ALLEN BRADLEY 1747-L551 PLC Processor

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Selecting Your Hardware Components 2–27 Transistor Output Transient Pulses This section applies to the following SLC 500 fixed I/O processors and SLC 500 I/O modules that have transistor outputs. Fixed I/O Processors 1747-L20E 1747-L20G 1747-L20L 1747-L20N 1747-L30L 1747-L40E 1747-L40L4 1746-OB8 1746-OBP8 1746-OV8 1746-OB16 1746-OBP16 1746-OV16 1746-OVP16 1746-OB32 1746-OV32 I/O Modules For the SLC 500 products listed above, the maximum duration of the transient pulse occurs when minimum load is connected to the output. However, for most applications the energy of the transient pulse is not sufficient to energize the load. ! ATTENTION: A transient pulse occurs in transistor outputs when the external DC supply voltage is applied to the common output terminals (e.g., via the master control relay). The sudden application of voltage creates this transient pulse. (See the following graph.) This condition is inherent in transistor outputs and is common to solid state devices. A transient pulse can occur regardless of the processor having power or not. (On-State Load Current) Current Transient (I) Duration of Transient (T) Time Publication 1747-6.2
2–28 Selecting Your Hardware Components To reduce the possibility of inadvertent operation of devices connected to transistor outputs, adhere to the following guidelines: • Either ensure that any programmable device connected to the transistor output is programmed to ignore all output signals until after the transient pulse has ended, • or add an external resistor in parallel to the load to increase the on-state load current. The duration of the transient pulse is reduced when the on-state load current is increased. The duration of the transient pulse is proportional to the load impedance. This is illustrated in the following graph. 10 9 Time Duration of Transient (ms) 8 7 6 5 4 3 2 1 0 1 100 200 300 400 500 600 700 800 900 On-State Load Current (mA) 1000 Example Increasing the load current by 100 mA decreases the transient time from approximately 7 ms to less than 2.5 ms. To calculate the size of the resistor added in parallel to increase the current, use the following information: 24V = your applied voltage Need 100 mA of load current to reduce the transient to < 2.5 ms. (taken from graph above) R (Ohms) = V (Volts) I (Amps) Resistor value (Ohms) = Applied voltage (Volts) / Desired current (Amps) = 24 / 0.1 = 240 (Ohms) P (Watts) = I 2 (Amps) x R (Ohms) Actual Power (Watts) = (Desired Current) 2 x Resistor Value = (0.1) 2 x 240 = 2.4 (Watts) Resistor size = 2 x Actual power (Watts) = 4.8W ≅ 5W Use a resistor rated for 240 Ohms at 5 Watts to decrease the transient time from approximately 7 ms to less than 2.5 ms. Publication 1747-6.2
Page 1 and 2: Allen-Bradley SLC 500 Modular Hardw
Page 3 and 4: The information below summarizes th
Page 5 and 6: iv Table of Contents DH-485 Interfa
Page 7 and 8: vi Table of Contents Recommendation
Page 9 and 10: viii Table of Contents Connecting t
Page 11 and 12: x Table of Contents Calculating Hea
Page 13 and 14: P-2 Preface How to Use this Manual
Page 15 and 16: P-4 Preface Conventions Used in thi
Page 17 and 18: 1-2 Quick Start for Experienced Use
Page 25 and 26: 2-2 Selecting Your Hardware Compone
Page 33 and 34: 2-10 Selecting Your Hardware Compon
Page 49: 2-26 Selecting Your Hardware Compon
Page 53 and 54: 3-2 System Installation Recommendat
Page 61 and 62: 3-10 System Installation Recommenda
Page 63 and 64: 3-12 System Installation Recommenda
Page 65 and 66: 4-2 Mounting Your SLC 500 Control S
Page 71 and 72: 5-2 Identifying the Components of Y
Page 79 and 80: 5-10 Identifying the Components of
Page 87 and 88: 6-2 Installing Your Hardware Compon
Page 95 and 96: 6-10 Installing Your Hardware Compo
Page 97 and 98: 7-2 Wiring Your I/O Modules Contact
Page 99 and 100: 7-4 Wiring Your I/O Modules Prepari
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7-6 Wiring Your I/O Modules Feature
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7-8 Wiring Your I/O Modules Octal L
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7-10 Wiring Your I/O Modules Using
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This chapter describes how to start
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Starting Up Your Control System 8-3
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This chapter covers the following m
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Maintaining Your Control System 9-3
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In this chapter, you will learn abo
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Troubleshooting 10-3 Replacing Fuse
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Troubleshooting 10-5 If the LEDs in
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Troubleshooting 10-7 If the LEDs in
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Troubleshooting 10-9 Identifying SL
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Troubleshooting 10-11 Troubleshooti
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Troubleshooting 10-13 If the LEDs i
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Troubleshooting 10-17 Identifying S
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Troubleshooting 10-19 If the RS232
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Troubleshooting 10-21 Identifying P
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Troubleshooting 10-25 Returning the
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11-2 Replacement Parts Catalog Numb
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The information in this appendix wi
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Setting Up the DH-485 Network A-3 O
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Setting Up the DH-485 Network A-5 E
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Setting Up the DH-485 Network A-7 I
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Setting Up the DH-485 Network A-9 T
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Setting Up the DH-485 Network A-11
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This appendix provides an overview
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RS-232 Communication Interface B-3
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This appendix provides an overview
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Setting Up the DH+ Network C-3 Wiri
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This appendix provides a brief intr
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Control Networks D-3 DeviceNet Netw
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- Use this Table to Calculate the
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Power Supply Worksheet E-3 Hardware
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This appendix will assist you in ca
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Calculating Heat Dissipation for th
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This appendix: • describes SLC 5/
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Communicating with Devices on an Et
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You can find the following terms us
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Glossary GL-3 Initiator — A node
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Glossary GL-5 Signal Delay — For
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I-2 Index hardware features, 5-2, 6
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I-4 Index DH-485 Communication Inte
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I-6 Index keyswitch positions for t
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I-8 Index Publication 1747-6.2 Q Qu
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I-10 Index T testing inputs, 8-5 ou
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ALLEN BRADLEY 1747-L551 PLC Processor

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