20 outputs. One more input drives the simulation or shows a reading, for you to test with. The names are the same in every maker’s editor.

Tag	Data type	Your code	What it means on the machine
`Start`	`BOOL`	ReadsAn input your code needs	Start the factory
`Stop`	`BOOL`	ReadsAn input your code needs	Stop the factory where it is
`Reset`	`BOOL`	ReadsAn input your code needs	Reset after an emergency stop or a light-curtain trip
`EStop`	`BOOL`	ReadsAn input your code needs	Emergency stop pressed
`CompressorFault`	`BOOL`	ReadsAn input your code needs	Try it: the compressor trips
`AirPressure`	`REAL`	ReadsAn input your code needs	Air receiver pressure, bar
`SteamPressure`	`REAL`	ReadsAn input your code needs	Boiler steam pressure, bar
`VesselLevel`	`REAL`	ReadsAn input your code needs	Mixing vessel level, %
`VesselTemp`	`REAL`	ReadsAn input your code needs	Batch temperature, °C
`SugarAdded`	`REAL`	ReadsAn input your code needs	Sugar the weigh feeder has added to this batch, kg
`BufferLevel`	`REAL`	ReadsAn input your code needs	Filler buffer tank level, %
`BadBottle`	`BOOL`	ReadsAn input your code needs	Camera: a bottle with no label is passing
`GateEye`	`BOOL`	ReadsAn input your code needs	A bottle is in front of the reject gate
`AccumFull`	`BOOL`	ReadsAn input your code needs	Three packs are waiting for the robot
`CurtainClear`	`BOOL`	ReadsAn input your code needs	Light curtain beams unbroken
`PalletFull`	`BOOL`	ReadsAn input your code needs	A full pallet is waiting or on its way to the wrapper
`PalletOnWrapper`	`BOOL`	ReadsAn input your code needs	A pallet is on the wrapper turntable
`WrapDone`	`BOOL`	ReadsAn input your code needs	The pallet on the wrapper is wrapped
`Ack`	`BOOL`	ReadsAn input your code needs	Screen button: acknowledge the alarms
`PersonInCell`	`BOOL`	Not neededFor testing or watching; your code can leave it out	Try it: someone walks into the robot cell
`Compressor`	`BOOL`	WritesAn output your code sets	Run the air compressor
`BoilerOn`	`BOOL`	WritesAn output your code sets	Switch the boiler on
`WaterValve`	`BOOL`	WritesAn output your code sets	Water into the mixing vessel
`Feeder`	`BOOL`	WritesAn output your code sets	Run the sugar weigh feeder
`Agitator`	`BOOL`	WritesAn output your code sets	Run the agitator
`SteamValve`	`BOOL`	WritesAn output your code sets	Steam to the vessel jacket
`TransferPump`	`BOOL`	WritesAn output your code sets	Pump the batch to the buffer tank
`LineRun`	`BOOL`	WritesAn output your code sets	Run the bottling line
`RejectGate`	`BOOL`	WritesAn output your code sets	Fire the reject gate
`RobotEnable`	`BOOL`	WritesAn output your code sets	Let the robot palletise
`PalletOut`	`BOOL`	WritesAn output your code sets	Move the full pallet to the wrapper
`Wrap`	`BOOL`	WritesAn output your code sets	Run the stretch wrapper
`AGVCall`	`BOOL`	WritesAn output your code sets	Call the AGV to collect the wrapped pallet
`GreenLamp`	`BOOL`	WritesAn output your code sets	Stack light: producing
`AmberLamp`	`BOOL`	WritesAn output your code sets	Stack light: starting or waiting
`RedLamp`	`BOOL`	WritesAn output your code sets	Stack light: emergency stop or light-curtain trip
`ActiveCount`	`INT`	WritesAn output your code sets	Alarm list: alarms whose condition is on
`UnackCount`	`INT`	WritesAn output your code sets	Alarm list: alarms nobody has acknowledged
`TopPriority`	`INT`	WritesAn output your code sets	Alarm list: most urgent priority showing, 1 to 3, or 0
`FirstOut`	`INT`	WritesAn output your code sets	Alarm list: the alarm that came first, 1 to 5, or 0

In Siemens SCL, write a block’s own tags with # in front, as TIA Portal does: #Start. Rockwell and TwinCAT use the name on its own: Start.

Automatic tests

One alarm block for every alarm: what the tests check

Every alarm follows the same four states: 0 Normal, 1 New, 2 Seen, 3 Cleared, not seen.
An alarm that clears before Ack stays on the list as 3 until Ack; one that comes back before Ack is New again.
Ack acts on the press: a held Ack does not acknowledge an alarm that arrives later.
ActiveCount, UnackCount and TopPriority match the list on every .
FirstOut names the alarm that came first and holds it until the list is empty.
The list keeps a cleared alarm until it has been seen, marks the first one and says each state in words.

Try it Use the buttons below the model and watch the rig respond.
Test solution Every check runs on your code in one press.
Rewind PRO (needs Pro) If one fails, step back through it one scan at a time to see why.

Stuck on this mission? Ask the members in the Locker Room.

Why it matters

Where you’d see this on site

A plant's SCADA server holds one alarm table, each line with a state, a priority and a time. The first out mark is what the day shift reads after a night of stops.

One trip can raise twenty alarms in a few seconds. Without states and a first out mark, the operator acknowledges them all to silence the horn and the cause is lost.

Where you'd find thisOne controller for a whole factory: when each machine may run, and what keeps it safe

A small drinks factory makes an orange drink. Sugar and water are batched and pasteurised, then pumped to a filler. Bottles are filled, capped, labelled and inspected, packed in sixes, stacked on pallets by a robot, wrapped and carried to the dock by a driverless forklift. Every machine has its own controls; the plant controller decides when each may run, hands work from one to the next, and stops everything safely.

BatchMix and pasteurise
FillFill, cap, label
InspectReject bad bottles
PackRobot stacks packsYou are here
ShipWrap, AGV to dock

On a real site: places, parts and safety

Soft drinks and juice bottling halls
Sauces, dairy and liquid food plants
Household and personal-care liquids

An emergency stop is wired through a safety relay that cuts the power on its own. The program must then hold everything off and wait for a deliberate Reset and Start, so nothing moves by surprise.

Robot cells are fenced. Light curtains and interlocked doors stop the robot when someone goes in, and a restart needs a reset from outside the cell, in the spirit of ISO 10218 and ISO 13849.

The sizes, timings and cutaways are teaching choices, not a drawing of any one real installation.

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