ELECTRICAL CONTROL SYSTEMS 1 LEARNING … · learning activity packet electrical control systems 1 bb703-xb03uen timers and advanced systems

LEARNINGACTIVITYPACKET

ELECTRICAL CONTROL SYSTEMS 1

BB703-XB03UEN

TIMERS ANDADVANCED SYSTEMS

BB703-XB03UEN TIMERS AND ADVANCED SYSTEMSCopyright © 2012 Amatrol, Inc.

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LEARNING ACTIVITY PACKET 3

TIMERS AND ADVANCED SYSTEMS

INTRODUCTIONThis LAP covers the function and operation of time-delay relays and their

applications. The idea of using time as a control device is not new. Time-controlled devices are used every day at home, at school, and at work. In the morning, an alarm clock wakes you up at a predetermined time. At work, a time clock sounds a buzzer at lunch time. Time control is the most common method of sequencing the events in our lives.

This LAP also covers control circuits that can control multiple cylinders and can provide both automatic and manual modes of machine operation.

ITEMS NEEDEDAmatrol Supplied 1 90-EC1A Applied Electrical Control Learning System

School Supplied 1 Compressed Air Supply

FIRST EDITION, LAP 3, REV. AAmatrol, AMNET, CIMSOFT, MCL, MINI-CIM, IST, ITC, VEST, and Technovate are trademarks or registered trademarks of Amatrol, Inc. All other brand and product names are trademarks or registered trademarks of their respective companies.Copyright © 2012 by AMATROL, INC.All rights Reserved. No part of this publication may be reproduced, translated, or transmitted in any form or by any means, electronic, optical, mechanical, or magnetic, including but not limited to photographing, photocopying, recording or any information storage and retrieval system, without written permission of the copyright owner.Amatrol,Inc., 2400 Centennial Blvd., Jeffersonville, IN 47130 USA, Ph 812-288-8285, FAX 812-283-1584 www.amatrol.com


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TABLE OF CONTENTS

SEGMENT 1 TIME-DELAY RELAYS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4OBJECTIVE 1 Describe the function of a time-delay relay and give an applicationOBJECTIVE 2 Describe the operation of an on-delay timer relay and give its ladder diagram symbol

SKILL 1 Connect and operate a control circuit with a timer relaySKILL 2 Design a time-driven traffi c light circuit

OBJECTIVE 3 Describe the operation of an off-delay timer relay and give its schematic symbol

SEGMENT 2 TIME-DELAY RELAY APPLICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15OBJECTIVE 4 Describe the operation of a timer relay in an unloaded motor start circuit

SKILL 3 Connect and operate a control circuit to perform an unloaded start of a motorOBJECTIVE 5 Describe the operation of a timer relay in a cylinder dwell circuit

SKILL 4 Design a control circuit to perform a cylinder dwellOBJECTIVE 6 Describe the function of a time-delay relay in time-driven sequencing

SKILL 5 Design a control circuit to perform time-driven sequencing

SEGMENT 3 MULTIPLE CYLINDER CONTROL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24OBJECTIVE 7 Describe the function of multiple cylinders in a machineOBJECTIVE 8 Describe how multiple cylinders are controlled using one limit switch and give an application

SKILL 6 Design a dual-cylinder sequence circuit using one limit switchOBJECTIVE 9 Describe how multiple cylinders are controlled with multiple limit switches and give an application

SKILL 7 Connect and operate a dual-cylinder control circuit using two limit switchesSKILL 8 Design a continuous-cycle multiple-cylinder circuit

SEGMENT 4 MACHINE MODES OF OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35OBJECTIVE 10 Describe the function of manual and automatic modes in machine operation

SKILL 9 Connect and operate a circuit having both automatic and manual modes of operationOBJECTIVE 11 Describe two applications of manual controls

SKILL 10 Connect and operate a control circuit to simulate a two-pushbutton jog circuitOBJECTIVE 12 Describe fi ve basic guidelines to follow when working with manual control circuits

SKILL 11 Connect and operate a two-pushbutton jog circuit that will jog two cylinders independentlySKILL 12 Design a continuous-cycle, synchronized cylinder circuit with a manual mode


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SEGMENT 1TIME-DELAY RELAYS

OBJECTIVE 1 DESCRIBE THE FUNCTION OF A TIME-DELAY RELAY AND GIVE AN APPLICATION

Some industrial machines use time control to sequence the events of their operation. A typical device used to do this is a time-delay relay. The time-delay relay is a type of control relay that switches its contacts to a new state after a prede-termined time has elapsed.

A timer relay consists of three basic components:• Coil - When electrical current is applied, the coil will energize and cause the contacts to change states.• Contacts - A time-delay relay usually has one or more sets of N.O. and N.C. contacts.• Timing Mechanism - The timing mechanism is used to determine the desired time delay. Common timing mechanisms include pneumatic timers, solid-state timers, and motor driven timers.

A common application of time-delay or timer relay is on electric washers and dryers, like the ones in fi gure 1. Timers are used to sequence events in these machines.

Figure 1. Washer and Dryer with Timer Relay


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On a washer for example, a timer controls the wash cycle, the rinse cycle, and the spin cycle. On a dryer, a timer controls how long the tumbler motor will run and how long the heater element will be on.

OBJECTIVE 2 DESCRIBE THE OPERATION OF AN ON-DELAY TIMER RELAY AND GIVE ITS LADDER DIAGRAM SYMBOL

A time-delay relay is designed to operate in one of two basic operating modes:• On-delay • Off-delay

The operation of an on-delay timer relay is shown in fi gures 2 and 3. When the coil 1TR is de-energized, as shown in step 1, the timer relay contacts are in their normal states and the internal clock is reset to 0.

In step 2, the coil 1TR is energized. This causes the timer’s internal clock to run but the contacts remain in their normal states.

If the pushbutton is released before the timer times out, the coil will de-ener-gize and the timer of the relay will reset to 0.

Figure 2. On-Delay Timer Operation, Steps 1 and 2

1PB1TR

L1 L2

1

2

3

1TR A

1TR B

R

G

STEP 1: TIMER COIL OFF, TIMER RESET

1PB1TR

L2

1

2

3

1TR A

1TR B

R

G

STEP 2: COIL 1TR ENERGIZED, TIMER STARTS

1 3 2

1 4 2

1 5 2

1 3 2

1 4 2

1 5 2

TIMEDELAY

SETTING

TIMEDELAY

SETTING

TIMER COIL1TR

L1


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In step 3, as shown in fi gure 3, the timer’s internal clock has reached a preset time and the relay contacts energize.

The relay contacts will remain energized as long as coil 1TR is energized. When the coil is de-energized, the contacts will immediately return to their normal state and the clock resets to 0. This is shown in step 4.

Figure 3. On-Delay Timer Operation, Steps 3 and 4

Figure 4 shows the ladder diagram symbols for an on-delay relay. Timer relays sometimes also include a set of instantaneous contacts that energize when the coil energizes and de-energize when the coil de-energizes. These contacts work just like a standard relay.

Figure 4. Ladder Diagram Symbols for an On-Delay Timer Relay

1PB1TR

L1 L2

1

2

3

1TR A

1TR B

R

G

STEP 3: TIMER REACHES PRESET VALUECONTACTS ENERGIZE

1PB 1TRL1 L2

1

2

3

1TR A

1TR B

R

G

STEP 4: COIL 1TR DEENERGIZED, TIMER RESETSAND CONTACTS GO TO NORMAL STATES

1 3 2

1 4 2

1 5 2

1 3 2

1 4 2

1 5 2

TIMEDELAY

SETTING

TIMEDELAY

SETTING

1TR

COIL N.O. CONTACT1TR

N.C. CONTACT1TR

INSTANTANEOUSN.O. CONTACT

1TR

INSTANTANEOUSN.C. CONTACT

1TR

ON-DELAY RELAY


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SKILL 1 CONNECT AND OPERATE A CONTROL CIRCUIT WITH A TIMER RELAY

Procedure Overview

In this procedure, you will use a time-delay relay to control a logic circuit. You will use the normally closed contacts of the time-delay relay to turn off an indicator lamp after a given time that you will set has elapsed.

1. Perform the following substeps to set up the system.

A. Make sure the main power circuit breaker is off.

B. Remove any test leads on the front panel. 2. Connect the circuit shown in fi gure 5.

Figure 5. Pictorial and Ladder Diagram Using a Time-Delay Relay

NOTE

The time-delay relay on the 90-EC1A is an on-delay type relay that uses solid-state electronic components.

PICTORIAL DIAGRAM LADDER DIAGRAM

1

L1 L21PB

1TRB

2

1

1

3

5

2

2R

1TR

TOELECTRICAL

OUTLET


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Solid-state, time-delay relays use resistor-capacitor networks to perform the time delay function. The delay is accomplished due to a characteristic of resistor-capacitor networks called the RC time constant. The delay time is adjusted by changing the capacitance or resistance of the circuit. This change is accomplished by turning the timer knob to a desired time setting.

The cost of a solid-state timer relay is very low compared to other types of timer relays and they can easily be replaced. An example of a solid-state time delay relay is shown in fi gure 6.

Figure 6. Solid-State Timer Relay

3. Set the control knob to 5 seconds. 4. Turn on the main power circuit breaker. 5. Observe the red indicator lamp.

Red Lamp Status ______________________________________ (On/Off)

The lamp should be on at this time. The red indicator lamp will come on when the power circuit breaker is turned

on because the power source, L1, is wired to the normally closed contacts of the time-delay relay.

6. Perform the following substeps to operate the control circuit.

A. Press and hold 1PB and observe the red lamp.

Red Lamp Status ____________________________________ (On/Off)

You should observe that the lamp goes off 5 seconds after the coil is energized.

B. Release 1PB and observe the red lamp.


You should observe the red lamp come on. This indicates the timer’s contacts have reset to their normal states.

TIMER MODULE

TIME DELAYADJUSTMENT

KNOB

SUBBASE


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7. Set the timer control knob to zero. 8. Perform the following substeps to operate the circuit.

A. Press and hold 1PB and observe the red lamp.


The red indicator lamp will immediately go off because there is no delay time specifi ed. Therefore, the time-delay relay functions as a standard relay and the contacts shift without any delay when the coil is energized.

B. Release 1PB and observe the red lamp.


The indicator lamp will come on because the coil is de-energized and the contacts return to their normally closed position. This allows current to fl ow to the lamp.

9. Repeat step 7 using various settings on the timer control knob to test the operation of a time-delay relay.

10. Perform the following substeps to shut down the system.

A. Turn off the main power circuit breaker.

B. Remove the test leads.


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SKILL 2 DESIGN A TIME-DRIVEN TRAFFIC LIGHT CIRCUIT

Procedure Overview

In this procedure, you will design, connect, and operate a time-delay relay in a control circuit that will simulate a timed traffi c signal.

1. Design a control circuit that will simulate a traffi c signal with a pedestrian crosswalk. The circuit should be designed so that a pushbutton switch can be pressed to cause the traffi c light to immediately turn red and stay red for 20 seconds. This will allow the pedestrians time to safely cross the intersection. After 20 seconds, the light should change back to green.

Draw your circuit on a separate piece of paper. 2. Perform the following substeps to set up the system.

A. Make sure the main power circuit breaker is off.

B. Remove any test leads on the front panel. 3. Connect the circuit that you designed in step 1. 4. Set the control knob to the 20 second time delay. 5. Turn on the main power circuit breaker and observe the indicator lamps.


Green Lamp Status _____________________________________ (On/Off)

The green lamp should be on and the red lamp should be off indicating that the traffi c can fl ow through the intersection. A pedestrian cannot cross safely at this time.

6. Operate the circuit that you designed and connected. When the pushbutton is pressed, the green lamp should go off and the red

lamp should come on. This will last for 20 seconds. The lamps should then return to their previous status.

NOTE

In reality, when the pushbutton switch is activated, the traffi c light will not immediately change to red but will fi rst change to yellow for a few seconds to allow the traffi c time to stop.

7. Demonstrate the circuit to your instructor. This is part of your skills assessment.


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B. Remove the test leads. 9. Place a copy of your circuit design in your portfolio.

OBJECTIVE 3 DESCRIBE THE OPERATION OF AN OFF-DELAY TIMER RELAY AND GIVE ITS SCHEMATIC SYMBOL

The off-delay timer relay operates in a manner that is opposite of the on-delay timer just described. Figures 7 and 8 show the off-delay timer operation in steps.

In step 1, the timer relay contacts are de-energized when the coil 1TR is off. When the coil is energized, the contacts 1TRA and 1TRB immediately switch to their energized states, as shown in step 2. These contacts will remain energized as long as the coil is energized. The internal clock of the off-delay timer relay does not run while the coil is energized.

Figure 7. Off-Delay Timer Operation, Steps 1 and 2

1PB1TR

L1 L2

1

2

3

1TR A

1TR B

R

G

STEP 1: COIL 1TR OFF, TIMER CONTACTSARE IN THE NORMAL STATE

1PB1TR

L1 L2

1

2

3

1TR A

1TR B

R

G

STEP 2: COIL 1TR ENERGIZED, CONTACTS ENERGIZE,TIMER RESETS

1 3 2

1 4 2

1 5 2

1 3 2

1 4 2

1 5 2

TIMEDELAY

SETTING

TIMEDELAY

SETTING


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When the coil 1TR is de-energized by releasing 1PB, the internal clock starts running, as shown in step 3 of fi gure 8. However, the contacts remain energized.

When the internal clock reaches the preset time, the timer contacts then return to their normal states, as shown in step 4.

Figure 8. Off-Delay Timer Operation, Steps 3 and 4

1PB1TR

L1 L2

1

2

3

1TR A

1TR B

R

G

STEP 3: COIL 1TR DE ENERGIZED, CONTACTS STAYENERGIZED, TIMER STARTS RUNNING

1PB1TR

L1 L2

1

2

3

1TR A

1TR B

R

G

STEP 4: TIMER TIMES OUT, CONTACTS DE-ENERGIZE

1 3 2

1 4 2

1 5 2

1 3 2

1 4 2

1 5 2

TIMEDELAY

SETTING

TIMEDELAY

SETTING


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Figure 9 shows the ladder diagram symbols for an off-delay timer relay.

In this mode, when the relay coil is energized, the N.O. and N.C. contacts will immediately change states and will stay energized after the coil has de-energized until a predetermined time has elapsed.

Figure 9. Ladder Diagram Symbols for an Off-delay Timer Relay

1TR

COIL N.O. CONTACT1TR

N.C. CONTACT1TR


1TR


1TR

OFF-DELAY RELAY


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SEGMENT 1 SELF REVIEW

1. A(n) ___________ relay is a type of control relay that switches its contacts to a new state after a predetermined time has elapsed.

2. The three basic components of a time-delay relay are the coil, the contacts, and the __________ mechanism.

3. The symbol shown is a(n)_____________ on-delay relay contact.

4. The two basic operating modes for a time-delay relay are on-delay and _________.

5. An on-delay timer relay causes its contacts to change states __________ (before/after) the preset time has elapsed.

6. The symbol shown is a(n) __________ off-delay relay contact.


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SEGMENT 2TIME-DELAY RELAY APPLICATIONS

OBJECTIVE 4 DESCRIBE THE OPERATION OF A TIMER RELAY IN AN UNLOADED MOTOR START CIRCUIT

To produce high volumes of compressed air, centrifugal compressors are powered by large electric motors. Starting up a large electrical motor requires large amounts of electricity and produces more heat in the motor than when it is running at full load. To avoid overheating the motor and causing damage, it is recommended that the motor be unloaded when it is started.

One common method of unloading the compressor motor during startup is to use a control circuit with a timer relay. Figure 10 shows a typical centrifugal air compressor and its control panel.

Figure 10. Centrifugal Air Compressor

To begin operation, the operator presses the start button on the control panel. This starts the motor and signals the timer relay to begin its preset time delay. When the timer relay times out, the motor should be at normal operating speed. The relay then switches a valve’s position so that the air compressor can then begin to compress air.

ELAPSED TIMECLOCK

STARTP.B.

CONTROLPANELS


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SKILL 3 CONNECT AND OPERATE A CONTROL CIRCUIT TO PERFORM AN UNLOADED START OF A MOTOR

Procedure Overview

In this procedure, you will connect and operate a control circuit that uses a timer relay to simulate the unloaded start of a motor, such as is required on a centrifugal air compressor.

1. Set up the 90-EC1A. 2. Connect the circuit shown in fi gure 11. In this circuit, the red lamp represents the motor running in the unloaded

condition. The green lamp will represent the motor running in the loaded condition.

Figure 11. Ladder Diagram of a Control Circuit to Simulate an Unloaded Start a Compressor Motor

L1 L2

R

1CR

1TR

1PB

G1CRB

MOTOR RUNNING

MOTOR RUNNING

1TRB

UNLOADED

LOADED

1TRA

2PB

1CRA


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3. Set the control knob to 5 seconds. 4. Turn on the main power circuit breaker. 5. Press the 2PB momentarily and observe the red indicator lamp.


The red lamp should come on. This represents the motor starting up in the unloaded condition.

6. Observe the status of the two indicator lamps after the 5 second delay.



The red lamp should go off and the green light should come on. This indicates that the motor is at full speed and the compressor has started compressing air.

7. Press the stop pushbutton 1PB momentarily and observe the indicator lamps.



Both indicator lamps should now be off. This simulates turning off the motor. 8. Operate the circuit a few more times to get familiar with its operation. 9. Shut down the system.


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OBJECTIVE 5 DESCRIBE THE OPERATION OF A TIMER RELAY IN A CYLINDER DWELL CIRCUIT

During a machine’s sequence, it may be required to hold a cylinder in a certain position for some period of time before moving, or have a time delay between the operation of two cylinders. This process is called cylinder dwell. It is used in many machines including hydraulic presses and plastic injection molding machines.

For a plastic injection molding machine like the one in fi gure 12, hydraulic cylinders are used to open and close the two halves of the mold. A cylinder dwell is used to hold a cylinder in position before moving.

When the mold halves are pushed together or closed, hot melted plastic is injected into the mold. Before the mold can be pulled apart, a dwell period must occur to allow the plastic to cool and harden. This dwell period can be created by a timer relay.

Figure 12. Plastic Injection Molding Machine


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SKILL 4 DESIGN A CONTROL CIRCUIT TO PERFORM A CYLINDER DWELL

Procedure Overview

In this procedure, you will design a control circuit to perform a cylinder dwell using a time-delay relay.

1. Design a circuit to perform the following functions: • When the start pushbutton 1PB is pressed, the cylinder will extend and dwell for fi ve seconds.• After the fi ve seconds have elapsed, the cylinder will retract.

Draw your circuit design on a separate piece of paper. 2. Set up the 90-EC1A. 3. Connect the air supply to the system.

CAUTION

Do not exceed 100 psig/690 kpa when using this panel.

4. Connect the circuit that you designed in step 1. 5. Turn on the main power circuit breaker. 6. Perform the following substeps to operate the control circuit.

A. Set the timer control knob to 5 seconds.

B. Press 1PB and observe the cylinder.

Cylinder Status _____________________________ (Extends/Retracts)

The cylinder will extend fully. After 5 seconds, it will retract. 7. Repeat step 6 with different timer settings, observing the dwell time of the

cylinder each time. 8. Demonstrate the circuit to your instructor. This is part of your skills assessment. 9. Place a copy of your circuit design in your portfolio. 10. Shut down the system.


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OBJECTIVE 6 DESCRIBE THE FUNCTION OF A TIME-DELAY RELAY IN TIME-DRIVEN SEQUENCING

Instead of using limit switches to sequence the operation of a machine, timers are sometimes used. This is called time-driven sequencing.

For each distinct operation that takes place, a timer must be used. Each timer is wired into the control circuit so that its coil is energized when a particular step in the machine’s sequence is started.

For example, if a cylinder is the actuator being sequenced, the time delay is set for the precise amount of time required for the cylinder to extend or retract. When the timer times out and the cylinder has also completed its stroke, the timer energizes its contacts to cause a new step to take place.

A cylinder reciprocation circuit using a timer to sequence the operation is shown in fi gure 13. When 1PB is pressed, coil 1CR seals in and energizes solenoid A to extend the cylinder. Also timer relay coil 1TR is energized at the same time as solenoid A. When the timer times out, it opens contacts 1TRA. This de-energizes the seal-in circuit and causes the cylinder to retract.

Figure 13. Time-Driven Reciprocation Circuit

If the time delay is adjusted to time out exactly when the cylinder reaches the end of its stroke, the cylinder will operate in the same manner as if it were using a limit switch.

One of the problems with using a timer relay is that it often requires a number of timer adjustments before you get the desired delay time. Using limit switches to perform event driven sequencing is usually better.

L1 L2

11 2

2

31

4

START

1PB1TRA

1CR

4

1CRA

1CRB

2SOL-A

5

3

21TR


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SKILL 5 DESIGN A CONTROL CIRCUIT TO PERFORM TIME-DRIVEN SEQUENCING

Procedure Overview

In this procedure, you will design, connect and operate a circuit to perform time-driven sequencing on a cylinder.

1. Draw a ladder diagram for a time-driven sequence circuit that uses a timer relay instead of a limit switch to determine the desired full stroke of a cylinder.• When the circuit is not operating, the red indicator light should be on.• A pushbutton should be used to start the sequence.• When the circuit is activated, the green light should come on and the cylinder should extend until the timer times out. Once this occurs, the cylinder should retract.• The circuit should include a stop pushbutton.

Draw your circuit design on a separate piece of paper. 2. Set up the 90-EC1A. 3. Connect the air supply to the system. 4. Connect the circuit that you designed. 5. Turn on the main power circuit breaker. 6. Perform the following substeps to operate the control circuit.

A. Set the timer for about 1 second.

B. Press 2PB and observe the indicator lamps and the cylinder.


Green Lamp Status __________________________________ (On/Off)


Before 2PB is pressed, the red lamp should be on to indicate that the machine is not operating. When 2PB is pressed, the red lamp should go out and the green lamp should come on. This indicates that the cylinder has started to extend and the timer relay has started counting down.


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C. Observe the status of the cylinder when the timer times out.


It should start to retract because it has reached its full stroke as determined by the timer relay. The timer relay is serving the same purpose as a limit switch.

7. Adjust the timer up and down and repeat step 6. Observe how the different times affect the full stroke of the cylinder. 8. Demonstrate the circuit to your instructor. This is part of your skills

assessment. 9. Place a copy of your circuit design in your portfolio. 10. Shut down the system.


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1. An example of an unloaded start of a motor is on a centrifugal air __________.

2. A plastic injection mold is an example of an operation that uses a(n) __________ dwell.

3. _____________ sequencing uses timer relays in place of limit switches to sequence the operation of a machine.

4. For each distinct operation that takes place in a time-driven operation, a(n) ______ must be assigned.

5. Before the mold on a plastic injection molding machine is pulled apart, a(n) _____________ period must occur to allow the plastic to cool and harden.


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SEGMENT 3MULTIPLE CYLINDER CONTROL

OBJECTIVE 7 DESCRIBE THE FUNCTION OF MULTIPLE CYLINDERS IN A MACHINE

Many machines use multiple cylinders operating together to accomplish a task. One reason for this is one cylinder may not be able to provide enough force to move the load. Multiple cylinders working together can provide the needed extra force.

In order to work together, these cylinders must be synchronized.

Synchronizing cylinders means to make their rods move at the same time and speed. Two methods for synchronizing cylinders are:

• Mechanical - the cylinders can be attached to the same machine part to link them mechanically.• Flow control valves - the cylinders can have the fl ow to them balanced by fl ow control valves.

If multiple cylinders are synchronized, the control circuit used to control them differs according to the method used to synchronize them, as you will see.


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OBJECTIVE 8 DESCRIBE HOW MULTIPLE CYLINDERS ARE CONTROLLED USING ONE LIMIT SWITCH AND GIVE AN APPLICATION

Usually one limit switch is used for controlling multiple cylinders only when the cylinders are attached to the same machine part. This can be done because they will automatically extend and retract together. Therefore, the control circuit used for a single cylinder can be used to control multiple cylinders as well.

An example of using one limit switch to control multiple cylinders is the hydraulic press shown in fi gure 14. Both cylinders are attached to the platen, which extends to press the target material. The only limit switch needed in this case is one to sense when the cylinders are fully extended. The two cylinders working together allows more force to be applied, and the pressure is more evenly distributed.

Figure 14. Multiple Cylinder Sequencing Circuit Using One Limit Switch in Series

2-POSITIONVALVE

RP

1LS

CYLINDERCYLINDER

PLATEN


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SKILL 6 DESIGN A DUAL-CYLINDER SEQUENCE CIRCUIT USING ONE LIMIT SWITCH

Procedure Overview

In this procedure, you will design, connect, and operate a control switch to synchronize two cylinders using one limit switch.

1. Design a control circuit to perform the following functions:• Include both a start and stop pushbutton.• Use only one limit switch to sense when both cylinders are extended and will cause them to retract at the same time.• Use a different solenoid for each cylinder.• Assume that the cylinders are mechanically synchronized.

Draw your circuit on a separate piece of paper. 2. Set up the 90-EC1A. 3. Connect the air supply to the system. 4. Connect the circuit that you designed in step 1. 5. Turn on the main power circuit breaker and the air supply. 6. Perform the following substeps to operate the control circuit.

A. Press 2PB momentarily and observe the cylinders.

Cylinder 1 status ____________________________________________

Cylinder 2 status ____________________________________________

Both cylinders should extend at the same time until 2LS is actuated. Then, both cylinders should retract at the same time.

B. Press 2PB momentarily again. Before the cylinders are fully extended, press 1PB and observe the cylinders.

Cylinder 1 status ____________________________________________

Cylinder 2 status ____________________________________________

The cylinders should both extend until 1PB is pressed. At that point, the cylinders should retract.

7. Demonstrate your circuit to the instructor. This is part of your skill assessment. 8. Place a copy of your circuit design in your portfolio. 9. Repeat step 6 to get more familiar with the circuit’s operation. 10. Perform the following substeps to shut down the system.



C. Turn off the air supply.


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OBJECTIVE 9 DESCRIBE HOW MULTIPLE CYLINDERS ARE CONTROLLED WITH MULTIPLE LIMIT SWITCHES AND GIVE AN APPLICATION

In some applications, the cylinders are not attached to the same part of the machine. In these applications, fl ow control valves are often used to balance the speed of the cylinders.

Since the fl ow control valves are not very accurate, one limit switch will not be enough to sequence the cylinders. A separate limit switch will be needed for each cylinder to sense when each cylinder is extended.

For example, if you want to control two cylinders that are not attached to the same part, you will need to use two limit switches to accomplish your goal. One possible control circuit is shown in fi gure 15. This circuit uses limit switches connected in AND logic.

Figure 15. Multiple Cylinder Sequencing Circuit Using Two Limit Switches in Series

The N.O. limit switches (4LS and 2LS) connected in series create an AND logic circuit. When the start pushbutton 1PB on rung 1 is pressed, control relay 1CR is energized and sealed in. Contacts 1CRB on rung 3 now close and energize the solenoids to extend both cylinders.

The limit switches 2LS and 4LS will be actuated when both cylinders are fully extended. Now that the 2LS and 4LS contacts are closed, relay 2CR is energized and opens contacts 2CRA on rung 1. This causes the seal-in circuit for 1CR to drop out, causing the solenoids to de-energize and the cylinders to retract.

It does not matter if one cylinder fully extends before the other. Both limit switches must be actuated before the cylinders will retract.

1 43 21

2

L1 L2

1CRB6

32

SOL1

1CRA

2PB1CR

START

5

SOL

2-POSITION

VALVE

26

RP

STOP1PB

2LS 4LS

22CR

4

EXTENDED

7 84LS 2LS

2CRA

CYLINDER1/2

EXTEND


28

Another method of sequencing two cylinders using two limit switches is shown in fi gure 16. This circuit uses the two limit switches in a NAND logic circuit.

Figure 16. Multiple Cylinder Control Circuit Using Two Limit Switches in Parallel

This circuit does not require a second control relay to drop out the seal-in circuit. Both of the limit switches use the N.C. contacts to supply power to relay coil 1CR. When both limit switches are actuated, the N.C. contacts are opened and the power to 1CR is stopped. This causes the seal-in circuit to drop out which allows the cylinders to retract. Again, both limit switches must be actuated before the cylinders will retract.

An application of the two limit switch control method is a crimping machine for making a ladder. Crimping is the process of pressing an object into regular ridges or folds. Ladder crimping machines rely on two cylinders coming together at the same time (synchronized) to press the rungs of an aluminum ladder into the side rails, as shown in fi gure 17.

Figure 17. Aluminum Ladder with the Rungs Crimped

1 3 21

2

L1 L2

1CRB6

3 21-SOL

1

1CR5

STOP1PB

2

EXTEND

EXTEND

2LS

1LS4

2-SOL

1CRA

2PBSTART


29

In this case, the crimping process ensures that the rungs will not separate from the rails. Figure 18 shows the crimping process.

Figure 18. Crimping the Rungs on an Aluminum Ladder

Flow control valves are used to control the speed of the cylinders and help keep them synchronized. Keeping the cylinders synchronized is important so that they contact the ladder at the same time and their opposing force will keep the ladder in the center. Figure 19 shows a basic crimping machine setup.

Figure 19. Crimping Machine Fluid Power Pictorial

Neither of the cylinders can retract until both have fully extended. This ensures that the ladder rung is fully crimped on both sides.

CYLINDER #1 CYLINDER #2

RUNGS

SIDERAILS

RUNG BEFOREBEING CRIMPED

RUNG AFTERBEING CRIMPED

PRESSUREGAUGE

REGULATOR

1LS2LS 4LS

3LS

SOLENOIDOPERATED

DCV FLOWCONTROL

VALVE

FLOWCONTROL

VALVE

LIMITSWITCHES

CRIMPINGCYLINDER

CRIMPINGCYLINDER

MAIN LINE


30

SKILL 7 CONNECT AND OPERATE A DUAL-CYLINDER CONTROL CIRCUIT USING TWO LIMIT SWITCHES

Procedure Overview

In this procedure, you will connect and operate a control circuit that uses two limit switches connected in NAND logic to control two cylinders.

1. Set up the 90-EC1A. 2. Make sure the air supply is connected to the system. 3. Connect the circuit shown in fi gure 20.

Figure 20. Circuit Setup

4. Turn on the main power circuit breaker and the air supply. 5. Press 2PB momentarily and observe the operation of the cylinders.

Cylinder 1 status ______________________________ (Extends/Retracts)

Cylinder 2 status ______________________________ (Extends/Retracts)

Both cylinders should extend until both are fully extended, at which point, they should then retract.

1 3 21

2

L1 L2

1CRB6

3 21-SOL

1

1CR5

STOP1PB

2

CYLINDER 1

CYLINDER 2

4LS

2LS4

2-SOLEXTEND

EXTEND

1CRA

2PBSTART


31

6. Modify the circuit, as shown in fi gure 21, and set the time delay control to 1 second.

This will cause cylinder 2 to start to extend about 1 second after cylinder 1 starts to extend.

This will show how the two-limit-switch method causes the cylinders to retract at the same time, even if one is much slower.

Figure 21. Modifi ed Circuit

7. Now, press 2PB momentarily again and observe the cylinders.

Cylinder 1 status ______________________________________________

Cylinder 2 status ______________________________________________

Cylinder 1 will start to extend before cylinder 2. When the one second time delay times out, cylinder 2 will start to extend. Cylinder 1 will stay extended until cylinder 2 is fully extended and then they will both retract together.

NOTE

Because of the use of the two limit switches, it does not matter if the cylinders extend at the same speed. The cylinders will not be allowed to retract until both limit switches are actuated.





1 3 21

2

L1 L2

1CRB6

3 21-SOL

1

1 7

1CR5

STOP1PB

CYLINDER 1

CYLINDER 2

4LS

2LS4

2-SOL

EXTEND

EXTEND

1TR

1TRA

2

2

1CRA

2PBSTART


32

SKILL 8 DESIGN A CONTINUOUS-CYCLE MULTIPLE-CYLINDER CIRCUIT

Procedure Overview

In this procedure, you will design, connect, and operate a continuous-cycle circuit where the cylinders operate together.

1. Design a control circuit that will perform the following functions:• Include both a start and stop pushbutton.• Both cylinders should cycle together continuously.• Each cylinder should be controlled by a separate solenoid.• The circuit should be designed so that both cylinders will not extend until both are fully retracted, and will not retract until both are fully extended.

Draw your circuit design on a separate piece of paper.

HINT

You will have to use all four limit switches for this circuit.

2. Set up the 90-EC1A. 3. Make sure the air supply is connected to the system. 4. Connect the circuit that you designed in step 1. 5. Turn on the main power circuit breaker and the air supply. 6. Perform the following substeps to operate the control circuit.

A. Press 2PB and observe both cylinders.

Cylinder 1 status ____________________________________________

Cylinder 2 status ____________________________________________

Both should be continuously reciprocating.

B. Press 1PB and observe both cylinders.

Cylinder 1 status ____________________________________________

Cylinder 2 status ____________________________________________

Both should now retract and stop.

C. Press 2PB again and observe if the cylinders are synchronized.

Cylinders status _________________ (Synchronized/Not synchronized)

If they are synchronized, both extend limit switches must be energized before the cylinders will retract. Also, both retract limit switches must be energized before the cylinders can extend again.


33

7. Demonstrate the circuit to your instructor. This is part of your skill assessment. 8. Place a copy of your circuit design in your portfolio. 9. Perform the following substeps to shut down the system.





34


1. One reason why machines sometimes use multiple cylinders working together is to provide the extra ________ needed to move the load.

2. A(n) _________ is an application where cylinders are connected to the same machine part to synchronize their operation.

3. Using one _____ switch to control multiple cylinders is usually only used when the cylinders are attached to the same machine member.

4. If you have two cylinders to control, and they are not attached to the same machine member, you will need to use _______ limit switches.

5. An example of a machine that uses two limit switches to control two cylinders is a(n) ___________ machine.

6. Connecting two N.O. limit switches in series to control two cylinders is called _____ logic.

7. Controlling two cylinders using NAND logic requires connecting two N.C. limit switches in ___________.


35

SEGMENT 4MACHINE MODES OF OPERATION

OBJECTIVE 10 DESCRIBE THE FUNCTION OF MANUAL AND AUTOMATIC MODES IN MACHINE OPERATION

Most machines used in industry have two basic modes of operation, automatic and manual.

Automatic Mode

In the automatic mode, a machine will continuously cycle through its steps of operation after receiving a momentary input (start button). The machine will continue until it completes its task or receives a stop input.

The normal operating mode for most machines is the automatic mode. As long as a machine is in the automatic mode, it will continue to repeat whatever operation it is designed to do.

Figure 22 shows a typical automatic control circuit. It is a continuous-cycle cylinder reciprocation circuit.

Figure 22. Automatic Control Circuit

1 3 21

2

L1 L2

1CRB53 2

2CR1

1CRSTOP1PB 4

1-SOL

EXTEND

1LS 2LS6

2CRA

2CRB

7

8 2

4

5

1CRA

2PBSTART


36

Manual Mode

In the manual mode, machine parts are operated with manual inputs, usually pushbuttons.

Many machines that use automatic control systems offer a choice of operating the machine in either an automatic or manual mode. A selector switch is often used to allow the operator or technician to change from one mode of operation to the other.

Since it would be dangerous to try to adjust or repair a machine while it is in the automatic mode, the manual mode is most often used during machine setup and maintenance to make adjustments and to ensure proper operation. Manual mode applications will be discussed in more detail later in this LAP.


37

SKILL 9 CONNECT AND OPERATE A CIRCUIT HAVING BOTH AUTOMATIC AND MANUAL MODES OF OPERATION

Procedure Overview

In this procedure, you will connect and operate a control circuit that has an automatic mode and a manual mode of operation.


Figure 23. Control Circuit with Automatic and Manual Modes of Operation

If the circuit is in the automatic mode, the green indicator light will be on and the cylinder will extend and retract automatically.

When the manual mode is selected, the red indicator light will be on and the pushbutton 1PB can be used to manually extend (jog) the cylinder.

In this case, the mode of operation will be determined by the position of the selector switch.

4. Turn on the main power circuit breaker and the air supply.

1CRL1 L2

1

2

3

4

1PB

1LS 2LS

1CRA

1CRB

JOG FWD

1-SOL

1

1

2

2

4 5

6

8

RET'D EXT'D1SS

MAN AUTO

3

7

G

R2

2

5

6


38

5. Perform the following substeps to operate the control circuit in the automatic mode.

A. Place 1SS in the right-hand position and observe the cylinder and the green indicator lamp.

Cylinder status _________________________ (Cycles/Does not move)

Green Lamp status __________________________________ (On/Off)

The cylinder should be continuously cycling and the green lamp should be on. This will continue until 1SS is taken out of the automatic position.

In the automatic mode, the N.O. contacts of SS1 on rung 1 close and the N.C. contacts on rung 4 open. This locks the circuit into the auto-matic mode where the cylinder will reciprocate continuously. The manual controls will have no effect on the circuit at this time.

B. Place 1SS in the middle position and observe the cylinder and the indi-cator lamps.

Cylinder status _____________________________ (Extends/Retracts)


Red Lamp _________________________________________ (On/Off)

The cylinder should retract and both indicator lamps should be off. This is the OFF position.

6. Repeat step 5 to become more familiar with the automatic mode of operation. 7. Perform the following substeps to operate the circuit in the manual mode.

A. Place 1SS in the left-hand position and observe the cylinder and the lamps.


Red Lamp status ____________________________________ (On/Off)

The cylinder should be retracted and the red indicator lamp should be on. The green indicator should be off.

The set of N.O. contacts used for automatic operation on rung 1 are held open when the selector switch 1SS is placed in the manual position. At the same time, the set of N.C. contacts used for manual operation on rung 4 close. This provides a fl ow of electricity to 1PB, which is used to manu-ally control the cylinder. This manual control of the cylinder is known as jogging and will be discussed in more detail later in this LAP.


39

B. Press and hold 1PB and observe the cylinder.


The cylinder should now extend and stay fully extended until 1PB is released. This is the manual mode.

Pressing 1PB allows electricity to fl ow to the solenoid-operated direc-tional control valve, causing it to energize. This changes the direction of air fl ow so that the cylinder begins to extend.

C. Release 1PB and observe the cylinder.


The cylinder should now retract because the solenoid-operated DCV only has two positions. If it had three positions, the cylinder would have stayed where it was when 1PB was released.

8. Repeat step 7 to familiarize yourself with the manual mode of operation. 9. Perform the following substeps to shut down the system.





40

OBJECTIVE 11 DESCRIBE TWO APPLICATIONS OF MANUAL CONTROLS

There are two basic applications for manual controls on an automatic machine:• Malfunction• Machine Setup

Malfunction

If the machine fails while it is operating in the automatic mode, the machine can be switched to manual operation. This allows the operator to manually operate the machine and reset the position of the actuators. Also, in some cases, parts of the cycle may have to be performed manually before the machine can be reset.

Machine Setup

It may be necessary, in order to set up and adjust a machine, to make the machine move to certain positions or perform part of its cycle. This is usually done with the manual controls. As discussed earlier, the manual operation is called jogging. The pushbuttons used are called jog pushbuttons.

A single jog pushbutton can be used, as shown in fi gure 24, if the machine only has a single actuator that operates in one direction.

Figure 24. Single Job Pushbutton Circuit

1-SOL

FORWARD

L1

1CR

1CRA

JOG1PB

L2


41

If the actuator operates in two directions, two pushbuttons can also be used, one for forward jog and the other for reverse jog, as shown in fi gure 25. More jog pushbuttons may be needed if a machine has more than one cylinder.

Figure 25. Two-Pushbutton Job Control Circuit

In fi gure 25, if jog pushbutton 1PB is pressed, control relay 1CR is energized and the N.O. contacts on rung 3 close and activate the solenoid 1-SOL. This starts the forward jog of the cylinder. Similarly, if jog pushbutton 2PB is pressed, the cylinder will be jogged in reverse.

NOTE

In this confi guration, the pushbuttons should not be activated at the same time.

1 3 21

32

1-SOL

L1 L2

FORWARD

42

2-SOL

REVERSE

1

1CR

1 4 22

2CR

1CR5

12CR

6

JOG FWD1PB

JOG REV2PB


42

SKILL 10 CONNECT AND OPERATE A CONTROL CIRCUIT TO SIMULATE A TWO-PUSHBUTTON JOG CIRCUIT

Procedure Overview

In this procedure, you will connect and operate a circuit that will simulate the operation of a simple two-pushbutton jog circuit. The indicator lamps will be used to simulate the operation of a cylinder as it is jogged forward and in the reverse. The green lamp will indicate jog forward. The red lamp will indicate jog reverse.

1. Set up the 90-EC1A. 2. Connect the circuit shown in fi gure 26.

Figure 26. Two-Pushbutton Jog Control Circuit

1 3 21

32

L1 L2

FORWARD

42

REVERSE

1

1CR

1 4 22

2CR

1CR

5

12CR

6

JOG FWD1PB

JOG REV2PB

R

G


43

3. Turn on the main power circuit breaker. 4. Perform the following substeps to operate the circuit.

A. Press and hold 1PB and observe the indicator lamps.



The green lamp should be on because 1PB is the jog forward pushbutton. The red lamp should be off.

B. Release 1PB and observe the indicator lamps.



Both lamps should now be off indicating that the cylinder is holding the position it was in when the forward jog pushbutton was released.

C. Now, press and hold 2PB and observe the indicator lamps.



The red lamp should now be on, indicating that 2PB is the reverse jog pushbutton. The green lamp should be off.

D. Release 2PB. 5. Repeat step 4 to get familiar with the circuit’s operation. 6. Design a circuit to perform the following functions:

• Uses the 3-position selector switch on the 90-EC1A to perform the same operation as the two pushbuttons in fi gure 26.• The right-hand position of the switch will be jog forward.• The left-hand position will be jog reverse.• The center position of the switch should act like both pushbuttons are off.

Draw your circuit design on a separate piece of paper. 7. Connect and operate the circuit you designed in step 6. 8. Perform the following substeps to shut down the system.




44

OBJECTIVE 12 DESCRIBE FIVE BASIC GUIDELINES TO FOLLOW WHEN WORKING WITH MANUAL CONTROL CIRCUITS

Five basic guidelines to follow when working with manual control circuits are:

1. Control Relays - It is better to energize the solenoids through control relays, if possible, as shown in fi gure 27. It is allowable to energize sole-noids directly from the jog pushbutton if the duration is short. However, it is not usually recommended.

Figure 27. Jogging Cylinders through Control Relays

2. Slow Jog Speed - Jogging should normally be done at the slowest machine speed to provide maximum safety.

3. No Manual Overrides - It is not good practice to jog an actuator using the manual overrides on the valves. The operator may not be able to get a clear view of the total operation of the machine.

Also, this may cause solenoids of other valves to be energized and other actions to occur that may be dangerous to the operator.

4. Mode Lockout - When the machine is in one mode, the other mode should be locked out. This is usually done electrically with a selector switch. When the machine is in the manual mode, the automatic portion of the circuit should be completely locked out.

When the machine is in the automatic mode, the manual portion of the circuit should be completely locked out.

5. Jog Pushbuttons - Jogging is most often accomplished by using a push-button switch to energize each solenoid. A two-position selector switch can also be used to turn the jog function on and off.

1 3 21

32

1-SOL

L1 L2

FORWARD

42

2-SOL

REVERSE

1

1CR

1 4 22

2CR

1CR5

12CR

6

JOG FWD1PB

JOG REV2PB


45

SKILL 11 CONNECT AND OPERATE A TWO-PUSHBUTTON JOG CIRCUIT THAT WILL JOG TWO CYLINDERS INDEPENDENTLY

Procedure Overview

In this procedure, you will connect and operate a two-pushbutton jog circuit. 1PB will jog cylinder 1 and 2PB will jog cylinder 2. Try to observe as many of the guidelines for working with manual control circuits as possible.


NOTE

Notice that the solenoids are energized through the control relays 1CR and 2CR. This meets the requirements of guideline number 1.

Figure 28. Two-Pushbutton Jog Control Circuit to Jog Two Cylinders

4. Turn on the main power circuit breaker and the air supply.

1CRL1 L2

1PB

1LS 2LS

1CRA

1CRB

JOG1

JOG2

1-SOL

1

1

24 5

6

7

RET'D EXT'D1SS

MAN AUTO

3

8 2

2

2PB

2-SOL

2CR

22CRB

2CRA

3LS

10

94LS

CYLINDER 1

CYLINDER 2


46

5. Perform the following substeps to operate the circuit.

A. Place 1SS in the right-hand position and observe the cylinders.

Cylinder 1 status ________________________ (Cycles/Does not move)


Both cylinders should continuously cycle because the automatic mode is selected.

B. Place 1SS in the left-hand position and observe the cylinders.

Cylinder 1 status _______________________ (Extends/Does not move)


Neither cylinder will move until the jog pushbuttons are activated because the manual mode is now selected. This meets the requirements of guide-line number 5.

NOTE

The automatic mode is locked out because the N.O. contacts of the selector switch are open. This meets the requirements of guideline number 4.

C. Press and hold 1PB and observe the cylinders.

Cylinder 1 status ____________________________ (Extends/Retracts)


Cylinder 1 should extend and stay until 1PB is released because 1PB is the jog pushbutton for cylinder 1.

Cylinder 2 should not extend or retract because its jog pushbutton has not been activated.

D. Release 1PB and observe cylinder 1.

Cylinder 1 status _____________________________(Extends/Retracts)

Cylinder 1 will now retract and stay.

E. Press and hold 2PB and observe the cylinders.



Cylinder 1 should not extend or retract. Cylinder 2 should extend and stay until 2PB is released.

F. Release 2PB and observe cylinder 2.


Cylinder 2 should retract and stay.


47

NOTE

The manual overrides on the solenoid-operated DCV’s were not used to jog the cylinders. This meets the requirements of guideline number 3.

6. Repeat step 5 to get familiar with the circuit’s operation. 7. Perform the following substeps to shut down the system.




NOTE

Since there is no way to control the speed of the cylinders on the 90-EC1A, we were unable to observe guideline number 2.

SKILL 12 DESIGN A CONTINUOUS-CYCLE, SYNCHRONIZED CYLINDER CIRCUIT WITH A MANUAL MODE

Procedure Overview

In this procedure, you will design a control circuit that will perform a continuous-cycle, dual-cylinder synchronized operation, with automatic and manual modes.

1. Design a circuit that will perform the following functions:• The circuit should perform a continuous dual cylinder synchronized operation.• The circuit should have both an automatic and a manual mode.• In the automatic mode, the cylinders should be synchronized and cycle continuously.• When the manual mode is selected, the automatic circuit is locked out and each cylinder can be jogged individually by its own jog pushbutton.

Draw your circuit design on a separate piece of paper. 2. Set up the 90-EC1A. 3. Make sure the air supply is connected to the system. 4. Connect the circuit you designed in step 1. 5. Turn on the main power circuit breaker.


48

6. Perform the following substeps to operate the circuit.

A. Place the selector switch 1SS in the right-hand position and observe the cylinders.

Cylinder 1 status _________________________ (Cycling/Not Cycling)

Cylinder 2 status _________________________ (Cycling/Not Cycling)

Both cylinders should be cycling.

B. Notice if the cylinders are synchronized.

Cylinders status _________________ (Synchronized/Not synchronized)

They should be synchronized. Both cylinders should retract only when both limit switches are energized.

C. Place 1SS in the center position and observe the cylinders.

Cylinder 1 status ____________________ (Cycling/Retracts and stops)

Cylinder 2 status ____________________ (Cycling/Retracts and stops)

Both cylinders should retract and stop because the center position is the OFF position.

D. Place 1SS in the left-hand position and observe the cylinders.



Neither cylinder should be moving at this point because the manual mode is now selected.

E. Press and hold jog pushbutton 1PB and observe the cylinders.



Cylinder 1 should extend and stay until 1PB is released. Cylinder 2 should not move because its jog button was not pressed.

F. Release 1PB and then press and hold 2PB and observe the cylinders.



Cylinder 1 should now retract and cylinder 2 should extend and stay until 2PB is released.

G. Release 2PB and observe the cylinders.



Cylinder 1 should not be affected. Cylinder 2 should now retract.

H. Press and hold 1PB and 2PB at the same time and observe the cylinders.



Both cylinders should now extend and stay until the pushbuttons are released.


49

I. Release both pushbuttons and observe the cylinders.

Cylinder 1 status _______________________ (Stays extended/Retracts)

Cylinder 2 status _______________________ (Stays extended/Retracts)

Both cylinders should now retract. 7. Demonstrate the circuit to your instructor. This is part of your skill assessment. 8. Place a copy of your circuit design in your portfolio. 9. Perform the following substeps to shut down the system.





50


1. The normal operating mode for most machines is the _________ mode.

2. ________ mode is most often used in machine setup and maintenance.

3. A(n) __________ switch is most often used to determine the desired operating mode.

4. The manual control of a cylinder with a pushbutton is known as __________.

5. The two basic applications for manual controls on automatic machines is operator control of the machine and _________.

6. Pushbuttons used for jogging are called __________ pushbuttons.

7. There are __________ basic guidelines to follow when working with manual control circuits.

8. Guideline number 1 says that it is better to energize solenoids through _______________.

9. Guideline number 2 says that jogging should be done at the __________ machine speed in order to provide maximum safety.

10. Guideline number __________ says that when a machine is in the manual mode, the automatic mode must be completely locked out.

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