Free C-208 Practice Questions

Question 1

A carton diverter does not move although its PLC output command and channel LED are ON. The circuit is +24 V -> sourcing output -> valve coil -> supply 0 V. During an authorized test, a qualified technician measures 24.0 V from each coil terminal to supply 0 V, but 0.0 V directly across the coil. The coil remains connected, and there are no alternate feeds. Which fault best explains this pattern?

Accepted Answer

An open return connection between the coil and supply 0 V.

Answer

An open switching element in the sourcing output channel.

Answer

An open coil winding with an intact external return conductor.

Answer

A mechanically stuck valve spool despite an intact coil circuit and proper field voltage.

Question 2

Step 20 of an indexing sequence may advance only after ClampClosed has remained 1 continuously for 2.0 seconds while that step is active. A non-retentive ON-delay timer has a 2.0-second preset and resets when its enable is false; DN is its done bit. Each scan updates the timer before testing advance, using the same sampled Step and ClampClosed values. No other logic writes the timer. Select the conditions that enforce the dwell, even if closure is delayed or briefly lost.

Accepted Answer

Enable: (Step = 20) AND ClampClosed. Advance: (Step = 20) AND DN.

Answer

Enable: Step = 20. Advance: (Step = 20) AND ClampClosed AND DN.

Answer

Enable: ClampClosed. Advance: (Step = 20) AND DN.

Answer

Enable: (Step = 20) AND ClampClosed. Advance: (Step = 20) AND (ClampClosed OR DN).

Question 3

An HMI diagnostic screen shows both Home and Extended ON for a cylinder whose end positions are mutually exclusive. The cylinder is physically extended. A live connection to the correct PLC shows Home = 0 and Extended = 1, with no input forces. The PLC data update normally, but the HMI values have a last-update time six minutes old. This screen is read-only and has no control or safety function. The best initial response to the conflicting display is to:

Accepted Answer

Investigate the HMI communication and data-update path before changing the PLC application.

Answer

Replace the two end-position sensors because their displayed states are mutually incompatible.

Answer

Take the cell out of service for a complete reload of the PLC application.

Answer

Add logic that clears Home whenever Extended becomes active.

Question 4

A technician is about to disconnect a valve line on a PLC-controlled pneumatic lift. The electrical disconnect and incoming air isolation valve are locked out. However, a fixture remains suspended by the cylinder, a cylinder-side gauge still reads 5.6 bar, and no mechanical restraint is installed. What must happen before the line is loosened?

Accepted Answer

Restrain the load with approved supports, relieve trapped pressure, and verify the line is depressurized.

Answer

Slowly crack the fitting open while a second technician watches the fixture.

Answer

Exhaust the trapped air completely, then install a mechanical support beneath the lowered fixture.

Answer

Confirm the PLC is in STOP and both valve outputs are OFF before disconnecting the line.

Question 5

Loaded testing of a 24 V DC branch gives these readings: 24.0 V at the supply, 20.0 V across the load, 0.50 A through the branch, and 4.0 V directly across one feed connector. Other wiring losses are negligible. The load requires at least 21.6 V, and its disconnected supply cable reads 24.0 V with no load attached. Which assessment correctly combines the resistance calculation with the repair decision?

Accepted Answer

8.0 ohms at the connector; repair it and repeat the loaded-voltage test.

Answer

0.125 ohm at the connector; restore it before restarting.

Answer

8.0 ohms in the load; replace the load because the supply voltage is normal.

Answer

2.0 ohms at the connector; increase the supply setting to make up the loss.

Question 6

After a software change, a Logix controller faults whenever an operator enters a recipe identifier that is not in the recipe table. The recorded major fault is a task-watchdog timeout. Code inspection finds a search loop that repeats until MatchFound becomes true, with no exit for an unmatched identifier. Which correction belongs in the application before further controlled testing?

Accepted Answer

Add a finite search bound and an explicit path for an unmatched recipe.

Answer

Increase the watchdog setting so the existing search loop has more time to finish.

Answer

Clear the major fault automatically and restart the search with the same recipe entry.

Answer

Move the unchanged search into another task that uses the same watchdog limit.

Question 7

A three-wire proximity sensor was replaced during maintenance. Its indicator responds to the target, but the PLC input no longer turns ON. The replacement is an NPN sinking sensor; the removed unit was PNP sourcing. The PLC input is sinking-only, with its common connected to supply 0 V, and the other PNP sensors on that common still work. Supply voltage and pin assignments have been verified. Which repair matches the existing input circuitry?

Accepted Answer

Fit a correctly rated PNP sourcing sensor and retain the existing common wiring.

Answer

Reconnect the shared input common to +24 V and retain all of the existing sensors.

Answer

Reverse the replacement sensor's supply leads while leaving its signal lead on the input.

Answer

Keep the NPN sensor and invert the input test in the PLC sequence logic.

Question 8

A transfer sequence remains in Retract even after the cylinder reaches its home stop. The exit condition is Home AND NOT Extended. At that moment, Extended = 0 and raw input module 2, channel 3 = 1. The approved I/O list assigns the home sensor to that channel, but the online Home alias references module 2, channel 4, whose value is 0. There are no forces. Identify the correction that addresses the blocked transition.

Accepted Answer

Correct the Home alias to reference module 2, channel 3, as documented.

Answer

Increase the retract timeout to allow additional travel time.

Answer

Invert the Home test so its present zero value permits the next sequence step.

Answer

Reposition the home sensor to hold its signal longer when the cylinder reaches the stop.

Question 9

A conveyor will not start automatically. The start-request input reaches the PLC, but the normal motor-output command stays OFF. During an authorized, guarded output-force test, the contactor picks up and the conveyor runs; removing the force stops it. No wiring or hardware was changed between these observations. What has this test established?

Accepted Answer

The downstream output and motor path can operate; the normal command logic still needs investigation.

Answer

The start request is reaching the PLC, so every automatic-start permissive has been satisfied.

Answer

The output module is defective because a forced command uses a different physical switching path.

Answer

The motor circuit has an intermittent hardware fault because operation stops when the force is removed.

Question 10

An automatic sequence may leave Idle only when a run request is present and an ordinary operator Stop circuit is healthy. Its normally closed contact produces StopHealthy = 1 when released and 0 when pressed or when the wire opens. Independent safeguards handle hazardous motion. In a Logix ladder rung, which placement of the StopHealthy test implements the required start permissive?

Accepted Answer

XIC(StopHealthy), in series with the run request.

Answer

XIO(StopHealthy), in series with the run-request condition.

Answer

XIC(StopHealthy), on a parallel branch around the run request.

Answer

XIO(StopHealthy), on a parallel branch around the run request.

Free C-208 Practice Questions

Domain 1: Use status and diagnostic indicators to troubleshoot a PLC

Question 1

Domain 2: Troubleshoot PLC inputs and outputs

Question 2

Question 3

Domain 3: Troubleshoot PLC power distribution system

Question 4

Domain 4: Troubleshoot a PLC processor

Question 5

Domain 5: Troubleshoot a PLC system with discrete I/O

Question 6

Question 7

Domain 6: Program and operate a multi-step PLC sequence program

Question 8

Question 9

Domain 7: Troubleshoot a multi-step PLC sequence program

Question 10

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