Free C-307 Practice Questions

Question 1

Six PNP proximity sensors share a 24 V DC PLC input group whose common is connected to 0 V. A seventh sensor must be NPN; its output switches to 0 V when actuated. The card allows sourcing or sinking inputs, but all channels in a group share one common. A second, independently configurable group is unused. Which connection accommodates the NPN sensor while preserving the six working inputs?

Accepted Answer

Connect the NPN sensor to the unused group, with that group's common connected to +24 V.

Answer

Keep the occupied group's common at 0 V and invert the NPN channel's input logic in software.

Answer

Connect the NPN sensor to the unused group, with that group's common connected to 0 V.

Answer

Change the occupied group's common to +24 V and connect the NPN output to that group.

Question 2

A PLC reliably reads a VFD's speed-feedback holding register over Modbus RTU. A new function 03 request for six registers beginning at protocol address 200 receives a valid exception 02 response. The drive's register map lists readable holding registers at addresses 200 through 203; addresses 204 and 205 are not implemented. What change resolves this request error?

Accepted Answer

Reduce the requested quantity from six registers to four.

Answer

Reverse the RS-485 data pair and repeat the six-register request.

Answer

Increase the response timeout while retaining the same address and quantity.

Answer

Change the request from function 03 to function 04.

Question 3

Following a VFD shutdown, a qualified technician locks out all supplies and completes the required restart checks. The manufacturer's access procedure requires a wait of at least 10 minutes and a DC-bus reading below 50 V at designated test points. After 12 minutes, an appropriate, verified meter reads 72 V DC; the display is dark. What should govern access to the bus terminals?

Accepted Answer

The measured bus voltage, which remains above the permitted access threshold.

Answer

The elapsed waiting time, because the manual's minimum has been exceeded.

Answer

The dark display, because the drive has no remaining control power.

Answer

The failed restart attempt, because motor operation has been prevented.

Question 4

A calibrated source is connected to a passive PLC current input, and the PLC reports each injected current correctly. The HMI should convert a linear 4-20 mA signal into 0-200 °C, but it displays 40 °C at 4 mA, 120 °C at 12 mA, and 200 °C at 20 mA. Which conversion error would produce all three readings?

Accepted Answer

The HMI maps 0-20 mA linearly to 0-200 °C.

Answer

The HMI maps 0-16 mA linearly to 0-200 °C.

Answer

The HMI maps 4-24 mA linearly to 0-200 °C.

Answer

The HMI adds a 40 °C offset after correct 4-20 mA scaling.

Question 5

An HMI passes its functional checks, but a gap remains under one corner of its front bezel. Its mounting instructions allow at most 0.5 mm deviation from a flat sealing surface and specify 0.2 N·m clip torque. The cutout and wall thickness meet specification. At the gap, the wall is bowed by 0.9 mm; the gasket is undamaged and every clip is at the specified torque. Which action addresses the sealing defect?

Accepted Answer

Restore the mounting surface's flatness, then refit the HMI using the specified clip torque.

Answer

Accept the seal because both mounting torque and functional checks are correct.

Answer

Increase torque at that corner until the bezel pulls the distorted enclosure wall firmly against the gasket.

Answer

Fit a second gasket to take up the gap in the enclosure wall.

Question 6

A PLC's isolated relay output must command a VFD to run when the relay energizes and stop when it releases. The drive diagram identifies P24 as its +24 V control source, DI1 as RUN when connected to P24, and DCOM as its control return. The relay has COM, NO, and NC contacts but supplies no voltage. The PLC and drive use separate 24 V supplies whose returns are not connected. Select the correct wiring.

Accepted Answer

Drive P24 to relay COM; relay NO to drive DI1.

Answer

PLC +24 V to relay COM; relay NO to drive DI1.

Answer

Drive P24 to relay COM; relay NC to drive DI1.

Answer

Drive DCOM to relay COM; relay NO to drive DI1.

Question 7

A pair of rubber-insulating gloves has remained properly stored in its unopened original packaging since passing the manufacturer's electrical test nine months ago. The package is opened for the first time today; inspection and the air test pass. The glove class and protector gloves are suitable for the assigned task. Under OSHA 29 CFR 1910.137, what does the nine-month test age mean for first issue?

Accepted Answer

First issue is permitted; the factory test is less than 12 months old.

Answer

Retest before issue because electrical testing must occur on the day of first use.

Answer

First issue is permitted; the air test restarts the electrical-test interval.

Answer

Retest before issue because the six-month interval applies from the factory test.

Question 8

A 45 m Cat 5e cable for a 100BASE-TX HMI link passes a simple continuity test: pin 1 connects to pin 1, continuing through pin 8, with no shorts. Both plugs place the green pair on pins 3 and 4 and the blue pair on pins 5 and 6; the other pairs follow T568B. The link is unreliable. Which repair addresses the wiring defect?

Accepted Answer

Reterminate both ends to T568B: green pair on 3/6, blue pair on 4/5.

Answer

Keep the existing wire map and replace the plugs with bonded, shielded types.

Answer

Cross pins 1/2 with pins 3/6 at one end to exchange the transmit and receive pairs.

Answer

Keep the existing wire map and force both ports to 100 Mb/s, full duplex.

Question 9

A VFD accepts the PLC's terminal RUN command with no fault or active inhibit, yet its commanded-frequency monitor stays at 0.0 Hz. The PLC's speed output measures 6.0 V at AI1, which is correctly configured for the 0-10 V signal. The selected command source is terminals; the selected speed-reference source is keypad, set to 0.0 Hz. With the machine secured for the authorized motion test, which correction restores PLC speed control?

Accepted Answer

Select AI1 as the speed-reference source and retain terminal control of RUN.

Answer

Select keypad control for both RUN and speed.

Answer

Raise the minimum frequency until the motor turns whenever the terminal RUN command is asserted.

Answer

Rescale AI1 so that 6.0 V corresponds to the drive's maximum frequency.

Question 10

A transmitter reads the correct temperature with a Pt100 simulator connected directly at its terminals. Moving the same simulator to the sensor end of the three-wire field cable introduces an error that changes as the cable warms. Terminal assignments are correct. This transmitter's compensation requires equal resistance in leads L1 and L2; isolated cable measurements are 4.0 Ω and 1.0 Ω, respectively. Two-wire mode is also supported. The appropriate repair is to:

Accepted Answer

Replace the field cable with matched three-conductor cable, then retest.

Answer

Apply a fixed zero offset for the present error.

Answer

Select two-wire mode and connect the spare terminal as required for two-wire operation.

Answer

Increase the transmitter's damping time.

Free C-307 Practice Questions

Domain 1: adhering to electronic installation safety rules

Question 1

Domain 2: using proper PPE

Question 2

Domain 3: reading wiring installation diagrams with PLCs/HMIs/VFDs

Question 3

Question 4

Domain 4: cabinet mounting PLCs/HMIs/VFDs

Question 5

Domain 5: wire routing and grounding PLCs/HMIs/VFDs

Question 6

Domain 7: installing Modbus and Ethernet communications network

Question 7

Question 8

Domain 8: installing analog input transmitters and analog sensors

Question 9

Question 10

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