Installation, Configuration & Troubleshooting Flashcards

An integrator is configuring a redundant PLC system. Which mechanism ensures automatic failover to the standby CPU without losing the current process state?

Answer: Hot standby with continuous state synchronization between primary and secondary CPUs

Hot standby redundancy continuously mirrors process data and I/O state to the secondary CPU, enabling bumpless automatic failover without process interruption.

During commissioning, an integrator needs to verify that all emergency stop (E-stop) circuits function correctly. The proper test method is:

Answer: Physically actuate each E-stop device and verify the expected safe state is achieved in the machine

Safety standards (IEC 60204-1) require physical functional testing of every E-stop device to confirm the machine reaches a safe state when actuated.

A network switch in a control cabinet shows a port LED that alternates between amber and green. In most managed industrial switches, this indicates:

Answer: A duplex or speed mismatch causing half-duplex operation and excessive collisions

Alternating amber/green on many industrial switch ports indicates a duplex mismatch, where one end auto-negotiated differently, causing collisions and degraded throughput.

A system integrator must set the IP address on a device that has no display and only a rotary address switch. If the switch is set to position 12 (0x0C), and the base network is 192.168.1.x, the resulting IP address is:

Answer: 192.168.1.12

Rotary address switches set the host octet; position 12 in decimal maps directly to the last octet, giving 192.168.1.12.

An integrator encounters a PLC program that uses a TON (timer on-delay) instruction, but the timer never reaches its preset. The most probable cause is:

Answer: The timer enable (EN) bit is being reset before the accumulated value reaches the preset

If the enable rung goes false before accumulation completes, the TON resets its accumulated value and the done bit is never set.

When installing shielded instrumentation cable between a sensor and a control panel, the cable shield should be:

Answer: Connected to earth ground at one end only (typically the panel end)

Single-end grounding of the shield at the panel (control) end prevents ground loop currents that would introduce noise into the signal, while still providing EMI shielding.

A system integrator performing a site acceptance test (SAT) discovers that a flow meter reads accurately in the lab but shows a constant 8% high reading in the field. The most likely reason is:

Answer: The flow meter is not installed with the required straight pipe run (upstream/downstream)

Flow meters require straight pipe runs upstream and downstream to ensure a developed flow profile; without them, flow distortions cause consistent positive or negative errors.