Chapter 10, 12 , 13

Refer to the circuit shown in Figure 11-23. Name two methods of changing the amount of time delay.

Change RT or the capacitor value or C1

An off-delay timer's contacts change to their energized state after the delay.

False

Which of the following might cause the N.O. contact of a timer relay to be closed whether the coil is energized or not?

Mechanical problem with the timer relay

In the control circuit shown in Figure 12-2, if an overload occurs on any motor, all three motors will stop running. Using a separate sheet of paper, redesign the circuit so that the motors must still start in sequence from #1 to #3, but an overload on any motor will stop only that motor. If an overload should occur on motor #1, for example, motors #2 and #3 would continue to operate.

Move the overload contacts to right after each coil

Name two methods used by electronic timers to obtain their time base.

RC time circuit or quartz clocks

Refer to the circuit shown in Figure 10-9. In this circuit the jog push button has again been connected incorrectly. The normally closed section of the button has been connected in series with the normally open run push button and the normally open section of the jog button is connecting in parallel with the holding contacts. Explain how this circuit operates.

The M contact energizes and continues to provide current regardless of the jogging button

Refer to the circuit shown in Figure 10-8. In this circuit, the jog button has been connected incorrectly. The normally closed section has been connected in parallel with the run push button and the normally open section has been connected in series with the holding contacts. Explain how this circurt operates.

The NC jog button provides a continuous path for current to flow which negates the start button

Refer to the circuit shown in Figure 10-4. The motor will not start or jog in the forward direction, but will start and jog normally in the reverse direction. Which of the following could cause this problem?

The coil of F starter is defective.

Refer to the circuit shown in Figure 10-7. Assume that when the start button is pressed the motor does not start, but when the inch push button is pressed the motor runs at reduced speed. Which of the following could NOT cause this problem?

The control transformer fuse is blown.

Using timers to sequence the operation of a machine is called __________.

Time-driven sequencing

What is the main purpose of jogging?

To bring a machine into position

One common method of unloading a compressor motor during startup is to use a control circuit with a timer relay.

True

What is the purpose of sequence control?

Forces the operator to follow a predetermined sequence

Which of the following is not a common timing mechanism used on timer relays?

Hydraulic timers

Referring to Figure 12-14, assume that the normally open 2M contact located between wire numbers 23 and 29 is welded closed. Also assume that none of the motors are running. What would happen if: a. The number 2 push button was to be pressed before the number 1 push button? b. The number 1 push button was to be pressed first?

4a. Motor 2 wouldn't be able to start since the 1m contact is still open 4b. Both would start at the same time

How are pneumatic timers adjusted?

Adjusting the needle valve (orifice opening with a valve) which adjusts the airflow

What are instantaneous contacts?

Contacts that change positions immediately when energized or de energized

Refer to the circuit shown in Figure 11-23. What is the function of resistor R4 in the circuit?

Current limiting resistor

Explain the operation of an on-delay relay.

Delay change when energized, immediately changes when de energized

Refer to the circuit shown in Figure 11-23. What is the function of diode D1 in the circuit?

Inductive kick protection

Explain the operation of an off-delay relay.

It delays the off

Explain the difference between inching and jogging.

Jogging is short jabs of power at full voltage, inching is short jabs of power at reduced voltage

What are the two basic classifications of timers?

On delay and off delay

Refer to the circuit shown in Figure 10-7. Assume that when the start push button is pressed the motor starts and runs normally. When the inch push button is pressed, the motor hums but does not start. Which of the following could cause the problem?

One of the resistors connected in series with the motor is open.

Assume that all three motors shown in Figure 12-14 are running. Now assume that the STOP button is pressed and motors #1 and #2 stop running, but motor #3 continues to operate. Which of the following could cause this problem?

The 2M contact between wire numbers 31 and 32 is hung closed.

Refer to the circuit shown in Figure 11-23. What is the function of resistor R3 in the circuit?

When the gate pulse is not there it shorts it to ground so the SCR turns off

Refer to the schematic diagram in Figure 12-14. Assume that the 1M contact located between wire numbers 29 and 30 had been connected normally closed instead of normally open. How would this circuit operate?

You can start motor 2 without motor 1 being started