Metric horsepower, its adjustment is completely artificial, take a value very close to British horsepower. Is it stipulated that 1 meter horsepower means to complete 75 kilograms of force in 1 second? The work of rice. Namely: 1 m horsepower =75 kg force? =735 watts per second.
Countries such as Britain and the United States use British horsepower. 1 inch horsepower is equal to 550 foot pounds per second, which is equal to 745.7 watts. /kloc-In the late 8th century, British physicist Watt (1 736-1819) defined horsepower as the work of lifting a weight of 1000 pounds by 33 feet in1minute, which is English horsepower.
1 British horsepower = 1.05438+039 m horsepower. There is no special letter for metric horsepower, and the value of 1 metric horsepower is different from that of 1 British horsepower. Horsepower has been abolished in China.
Power refers to the work done by an object in unit time, that is, power is a physical quantity that describes the speed of doing work. The workload is fixed, and the shorter the time, the greater the power value.
The formula for finding power is power = work/time.
The formula for finding the power is also P=W/t =UI=I? R=U？ /R
P stands for power, the unit is "Watt", the abbreviation is "Watt" and the symbol is "W". W stands for work, the unit is "Joule", which is called "coke" for short, and the symbol is "J". T stands for time, the unit is "seconds" and the symbol is "S". Because W=F(f force) *s(s displacement) (the definition of work), the formula for calculating power can also be derived as p = f v (the power calculated when v represents the average speed is the average power of the corresponding process, and the power calculated when v represents the instantaneous speed is the instantaneous power of the corresponding state).
The greater the power, the higher the speed and the higher the maximum speed of the car. Maximum power is often used to describe the dynamic performance of a car. The maximum power is generally expressed in horsepower (PS) or kilowatt (kw), and 1 horsepower is equal to 0.735 kW.
1w= 1J/s
Power calculation formula: P=W/t (average power) P=FV (instantaneous power)
[Edit this paragraph] Various power terms
Power is a physical quantity indicating the speed at which an object does work. In physics, power P = work W/ time T, and the unit is Watt W. We often see the units of power in the media, such as k W, ps, hp, bhp, whp mw, etc. , and cv used in Italy before. Kilowatt here is the international standard unit, and it is1kw =1000 w. In daily life, we often call horsepower [1], and the unit is horse, just like torque is called torsion.
On the top of the car, the largest working machine is the engine, and the power of the engine is calculated by torque, and the calculation formula is quite simple: power (w) = 2π× torque (Nm) × rotational speed (rpm)/60, which becomes: power (kw)= torque (Nm)× rotational speed (rpm)/9.549 after simplified calculation.
Because of the difference between English and metric systems, the definition of horsepower is basically different. British horsepower (hp) is defined as: a horse pulls an object weighing 200 pounds (lb) 165 feet (ft) in one minute, which is equal to 33,000 pounds-feet/minute after multiplication; Metric horsepower (ps) is defined as a horse pulling a 75 kg object for 60 meters in one minute, which is equal to 4500 kg/min after multiplication. After unit conversion, (1lb = 0.454kg; 1ft=0.3048m) is found to be 1hp=4566kgm/min, which is slightly different from the metric 1ps=4500kgm/min. But if the unit is watts (1w =1nm/sec = 9.8kgm)1PS = 735w, the difference between the two different results is about 1.5%.
DIN in Germany is the same as the new European standard EEC. Japanese JIS uses metric ps as horsepower unit, while SAE uses English hp as horsepower unit. However, due to the arrival of the global integrated economy, in order to avoid complicated conversion, more and more original factory data are changed to provide the undisputed international standard unit kw as the engine output power value.
[Edit this paragraph] Uniform dynamic motion
Constant velocity motion refers to the motion with constant power p.
Basic relationship (no resistance):
P=Fv
Then:
s^3=( 16pt^3)/(27m)
v^2=(2Pt)/m
a^2=P/(2mt)
Because the power of most machines or creatures is basically unchanged under natural conditions, uniform power movement has its practical significance.
[Edit this paragraph] Electric energy metering technology and its application (Figure)
Power measurement is used to measure the power consumed by electrical equipment, which is widely used in the research and development or production line of household appliances, lighting equipment and industrial machines. This paper mainly introduces several power measurement methods and their specific applications.
L power measurement technology
There are four ways to measure power:
(1) diode detection power method;
(2) Equivalent thermal power consumption detection method;
(3) TRMS/DC conversion detection power method;
(4) Logarithmic amplification detection power method.
The following four methods are introduced respectively and their advantages and disadvantages are compared.
1. 1 Method of detecting power by diode
The circuit of diode detecting input power is shown in Figure L. Figure l(a) is a simple half-wave rectifier and filter circuit with a total input resistance of 50 Ω. D is rectifier and c is filter capacitor. The RF input power pin is rectified and filtered to obtain the output voltage U0. However, when the ambient temperature increases or decreases, U0 will change significantly. Figure 1(b) is an improved circuit for diode detection of input power. A temperature compensation diode D2 is added to compensate the rectified voltage of diode D 1. Diodes have a negative temperature coefficient. When the temperature increases, the voltage drop of D 1 will decrease, but the voltage drop of D2 will also decrease, and the final output voltage will remain stable.
It should be pointed out that the diode detection circuit can not directly measure the effective value of input power in response to the average value, but indirectly measure the effective value power according to the relationship between the effective value of sine wave and the average value. Obviously, when the measured waveform is not sine wave, the crest factor is not equal to 1.4 142, which will lead to a large measurement error.
1.2 equivalent thermal power consumption detection method
The circuit of the equivalent thermal power consumption detection method is shown in Figure 2. It compares the equivalent heat of unknown AC signal with the effective heat of DC reference voltage. When the temperature difference between the signal resistor (R 1) and the reference resistor (R2) is zero, the power consumption of the two resistors is equal, so the effective value of the unknown signal voltage is equal to the effective value of the DC reference voltage. R 1 and R2 are matching resistors, both of which adopt low temperature coefficient resistors, and the voltage drop is KU 1 and KU0 respectively. In order to measure the temperature difference, the voltage output temperature sensors A and B are connected near R 1 and R2 respectively, or two thermocouples can be selected to measure the temperature difference. R 1 and R2 are also respectively connected in series with overheating protection resistors.
Although the principle of equivalent thermal power consumption detection method is very simple, it is difficult to realize in practical application, and the price of this detection equipment is very expensive.
1.3 TRMS/DC conversion detection power method
The biggest advantage of the true RMS /DC conversion detection power method is that the measurement result has nothing to do with the waveform of the measured signal, which is the meaning of "true RMS". Therefore, it can accurately measure the true root mean square power of any waveform. The first method to measure true rms power is to use a single chip true rms /DC converter (such as AD636). First, measure the true rms voltage level, and then convert it into the true rms power level.
Another circuit block diagram for measuring true RMS power is shown in Figure 3. The typical product corresponding to this circuit is the integrated circuit (AD836 1) of a single-chip RF true RMS power detection system. U 1 is the RF signal input terminal, and U0 is the DC voltage output terminal. US is terminated with 2.7 ~ 5.5v power supply, and COM is common ground. IREF is the selection terminal of reference working mode, and PWDN is the control terminal of sleep mode. FLTR is the output end of the filter. Connecting a capacitor in parallel between this end and the American end can reduce the cut-off frequency of the filter. SREF is the power reference control terminal.
The RF rms voltage input from the terminal U 1 is U 1, and the pulse current signal I proportional to U 1 2 is generated through the wave leveler1. The mean square voltage of the current signal is obtained by a square law detector consisting of an internal resistor R 1 and a capacitor C, and is input to the noninverting input terminal of the error amplifier. The squarer 2 and the error amplifier can form a closed negative feedback circuit, and the negative feedback signal is applied to the inverting input of the error amplifier for temperature compensation. When the closed-loop circuit reaches a steady state, the output voltage U0(DC) is proportional to the input rms power pin. relational expression
Where: k is the output voltage sensitivity of true rms /DC converter, and the k of AD836 1 is 7.5mv/DBM.
This detection method has the following advantages: first, because the two squarers are exactly the same, the conversion accuracy will not be affected when the range changes; Secondly, when the ambient temperature changes, the two squarers can compensate each other to keep the output voltage stable; Thirdly, the frequency band of the squarer used is very wide, from DC to microwave band.
1.4 logarithmic amplification detection power method
Logarithmic amplifier detector is composed of multistage logarithmic amplifiers, and its circuit block diagram is shown in Figure 4. In Figure 4, * * has five logarithmic amplifiers (A ~ E), each logarithmic amplifier has a gain of 20dB (that is, the voltage amplification factor is lo times), and the maximum output voltage is limited to lV. Therefore, the slope of logarithmic amplifier ks = LV/20 dB, that is, 50 MV/dB. The output voltages of the five logarithmic amplifiers are respectively sent to the adder () through the detector, and then the output voltage U0 is obtained through the low-pass filter. Logarithmic amplifier can perform logarithmic operation on the envelope of input AC signal, and the relationship between its output voltage and kS and PIN is as follows.
Where: b is the intercept, which corresponds to the input power level value when the output voltage is zero.
The characteristic curve of ordinary logarithmic amplifier is only suitable for sine wave input signal. When the input signal is not sine wave, the intercept on the characteristic curve will change, thus affecting the output voltage value. At this time, the output reading should be corrected. It should be pointed out that the AD8362 single-chip RF true rms power detector produced by ADI also belongs to logarithmic detection power method, but it adopts unique patented technology and can be applied to any input signal waveform, and the intercept on the characteristic curve does not change with the input signal.
Design of single-chip DC power measurement system
MAX42ll is a low-cost, low-power and high-end DC power/current measurement system. It uses a precise current detection amplifier to measure the load current, and then uses an analog multiplier to calculate the power, so it does not affect the grounding path of the load, and is especially suitable for measuring the power and current value of the battery power supply system. The maximum error of detecting power and current is less than 65438 0.5%, and the frequency band width is 220kHz. The standard value of the measured power supply voltage is 4-28V. The full-scale voltage when detecting the current is1100mv or 150mV. The power supply voltage is 2.7~5.5V, and the working current is 670μA (typical).
The simplified circuit of max 42 LLA/B/C is shown in Figure 5, which mainly includes a precision current sense amplifier, a 25: 1 resistor divider and an analog multiplier. The peripheral circuit includes the tested power supply voltage of 4~28V, and the chip working voltage of 2. 7 ~ 5.5V, current detection resistor RSENSE and load. Its measuring principle is to use a precise current detection amplifier to detect the load current to obtain an analog voltage proportional to the current, and then add the voltage to the analog multiplier. After multiplying the load current by the source voltage, a voltage proportional to the load power is output from the POUT terminal. Assuming that the gain of the power sense amplifier is G, the voltage on r sense is USENSE, and the source voltage of the RS+ pin is URS+, then
The voltage dividing resistor inside MAX42l 1A/B/C/B/C is connected to the RS+ terminal and the input terminal of the analog multiplier. This design can accurately measure the power of power supply load and provide protection for power supply (such as battery). The power signal and current signal output by the POUT terminal and the IOUT terminal can be sent to the single chip microcomputer through the A/D converter respectively. Ideally, the maximum load current produces a full-scale detection voltage on RSENSE. Choosing the appropriate gain can make the current-sensitive amplifier obtain the maximum output voltage under unsaturated condition. When calculating the maximum value of RSENSE, the differential voltage between RS+ terminal and RS terminal should not exceed the full-scale detection voltage. Appropriately increasing the resistance value of RSENSE can improve USENSE and help reduce the output error.
Design of Single Chip Real RMS RF Power Measurement System
The requirement of communication system is to ensure that the power amplifier at the transmitter can meet the transmission needs and the output power does not exceed the specified index, otherwise the equipment will be overheated and damaged. Therefore, it is necessary to add RF power measurement and power control circuits in the transmitter circuit. Similarly, RF power measurement is also very important to the receiver. The power calculated according to the definition of effective value is called "true root mean square power" or "true power" for short. Because modern communication system has a constant load and impedance source (usually 50 Ω), power can be calculated only by knowing the effective voltage, and the measurement of power can be converted into the measurement of effective voltage.
The traditional RF power meter or RF detection system has complex circuit and low integration. Recently, analog devices of the United States successively introduced the integrated monolithic RF true RMS power measurement systems of AD836 1, AD8362 and AD83 18, which can not only accurately measure RF power, but also measure intermediate frequency (IF) and low frequency (LF) power.
AD83 18 is a single-chip RF power measurement system, which adopts a high-speed silicon-germanium manufacturing process combining on-chip silicon and ultra-high-speed complementary bipolar. The output voltage of its internal demodulation logarithmic amplifier is proportional to the measured power, which can accurately measure the RF power of 1 MHz ~ 8 GHz. It is suitable for measuring the wireless output power of computers and wireless LAN base stations. AD83 18 is not only far superior to traditional products, but also has higher cost performance than modular measurement system and higher accuracy than diode power detection method. AD83 18 combines high precision, low noise and wide dynamic range. The measurement accuracy of AD83 18 is better than that of ldB, and its dynamic range is 55dB. At the input frequency up to 8GHz, its accuracy is better than 3 dB and its dynamic range is over 58dB. Output noise is only
It uses logarithmic amplification to detect power, and the rated logarithmic slope is 25mV/dB, which can be adjusted by changing the proportional coefficient of the feedback voltage between the UOUT and USET pins. When the signal is input from the IN+ terminal, the interception power level is 25dB. The typical application circuit of AD83 18 is shown in Figure 6.
AD83 18 is specially designed to measure RF power up to 8 GHz, so it is very important to keep the INsulation between pins IN+ and in and the circuits of functional units. The positive power supply pins UPSI and UPS0 of the AD83 18 must be connected to the same voltage, with the UPSI pin providing bias voltage for the input circuit and the UPSO pin providing bias voltage for the low-noise output driver of the UOUT pin. AD83 18 also has some independent public lands. CMOP is used as the common ground of the output driver. All common * * * grounding shall be connected to the low impedance printed circuit board grounding area. The allowable power supply voltage range is 4.5 ~ 5.5V..C3 ~ C6 are power supply decoupling capacitors, which should be as close as possible to the power supply pin and ground.
AD83 18 adopts AC coupling and single-ended input mode. When the input signal frequency is LMHz ~ 8 GHz, the coupling capacitor (C 1, C2) connected to IN+ and IN- terminals can be 0402 lnF surface-mounted ceramic chip capacitor, and the coupling capacitor should be close to IN+ and IN- pins. The external shunt resistor R1(52.3 Ω) can provide a 50 Ω matching impedance with sufficient bandwidth when matched with the IN+ pin. The output voltage of AD83 18 can be directly sent to a digital voltmeter (DVM) or a single chip microcomputer (μC) with an analog-to-digital converter.
4 conclusion
Four commonly used power measurement methods are introduced in detail, and the design schemes of DC power measurement system and RF power measurement system are given.
5. Electricity of common household appliances
Air conditioning 1500W
The microwave oven is about1000 w w.
Electric furnaces are generally larger than1000 w.
Electric water heaters are generally greater than1000 w w.
Vacuum cleaner 800W
Hair dryer 500W
Electric iron 500W
The washing machine is less than 500W W w.
200 watt TV
Computer 200W
Range hood 140W
Refrigerator 100W
Electric fan 100W
Flashlight 0.5W
Calculator 0.5 MW
Electronic watch 0.0 1mW