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It is a great pleasure to announce the publication by McGraw-Hill of my new NEC 2011 guidebook. Reader feedback will be appreciated --



My second McGraw-Hill book for electricians, Troubleshooting and Repairing Commercial Electrical Equipment, now available from Amazon --






Now I've written a third McGraw-Hill book, out soon. The title is The Electricians's Trade Demystified. It is available for pre-order from Amazon. Click below --



You Can Pass Your Journeyman or Master Electrician's License Exam the First Time You Take It

Enroll in David Herres Electricians' Licensing Exam Course

(Details at electriciansexamprep.com )








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Wilderness Light Photography: Custom, commercial, landscape, nature, weddings, portraits, stock images by Judith Howcroft -- wildernesslightstockphotos.com


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Electricians' Books


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Milwaukee 49-22-4085 17 Piece Deluxe Electricians' Hole Saw Kit

Milwaukee 49-22-4085 17 Piece Deluxe Electricians' Hole Saw Kit

Milwaukee 49-22-4085 17 Piece Deluxe Electricians' Hole Saw Kit Since its founding in 1924, Milwaukee has focused on a single vision: to produce the best heavy-duty electric power tools and accessories available to professional user. Today, the Milwaukee name stands for the highest quality, durable and reliable professional tools money can buy. This deluxe 17 piece Electricians' Hole Saw Kit has the ultimate range of diameters available. The 12 diameters include: 5/8 inch, 3/4 inch, 7/8 inch, 1 inch, 1-1/8 inch, 1-1/4 inch, 1-3/8 inch, 1-1/2 inch, 1-3/4 inch, 2 inch, 2-1/2 inch, and 3 inch. The kit also includes arbor 49-56-7000 for hole saws up to 1-3/16 inch and arbor 49-56-7140 for hole saws 1-1/4 inch and larger. Additionally the kit has three pilot bits 49-56-8000 and an impact resistant plastic carrying case. The case is also sold separately as 48-55-0784. The hole saws in this kit are of the 6 teeth per inch design. Milwaukee 49-22-4085 17 Piece Deluxe Electricians' Hole Saw Kit Features: • Deluxe assortment of 12 hole saws, two arbors, and three pilot bits • Hole Saws: 5/8 in., 3/4 in., 7/8 in., 1 in., 1-1/8 in., 1-1/4 in., 1-3/8 in., 1-1/2 in., 1-3/4 in., 2 in., 2-1/2 in., 3 in.




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This article originally appeared in Electrical Business Magazine

PLCs -- An Overview



By David Herres



Allen Bradley's PanelView is an operator interface that accesses parameters, including diagnostics

Programmable logic controllers (PLCs) exist in great numbers in industrial settings throughout the world. In all but the smallest, simplest configurations, they greatly surpass mechanical relay-based equipment -- they are less expensive to install and operate, and more able to withstand variations in noise, vibrations and humidity levels. Workers love their user-friendly diagnostics and ease of operation.

These electrical devices are really highly specialized computers with central processing unit (CPU), memory and software. They are designed to control machines and industrial processes automatically and can generate reports that are used to ascertain production efficiency and incipient mechanical problems. Unlike PCs, they do not employ hard drives; instead they have internal rechargeable batteries that keep the contents of the microprocessor-based memory intact.

In today's industrial setting we see mostly the modular rack-based system. The rack accepts various input and output (I/O) modules that slide in and plug into place. There are separate slots for analogue and digital modules, depending upon the needs of in situ (in-place) sensors and actuators.

the power supply also plugs into the rack, and may be AC or DC. Electrical power must be highly filtered and regulated to provide the needed stability for the solid-state circuitry in the processing unit.

PLCs were developed in the 1960's in response to problems plaguing the automotive industry. Because car makers perceived (rightly or wrongly) that the public wanted totally new designs every 12 months, Detroit engineers periodically tore apart their machinery -- including control apparatus -- to retool for a new production cycle. Relay-based production control lacked flexibility and so the annual changeover was seen as necessary.

In 1968, General Motors took delivery of the world's first PLC and, at that point, the idea of virtual switches and relays emerged. These devices are no longer hardware elements, but instead exist as software instructions that reside within the microcircuitry of the central processing unit. Today, it is possible to program machine controllers by plugging in, let's say, a laptop computer and manipulating simple ladder schematics on on screen so that the machinery will perform in diverse ways as the need arises. There is unlimited flexibility and no waste.

Internal Mechanisms

A PLC consists of solid-state circuitry within an incredibly rugged housing. It has varying numbers of I/O modules and a CPU with a serial or other interface capable of communicating with a conventional personal computer or dedicated terminal.

Included with the PLC is a disc-based software enabling the technician to place virtual components within an onscreen ladder diagram and so quickly program the PLC. Programming in most instances is based on ladder circuitry. The left rail is the positive pole and the right rail is the ground bus. The program starts at the top. Each rung consists of an input and an output; in other words, one complete executed command. The input is on the left and the output is on the right. These elements each have a numerical address, such as 0500 or 1000. A simple example would be a single rung with a switch on the left and a light bulb on the right.

Equipment from various vendors incorporates somewhat different programming conventions. Most systems require and END command. When a PLC is operating, it is continuously scanning. The inputs are looked at first to see which ones are ON. Second, the PLC actually executes the program, starting at the top of the ladder and going down. Lastly, the PLC updates the output status, and is then ready for another scan. Depending on make and model, these scans take place in milliseconds.

A technician can place the PLC in either of two operating modes. In Programming mode, it receives instructions from a connected laptop. then the controller is switched over to Run mode where it is ready to control production.

PLCs range from small units with a limited number of inputs and outputs (these "bricks" cost as little as a couple of hundred dollars and fit in the palm of your hand) to elaborate models of immense functionality that require many floor to ceiling enclosures.

Depending on performance requirements, a varying number of input modules are inserted into the correct slots so that they are wired to the sensors, which may be some distance away depending on the size of the machine. Inputs may be voltage sensors, pressure transducers, limit switches, flow meters and thermocouples for temperature readings. they can be analogue or digital.

Similarly, output modules are placed in their slots, which are wired into low-current control circuits to motors and whatever actuators are needed to make the machinery run. They also may be digital or analog. An internal oscillator-based clock causes the PLC to scan the inputs at a high speed to read them. Then, based on the programming currently in place, the outputs are turned on in the right sequence with the correct time delays. Outputs can be latching or momentary, and the PLC is capable of highly nuanced commands.

Getting into PLC Work

Professionals wishing to enter this lucrative field need not be computer engineers, but rather accomplished electricians with good computer skills. The programming was originally conceived to be fairly intuitive for anyone who can read schematics so that it can be done in a factory setting with in-house personnel.

The initial phase is designing the project and specifying the correct equipment. For some applications, scan time is critical. it's desirable to start with excess I/O capacity since the machinery is likely to demand more functionality as time passes. Also, having spare slots in case of malfunction is a plus.

The best way to get started is to decide on a vendor and become familiar with that milieu. Manufacturers have extensive technical information online regarding basic theory, mechanical setup, programming procedures and operation. A lot of the technical information is free, but there are also moderately and high-priced courses. Meantime, some manufacturers -- such as Allen Bradley -- offer certification. Siemens has a broad range of courses ranging from free online material to machine-specific, onsite staffed presentations.

There are also some websites that offer free introductory tutorials and more expensive video-based courses with certification. Two good introductory sites are plcs.net and plcdev.com.
--END--


Books for electricians --

Here is a selection of the most significant electricians' books available online today, at the best prices around. Clicking on any logo provides access to reviews and ratings by electricians. A good place to start is with the 2008 NEC Handbook, which contains the complete text of the current code plus extensive commentary, diagrams and illustrations. Other books of interest for the electrician are available as well.

Low Voltage, Telecom, Fire Alarm Books --


HOME | Best Web Host | Question of the Week | Archived Questions | More Archived NEC Questions | Still More Archived Questions | Still More Archived Questions-2 | Still More Archived Questions-3 | Articles | Electrical Deficiencies | More Electrical Deficiencies | Electricians Tools | Online computers | Cybercorner | Electrician's License | Electronics Tutorials | Electricians' worksaving ideas | Electronic Theorems | Satellite Dish | Digital Cameras and Equipment | HTML Color Chart | Electronic Acronyms | Electronic Definitions | Electrician's Soldering Tutorial | Photovoltaic Power | Wind Power | Fire Alarm Basics | More Fire Alarm Info | Working with MC and EMT | Electricians' Color Code | Wiring Commercial Garages | Managing Your Emergency Lights | Lighting Design | Industrial Wiring | Wiring Ethernet | Residential Wiring | Low Voltage Wiring | PLC Overview | Electrical Troubleshooting Techniques | Using Loop Impedance Meter | Ten Common Grounding Errors |NEC and Low-Voltage Wiring | Raceway Protection and NEC | Working with Metal Raceway | Inductance and Characteristic Impedance | Understanding Capacitance | History of the Ethernet | Twisting Data Conductors | NEC Article 800, Communications Circuits | NEC Article 810, Radio and Television Equipment | NEC Article 820, Community Antenna and Radio Distribution Equipment | NEC Article 830, Network-Powered Broadband | Troubleshooting Submersible Well Pumps | Wiring Healthcare Facilities | First Edition National Electrical Code 1897 | Books for Electricians | Links


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