Wednesday, 29 July 2015
Battery, defined in a narrow sense is itself generally stored chemical energy into electrical energy device, broadly defined as pre-stored energy from the device into external power available. So, like solar conversion without storage function only means not a battery. Other names have batteries, batteries, and Chinese have storage tanks and bottles intended effect.
Historical battery can be traced back two thousand years ago in ancient Iraq era. In the capital Baghdad found unglazed clay pots. It is a copper and iron battery.
Type of Batteries
Chemical batteries, electrochemical cell means by an oxidation-reduction reaction, the positive electrode, a negative electrode active material of chemical energy, into electrical energy for a class of devices. Common redox reaction with different oxidation and reduction reactions that are carried out separately, the oxidation of the negative electrode, the reduction in the positive electrode, and the electron gains and losses is carried out by an external circuit, thus forming a current.
Dry and liquid batteries distinguish battery is limited to that period of early development. The first battery of a glass container filled with an electrolyte and two electrodes. Later we introduced to paste electrolyte-based batteries, also known as dry batteries.
Disposable batteries (Primary Battery), commonly known as "disposable" cell, because after their power runs out, can not be recharged using only discarded. Common disposable batteries include:
Manganese battery - voltage of about 1.5V, the battery capacity is low, the battery can output low, almost alkaline manganese batteries are replaced, except after long-term storage is not leaking harmful corrosive liquids, so still in use in low electricity requires long-term use of devices simultaneously, such as clock, infrared remote control and so on.
Alkaline manganese battery - voltage of about 1.5V, battery capacity and output of the battery than the zinc-manganese batteries is high, but less than nickel-metal hydride battery, after long-term storage of hazardous leaking corrosive liquids.
Other disposable batteries include zinc batteries, zinc-air battery, zinc-mercury batteries, mercury batteries, battery and magnesium hydroxide, manganese batteries.
Rechargeable batteries, also known as the secondary battery (Secondary battery), batteries. Rechargeable battery according to different production materials and workmanship, the advantage can be reused many times after it is charged, they can be full charged and discharged more than two times or even up to 2500, the rechargeable battery output current (load force) than large part disposable batteries is high. Common types are:
Lead-acid battery - voltage of about 12V, low capacity, but can output more power, battery, often used in automobiles for starting the engine to use, or for uninterruptible power system (UPS), radios, communications machine.
Friday, 24 July 2015
Avalanche diode negative resistance is generated solid microwave devices using semiconductor structure carrier impact ionization and the transit time of two physical effects.
PN junction one-way conductivity, resistivity is small, a large reverse resistance.
When the reverse voltage is increased to a certain value, reverse current suddenly increases. It is the reverse electrical breakdown. It points avalanche and Zener breakdown.
Avalanche breakdown PN junction reverse voltage is increased to a value, like an avalanche multiplication of carriers, as far and fast increase.
Take advantage of this feature is to make the crystal diode avalanche diode
Major domestic manufacturers have Haiou light OTRON brand.
Avalanche breakdown in the electric field, the carrier energy increases constantly collide with atoms in the crystal, so that a covalent bond is formed in the electron excitation of free electron - hole pairs. New carriers generated by the collision and free electron - hole pairs, which is a multiplier effect. 1 Health 2,2 Alive 4, the same increase as the avalanche of carriers.
Zener breakdown is completely different, at high reverse voltage, there is a strong electric field PN junction, which can directly destroy covalently bound electrons will be separated to form an electron - hole pair formed a large reverse current. Zener breakdown electric field strength required great!
Only in impurity concentration particularly large PN junction to do the job.
It is in the applied voltage can produce high-frequency oscillation of transistors. High-frequency oscillations generated works: the use of avalanche breakdown of the crystal injected carriers, because the wafer carrier transit will take some time, so its current lags the voltage, It is often used in the field of microwave oscillation circuit.
Tuesday, 21 July 2015
Ampere, referred to security, is the International System of Units in the current strength of the unit, the symbol is A. at the same time it is also one of the seven basic units of the International System of Units . Ampere is the French mathematician and physicist Andre - Marie Ampere named, in honor of his contribution in terms of classical electromagnetism.
The actual situation, ampere is a unit of time cross-sectional measure the amount of charge through a conductor. Within one second by the cross section of 1 coulomb charge (6.241 × 1018 electrons in the charge), the current size of 1 amp
small current can be expressed in mA, microamps and other units.
1 Amp (A) = 1000 (mA)
1 milliamperes (mA) = 1000 microamps (μA)
Ampere force law of proof in a parallel existence of two straight power-attraction or repulsion between wires. This force is used to formally defined amps:
Vacuum, in two parallel infinitely long straight conductor cross-section can be ignored, and the distance of one meter. Through the same size, the same constant current direction in the two wires, when the wire is attractive per meter by 2 × 10-7 Newton, the two wires of the current of one ampere.
Ampere was originally defined as a centimeter - tenth - second current unit abampere - grams. Its size is so determined to ensure the international system of units derived from other units ampere value obtained is appropriate.
"International ampere" is an older unit of electric current, defined as the silver nitrate solution to precipitate the current 0.001118000 grams of silver per second. After a more accurate measure found that the current is 0.99985 A.
This unit Ampere and Watt balance and Ohm's law in the unit volts, ohms linked.
Monday, 20 July 2015
First, the human ear any subjective feelings are "absolutely" objective measurements may be used to represent data, otherwise all the knowledge of cognitive psychology and the psychology of perception on all the deceptive; please do not doubt, even religion and love so complex ideas can be objectively measured, under relatively sound sense of hearing is so simple! But we may not know how the existing capacity measure, or someone else had found and we did not know.
The second, but not a simple physical phenomenon "objective measurement data," mostly psychological phenomenon. This is why the measurement data clearly incorrect, but the listener can feel good to hear, because of the psychological feelings and physical stimulation is not a linear relationship.
To take a simple example: Please find a white paper, starting from the middle of a half will completely blacked out. ok, then you will say, external physical stimuli is not just black and white two properties, what else? It really wrong ...... physiological phenomenon of human vision, through the so-called ZERO CROSSING conversion, you'll find close to the middle boundary, white, more white, black and more black; this is certainly no humans there will be a normal physiological and psychological phenomenon.
Therefore, if we only care about the qualitative and quantitative external physical stimuli, will never forgive restricted to physical stimuli only black and white, do not know the human psychological phenomenon is real, "especially from black to white and black to white and then to special"; Just watch see "only physical stimulation from outside" view of human senses, it is not limited and lost a lot of rich message.
Many people see here say: Behold! Objective measurements useless ...... The more outrageous mistake. Because, objectively measured "absolutely" helpful; you then can not see how there is absolutely subjective, "especially from black to white and black to white and then to special" feeling in a black paper; this feeling, though not on the physical stimulation, but it is absolutely linked to a specific physical stimulus. So the first point I would emphasize: "All the subjective feeling" absolutely "objective measurement data can be used to represent" the only question is: even if we find the correct physical measurement data, how do we "explain" to get corresponding psychological feelings.
Because of the psychological feelings and physical stimulation is not a linear relationship, so for the "physical measurement data" "correct interpretation" even more important than the "right measure." Any physical data are not directly correspond to any sense of hearing, all we need to "correct interpretation"; and this explanation is necessary is an objective, because everyone should all have similar physiological and psychological phenomenon. So, at first glance subjective psychological feelings, still reflects a variety of objective material or social factors, it will never be cool enough to hear so simple.
Thirdly, I hereby personally think: with objective physical measurement is the "basic", is "starting from scratch", is "self-growth start." Even if I did not play a sound people listen to music, I listen to music when I found into a bottleneck and intend to re-start, what to do? Return to the starting point, increasing the "voice" of the objective of the physical message from the start; so he began to desperately play sound.
Friday, 10 July 2015
Cassegrain antenna is another commonly used in microwave communication antennas, which evolved from a parabola. Cassegrain antenna consists of three parts, namely the main reflector, sub-reflector and the radiation source. In which a rotating parabolic main reflector, sub-reflector surface of the rotational hyperboloid. Structurally, the focus of a hyperbolic paraboloid focus coincides hyperboloid focal axis coincides with the axis paraboloid focus, and the focus of the radiation source is located on another double curved, as shown below. It was a reflection of the electromagnetic radiation emitted subreflector carried out, the electromagnetic wave reflection to the main reflector, and then after the main reflector reflected plane wave beam obtain directions to achieve directional transmission. Cassegrain antenna works as follows.
When the radiator located hyperboloid of revolution real focal point F1, the rays emitted from F1 after the reflected rays hyperboloid, the equivalent of the virtual focus hyperboloid emitted directly out of the rays. So as long as the focus of the hyperboloid virtual focus coincides with the paraboloid, the sub-reflecting surface can be the main ray reflecting surface is parabolic reflector in a plane wave radiated.
Cassegrain antenna with respect to a parabolic antenna is concerned, it will feed the radiation pattern from the feedforward parabolic manner changed after the feeding mode, which makes the structure of the antenna is more compact, making it more convenient. Also Cassegrain antenna is equivalent to a parabolic antenna with a long focal length, and this can be a long focal length to the distance from the antenna from the focal point of each aperture is nearly constant, thus space radiation attenuation effect on the feeder to be smaller so Cassegrain antenna efficiency is higher than the standard parabolic antenna.
Monday, 6 July 2015
Directional antenna refers to the transmitting and receiving electromagnetic waves is particularly strong on one or a few specific direction, while transmitting and receiving electromagnetic waves is zero or a minimum of an antenna in the other direction. Directional transmitting antenna is intended to increase the effective radiated power utilization, increase confidentiality; the main purpose of the use of directional receiving antenna to increase signal strength is enhanced anti-jamming capability.
Directional antenna used to cover a long street, and has the following advantages:
1, has a large forward gain
2, the signal, when the cell behind the cell it would potentially interfere with this feature is useful to inhibit later.
Also worth mentioning is the directional antenna can improve indoor coverage within the micro-cellular coverage in some buildings.
Directional antenna in the horizontal direction in Fig showed a range of angles of radiation, which is usually referred to directional. Like with omnidirectional antenna, beam width is smaller, the greater the gain. Directional antenna in a communication system generally used in communication distance, small-coverage, high target density, high frequency utilization environment.
We may also like this to think about the relationship between omnidirectional antennas and directional antennas: All will transmit a signal to the antenna in all directions around, you can receive the signals, directional antenna like antenna mask after a bowl-shaped reflective surface, signals can only be transmitted to the front, towards the back of the signal is blocked by the reflective surface and is reflected to the front, reinforced front signal strength.
Saturday, 4 July 2015
Ohm meter (ohmmeter), also known as resistance table, is a specialized instrument for measuring electrical resistance. Electromechanical components impede the flow of current nature, called the resistance in ohms. Milliohm meter special measuring small resistance; and megohms meter, also known as Megaohmmeter, or high table, the special measure very great resistance.
Ohmmeter original design, with a small battery voltage is applied to the resistor, and, with a modified galvanometer (galvanometer) to measure the current flowing through the resistor. Galvanometer scale marked change in ohms. Due to the constant voltage applied to the battery to ensure that the current will be inversely proportional to the resistance. So, know the current, you can get resistance.
As shown right ohmmeter scale representation from zero to infinity. When in contact with the two probes, the resistance is zero; when separated, the resistance is infinite. The majority of the number of domains between the two numbers to a logarithmic scale mode of expression. So, assuming the battery of emf 6 \ volt \, \!, You want to set current 4 \ mA \, \!, The internal resistance must be adjusted to 1.5 \ k \ Omega \, \!. When two probe together, the total resistance is 1.5 \ k \ Omega \, \!, Current is 4 \ mA \, \!, Ohm meter display shows the resistance to needle 0 \ k \ Omega \, \! .
When displaying the needle in the middle of zero and infinity, the current is 2 \ mA \, \!. So, the total resistance is 3 \ k \ Omega \, \!, The measured resistance is 1.5 \ k \ Omega \, \!.
When displaying the needle in the middle between zero and 1.5 \ k \ Omega \, \! When current is 3 \ mA \, \!. So, the total resistance is 2 \ k \ Omega \, \!, The measured resistance is 500 \ \ Omega \, \!.
When the display needle 1.5 \ k \ Omega \, \! In the middle with the infinite, the current is 1 \ mA \, \!. So, the total resistance is 6 \ k \ Omega \, \!, The measured resistance is 4.5 \ k \ Omega \, \!.
This ohmmeter has an important drawback is that it requires a very stable battery voltage. After a period of use, the voltage will gradually decrease. This will make ohm meter lose accuracy. When in contact with the two probes, the display no longer needle will point 0 \ k \ Omega \, \!, And will point to the growing resistance.