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Mission 34 · Pro function block and AOI exercise

Call one block for two pumps

One block, two copies, each with its own memory.

Call the ready-made PumpControl block every , once as DutyControl and once as StandbyControl. Each is an instance: a copy of the block with its own memory. Start latches PumpOn on. StandbyStart latches StandbyPump on. Each works on its own. Stop, or losing Permit, stops both pumps. Fault stops only the duty pump, and StandbyFault only the standby pump. Each instance reports Running and Starts in DutyStatus and StandbyStatus.

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The 3D pump skid this mission runs on Pro mission
Test replay

Independent instances and held pushbuttons

Test 1 of 3
Set by the testChecked by the testStep 5 of 5 · 1.1 s
Level
Advanced
Time
About 20 min
Reward
+300 XP
Rig
3D pump skid
Siemens editors
SCL
Rockwell editors
Structured Text
Course stage
20. Reuse tested control logic
Automatic tests

What the tests check

  1. DutyStatus.Starts and StandbyStatus.Starts count each pump’s starts, not scans. DutyStatus.Running matches PumpOn. StandbyStatus.Running matches StandbyPump.
  2. PumpOn and StandbyPump each stay on after Start or StandbyStart is released.
  3. Call the block even when Stop, Fault or Permit says stop. Skipping the call does not stop the pump.
  1. Try it Use the buttons below the model and watch the rig respond.
  2. Test solution Every check runs on your code in one press.
  3. Replay If one fails, step through it one scan at a time to see why.
Why it matters

Where you’d see this on site

A factory has two water pumps, each with its own buttons but the same Start and Stop rules. Each pump needs its own memory.

Shared memory can make starting one pump affect the other. Separate memories let each pump respond to its own buttons and fault.

Where you'd find thisWater for the top floors

In a block of flats, a basement tank holds water from the mains. Two pumps push it up to the taps above. One runs while the other waits as a spare. A low-water switch stops the pumps before the tank runs dry.

  1. Street mainsWater enters the building
  2. Storage tankHolds a supply for the pumps
  3. Water pumpsPush water to the floors aboveYou are here
  4. Taps upstairsResidents use the water they need
On a real site: places, parts and safety
  • Block of flats — pushing water up to the top floors
  • Brewery — sending hot water to a brewing tank
  • Water-treatment works — moving water between filter tanks
  • Office building — pumping water round the heating pipes

A low-water switch can take away permission to run. The pump must stop before it runs dry and damages its seal.

The PLC can say ON even when a pump has failed. Check the measured flow as well as the command.

The Stop input in these exercises is not an emergency stop. Real machines also need guards, emergency stops and a safe way to cut the power.

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

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