CrazyEngineers Forum - Electrical & Electronics Engineering |
| Posted: 21 Mar 2011 11:45 PM PDT Hi, I know the basic working of a CMOS invertor. what I don't understand is how it works in the forbidden region. I'll ask my doubt with help of an example. (W/L)p=5*(W/L)n Un=3Up(pronounce U=myu) Vthn=0.7v=|Vthp| Vdd=5v Suppose at present my invertor output is 0v. I give a input voltage of 2.7v. What will be the value to which my output will settle. Repeat the same question with input=0.8v(the difference it will create is that the pmos will be initially in the linear region now.) From what I understand, in any of the case , pmos will try to charge the capacitor to 5v while the nmos will try to discharge it to 0v. So, I believe that the output will be 0v if the resistance of nmos is less than that of pmos and the output will remain at 5v otherwise. But, the resistance of a mosfet is not constant but varies with the current. Also, voltage characterstics of a invertor shows that of intermediate values such as 2.7v, the output is not 0v or 5v , but actually lies somewhere in between. So, basically I am confused. Can anybody help? Thanx in advance!! |
| Posted: 21 Mar 2011 11:55 AM PDT i have read this topic about producing electricity from shoes by using piezo electric effect..i am very inquisitive to know how that happens?can any one explain me the principle and process please.. |
| Posted: 21 Mar 2011 08:10 AM PDT Pressure Measurement -A major concern in process control applications is the measurement of fluid pressure. The term fluid means a substance that can flow; hence, the term applies to both liquids and gases. Both will occupy the container in which they are placed. -The pressure is equal to the force applied to the walls divided by the area that is perpendicular to the force. For a liquid at rest, the pressure exerted by the fluid at any point is perpendicular to the boundary of the liquid. Pressure is defined as a force applied to, or distributed over, a surface area as:- P=F/A Gauge and Absolute Pressure -Absolute pressure is the pressure measured above total vacuum or zero absolute, where zero absolute represents a total lack of pressure. -Gauge pressure is the pressure measured above atmospheric or barometric pressure. It represents the positive difference between measured pressure and existing atmospheric pressure.  Pressure Gauges -Pressure gauges are used for local indication and are the most common type of pressure-measurement instrument used in process industries. Pressure gauges consist of a dial or indicator and a pressure element. A pressure element converts pressure into a mechanical motion. -Most mechanical pressure elements rely on the pressure that acts on a surface area inside the element to produce a force that causes a mechanical deflection. The common elements used are Bourdon tubes diaphragms and bellows elements. -The following figure shows one of the most common and least expensive pressure gauges used in the process industries. This pressure gauge uses a "C" type Bourdon tube. In this device, a section of tubing that is closed at one end is partially flattened and coiled. When a pressure is applied to the open end, the tube uncoils. This movement provides a displacement that is proportional to the applied pressure. The tube is mechanically linked to a pointer on a pressure dial to give a calibrated reading.  - A Diaphragm is another device that is commonly used to convert pressure into a physical movement. A diaphragm is a flexible membrane. When two are fastened together they form a container called a capsule. In pressure- measuring instruments, the diaphragms are normally metallic. Pressure applied inside the diaphragm capsule causes it to expand and produce motion along its axis. - A diaphragm acts like a spring and will extend or contract until a force is developed that balances the pressure difference force. The amount of movement depends on how much spring there is in the type of metal used. - To amplify the motion that a diaphragm capsule produces, several capsules are connected end to end, as shown in the following figure. You can use diaphragm- type pressure gauges to measure gauge, absolute, or differential pressure.  - The Bellows pressure element is very similar to a diaphragm-type gauge in that it converts a pressure into a physical displacement. The difference is that typically the movement in a bellows is much more of a straight-line expansion. A typical bellows-type pressure gauge is manufactured by forming many accordion-like pleats into a cylindrical tube -You can use the motion that the pressure input signal produces to position a pointer, recorder pen, or the wiper of a potentiometer.  |
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