Helical spring

A spring is defined as an elastic body, whose function is to distort when loaded and to recover its original shape when the load is removed.

Helical springs.

The helical springs are made up of a wire coiled in the form of a helix and are primarily intended for compressive or tensile loads. The cross-section of the wire from which the spring is made may be circular, square or rectangular. Helical compression springs have applications to resist applied compression forces or in the push mode, store energy to provide the "push". Different forms of compression springs are produced.

The helical springs are said to be closely coiled when the spring wire is coiled so close that the plane containing each turn is nearly at right angles to the axis of the helix and the wire is subjected to torsion. in other words, in a closely coiled helical spring, the helix angle is very small, it is usually less than 10 degree. The major stresses produced in helical springs are shear stresses due to twisting. The load applied is parallel to or along the axis of the spring. In open coiled helical springs, the spring wire is coiled in such a way that there is a gap between the two consecutive turns, as a result of which the helix angle is large. Terms used ¡n Compression Springs The following terms used in connection with compression springs Solid length (Ls). When the compression spring is compressed until the coils come in contact with each other, then the spring is said to be solid. The solid length of a spring is the product of total number of coils and the diameter of the wire. Free length (Lo). The free length of a compression spring is the length of the spring in the free or unloaded condition. Load(P) The force applied to a spring that causes a deflection. Deflection Motion of spring ends or legs under the application or removal of an external load (P). Wire Diameter (d) - The diameter of the wire that is wound into a helix. Spring Index (C) - The ratio of mean coil diameter to wire diameter. A low index indicates a tightly wound spring (a relatively large wire size wound around a relatively small diameter mandrel giving a high rate). Coil Diameter (D) - The mean diameter of the helix, i.e., (D outer + Dinner)/2. Active Coils (Na) - The number of coils which actually deform when the spring is loaded, as opposed to the inactive turns at each end which are in contact with the spring seat or base. Total Coils (Nt)- The number of coils or turns in the spring. Pitch (p) - The distance from center to center of the wire in adjacent active coils Pitch Angle (a) - The angle between the coils and the base of the spring. The pitch angle is calculated from the equation Compression Spring Rate: The change in load per unit of deflection, generally expressed in pounds per inch. Spring rate is determined by the amount of force, in pounds, required to constrict a spring by one inch.

Windows 7

Windows 7 is Microsoft’s latest version of its Windows operating system. Unlike its predecessor, Vista, Windows 7 offers incremental upgrades and is aimed at ensuring maximum compatibility with applications and hardware already supported in windows Vista.

System Requirements

If you are currently running Windows Vista, then you can easily install Windows 7. Tests performed by various parties have consistently confirmed that Windows 7 outperformed Windows Vista on a similar hardware configuration. If you are coming from previous versions of Windows (pre-Vista), take note of the following suggested hardware requirements:

• 1 GHz or faster 32-bit or 64-bit processor

• 1 GB RAM (for 32-bit) or 2 GB RAM (for 64-bit)

• 16 GB of available disk space (for 32-bit) or 20 GB of available disk space (for 64 bit)

• DirectX 9 graphics device with Windows Display Driver Model 1.0 or higher (for Aero. Aero is the graphical user interface and default theme in most editions of Windows 7)

Commonly available editions of windows 7

1) Home Basic

This edition is designated for emerging markets only; it is for customers who are looking for an inexpensive entry-level Windows experience (limited Aero support, no features such as Windows Media Center or multitouch support).

2) Home Premium

This edition is designed for home users and will include features like Media Center, multitouch support, the Aero Glass UI, and so on.

3) Professional

This edition is designed for home workers and small businesses, and will include features like advanced network backup and the Encrypting File System.

4) Enterprise

Includes everything that Professional includes and adds BitLocker protection. It will have the option to encrypt USB flash drives and external hard disks. It also includes DirectAccess, which allows remote workers to access a company network securely without using a VPN, and federated search.

5) Ultimate

Includes all the features available in Windows 7.

Installing Windows 7

It is straightforward—if you’re doing a clean install, simply boot up your computer with the Windows 7 installation DVD inside the DVD drive and instruct your computer to boot from the DVD (you may need to press a key, such as F11 or F12, while the computer is starting to enter the boot selection screen).

While installing you will have a choice between upgrading your existing Windows or installing a fresh copy of Windows. Installing a fresh copy of Windows is recommended.

Windows 7 32 or 64-bit?

When deciding to move up to a 64- bit operating system, you should first consider what 64- bit gets you. Knowing what software runs on 64- bit should influence your decision; you will see no advantage if you are running 32-bit software on a 64- bit OS. You also lose the ability to run 16- bit software

More bits gets you access to more memory; the processor inside your PC communicates with your system memory (RAM) with numeric addressing. Thus, the maximum amount of memory a 32-bit processor can address is 4
gigabytes. Newer 64-bit processors can address 17,179,869,184 gigabytes (16 exabytes) of RAM.

During installing

Select this for 32 bit computer (32-bit (x86) architecture)

Select this for 64 bit computer (64-bit (x64) architecture)

Some of features of windows 7

Taskbar

The taskbar is now more than just a windows-switcher—it is also an application launcher.

Libraries

The Libraries is a new feature in Windows 7. Using the Libraries, you can group your files and folders into logical units so they are easier to manage.

Desktop Gadgets

Gadgets in Windows 7 now have a new lease on life. In Windows Vista, gadgets were constrained to the Sidebar, which was never really a popular feature among people with small-screen computers (netbooks and small portable computers). In Windows 7, gadgets are free to roam about on your desktop

Introduction to digital circuits

Engineers generally classify electronic circuits as being either analog or digital in nature.

Whether or not a device is digital depends upon

1. Does it have an alphanumeric (shows letters and numbers) display?
2. Does it have a memory or can it store information?
3. Can the device the programmed?

If the answer to any one of the three questions is yes, then the product probably contains digital circuitry.

Advantages of digital over analog circuits
1. Generally, digital circuits are easier to design using modem integrated circuits (ICs).
2. Information storage is easy to implement with digital.
3. Devices can be made programmable with digital.
4. More accuracy and precision is possible.
5. Digital circuitry is less affected by unwanted electrical interference called noise.

A signal can be defined as useful information transmitted within, to, or from electronics circuits. Signals are commonly represented as a voltage varying with time. However, a signal could be an electrical current that either vanes continuously (analog) or has an on-off characteristic (digital). An analog device is one that has a signal which varies continuously in step with the input. A digital device operates with a digital signal. The digital signal is only at +5 V or at 0 V. The HIGH voltage is ±5 V or commonly called logical 1; the LOW voltage is 0 V or commonly called logical 0. Circuits that handle only HIGH and LOW signals are called digital circuits. An analog signal assumes a continuous range of values: A digital signal assumes discrete (isolated, separate) values as there are two permitted values

Digital signals are composed of two well- defined voltage levels. Most of the voltage levels used in this class will be about +3 V to +5 V for HIGH and near 0 V (GND) for LOW. These are commonly called TTL voltage levels because they are used with the transistor- transistor logic family of ICs. Logic levels are different for various digital logic families, such as TTL and CMOS. These logic levels are commonly referred to as HIGH. LOW, and undefined.

Limitations of digital circuits

1. Most ‘real-world” events are analog in nature.
2. Analog processing is usually simpler and faster.

Digital circuits are appearing in more and more products primarily because of low-cost, reliable digital lCs. Other reasons for their growing popularity are accuracy, added stability, computer compatibility, memory, ease of use, simplicity of design and compatibility with alphanumeri displays.

Example of digital and analog device

A multimeter can measure continuity, resistance, voltage and sometimes even current, capacitance, temperature. The standard volt-ohm-millimeter (VOM) is an example of an analog measuring device. As the voltage, resistance, or current being measured by the VOM increases, the needle gradually and continuously moves up the scale. A digital multimeter (DMM) is an example of a digital measuring device. As the current, resistance, or voltage being measured by the DMM increases, the display jumps upward in small steps. The DMM is an example of digital circuitry taking over tasks previously performed only by analog devices. This turn toward digital circuitry is growing.