Characterization of the degree of a physical quantity for power speed
Power Power. The work done per unit time is called power, with P. If the work dA dt for time interval, the power is
Therefore, power is equal to the biasing force of the object the force point scalar product of velocity.
1. Overview
power is the object work done per unit time, i.e., the speed of power is a physical work. The higher the
rotational speed greater the power, the higher the maximum speed of the vehicle, the maximum power used to describe the car’s dynamic performance. The maximum power is generally used horsepower (PS) or kilowatts (kw), where 1 is equal to 0.735 kilowatts horsepower.
2, the power of the various titles
power is a physical quantity showing the speed of an object work, physics reactive power P = W / time t, is Watt w, we often in the media power saw units kw, ps, hp, bhp, whp the like, previously used in Italy as well as CV, where the edge is the SI unit kW kw, 1kw = 1000w, 1000 joules 1 second finish work, the power It is 1kw. Daily life, we often known as horsepower power unit is horses, just as the torque called torque.
In the car top, the greatest work machine is a power engine, the engine is the torque calculated, and the formula is quite simple: Power (w) = 2π × torque (Nm) × (rpm) speed / 60, to simplify the calculation becomes: power (kw) = torque (Nm) × speed (rpm) / 9549.
Depending on the metric and English, defined substantially not the same horsepower. Imperial horsepower (hp) is defined as: a horse in one minute to 200 lbs (LB) pulling heavy objects 165 feet (ft), after multiplication equals 33,000lb-ft/ Min; and metric horsepower (ps) was defined in a horse pulls a minute object 60 meters 75kg, after multiplication equals 4500kgm / min. After conversion unit, (1lb = 0.454kg; 1ft = 0.3048m) actually found 1hp = 4566kgm / min, and the metric 1ps = 4500kgm / min slightly different, but if the watt units (1w = 1Nm / sec = 9.8kgm / sec) to convert into, available 1hp = 746w; 1ps = 735w, two different results, a difference of about 1.5 weight percent.
The new standard EEC DIN Germany and the European Community have JIS in Japan is metric horsepower unit is ps, and SAE hp using imperial units, but due to the integration of the world economy and the advent of order avoid complicated conversion, more and more of the original data has been changed to provide undisputed international standards as per kw kw power output of the engine value.
3, power measurement technology and its applications
power measurement for measuring power consumption of electrical equipment, is widely used in household appliances, lighting equipment, industrial machinery and other research and development or production lines in. This article focuses on the method and its specific application of several power measurement.
L power measurement technique
Four different methods of measuring the power:
(1) a power law diode detector;
(2) is equivalent to the thermal power consumption assay;
(3) true RMS / DC (TRMS / DC) conversion power detection method;
(4) power logarithmic amplification detection method.
The following sections describe four methods are compared and their advantages and disadvantages.
1.1 power law detected by a diode
Figure l diode detector circuit the input power as shown in FIG. L (A) as a simple half-wave rectifier, a filter circuit, the overall circuit input resistance 50Ω. D is a rectifier, C is the filter capacitor. After RF input power PINRectifying and filtering the resulting output voltage U0. However, when the ambient temperature increases or decreases U0 vary significantly. FIG 1 (b) is detected via a diode circuit input power improved, which increases the temperature compensation circuit diode D2, and the rectified voltage of the diode D1 may be temperature compensated. A diode having a negative temperature coefficient, when the temperature rises the pressure drop decreases D1, D2, but also reduced the pressure drop, the final output voltage remains stable.
needs He noted that the diode detection circuit based on an average of the response, it does not directly measure the effective value of the input power, but is indirectly measured RMS RMS sine wave power based on the relationship with the average value. Obviously, when the measured waveform is not a sine wave, the crest factor is not equal to 1.4142, this time resulting in large measurement errors.
1.2 equivalent thermal power detection
Circuit
equivalent thermal power detection method is shown in Fig. It is equivalent to the heat of an unknown AC signal and a DC reference voltage effective heat compared. When the temperature difference signal resistor (R1) and the reference resistor (R2) is zero, power consumption of the two resistors are equal, thus the effective value of the unknown signal voltage equal to the DC reference voltage effective value. R1, R2 matching resistance, low temperature coefficient of resistance are used, the voltage drop are both KU1 and KU0. To measure temperature, in the vicinity of R1, R2, respectively, followed by further temperature sensor voltage output A, B, or may choose two thermocouples to measure temperature differences. R1 and R2 in a further series respectively overheat protection resistor.
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While the principles of the equivalent thermal power detection method is very simple, but difficult to achieve in practice, and the price is very expensive apparatus such detection.
1.3 True RMS / DC (TRMS / DC) conversion power detection method
True RMS / DC converter detects the maximum advantage of the power measurement method is independent of the signal waveform, which is “true RMS” means. Therefore, it can accurately measure the true RMS power arbitrary waveform. The first method is to measure the true RMS power using a monolithic true RMS / DC converter (e.g. type AD636), True RMS measured first voltage level, which is then converted into the true RMS power level.
Another block diagram of a true RMS power measurement circuit shown in Figure 3, a typical product of the circuit corresponding to AD8361 monolithic true RMS RF power detection system integrated circuit. A radio frequency signal input terminal U1, U0 is the DC voltage output terminal. US Termination 2.7 ~ 5.5V power supply, COM as public land. IREF is the reference operation mode select terminal, PWDN control terminal to the sleep mode. FLTR leading end of the filter, a capacitor is connected in parallel between the terminal end and the US, the filter cutoff frequency can be reduced. SREF control terminal for the reference power.
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from the input terminal U1 RMS RF voltage U1, through the flat sheet 1 generates a signal proportional to the ripple current U12 i, the mean square value of the current signal voltage is obtained by square-law detector U12 is constituted by the internal resistor R1 and capacitor C, is input to the inverting input terminal of the error amplifier. Using a squared error amplifier 2 may constitute a closed negative feedback circuit, the negative feedback signal to the inverting input terminal of the error amplifier temperature compensation. When the closed circuit reaches a steady state, the output voltage U0 (DC) power is proportional to the effective value of the input PIN. Have the relationship
Power 
This detection method has the following advantages: First, since the two are identical squarer, so when changing the scale does not affect the conversion accuracy; second,When the ambient temperature changes, the two squarer compensate each other so that the output voltage is held constant; third, squarer band used is very wide, from DC up to the microwave band.
1.4 pairs logarithmic amplification power detection method
The logarithmic amplifier detector is a multi-stage logarithmic amplifier configuration, the circuit block diagram shown in Figure 4. FIG 4 there are five logarithmic amplifier (A ~ E), each of the logarithmic amplifier gain is 20dB (i.e., the voltage amplification factor of lO-fold), the maximum output voltage is limited to lV. Thus, the slope of the logarithmic amplifier ks = lV / 20dB, namely 50mV / dB. Five pairs of logarithmic amplifier output voltages are supplied through detector summer (Σ), and then through a low pass filter to obtain an output voltage U0. Logarithmic amplifier capable of the envelope of the input AC signal logarithmic operation, the output voltage and kS, PIN in the relationship of
Power 
power
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where: b is the intercept, i.e., a value corresponding to the input power level when the output voltage is zero.
Common characteristic of the logarithmic amplifier to a sine wave input signal only. When the input signal is not a sine wave, the intercept on the characteristic curve will change, thus affecting the output voltage. At this point cope output readings to be amended. It is noted that, although the ADI produced AD8362 monolithic true RMS RF power detector also a logarithmic power detection method, but it is by using a unique patented technology can be applied to any input signal waveform, and intercept the characteristic curve It does not vary with the input signal.
Design of Monolithic DC power measurement system
MAX42ll belongs to low cost, low power consumption, high current power / current measurement system, which is precise using the current sense amplifier to measure the load current, to calculate the power reuse analog multiplier, so the load does not affect the ground path, and particularly suitable for power measurement of the battery current value of the power supply system. Detection and powerThe maximum error of the current are lower than ± 1.5%, a frequency bandwidth of 220kHz. Range of Si source voltage is measured 4-28v. Full-scale voltage when the detected current is 100mV or 150mV. Supply voltage range of Si is 2.7 ~ 5.5V, operating current of 670μA (typ). As shown in
A simplified circuit MAX42ll A / B / C in FIG. 5, including precision current detecting amplifier 25: 1 resistive divider, analog multiplier. The peripheral circuit includes a test voltage source 4 ~ 28V, 2. 7 ~ 5.5V operating voltage of the chip, a current detection resistor RSENSE and load. The measurement principle is to use the precision current sense amplifier to detect a load current, and the analog voltage proportional to the current, then the voltage applied to the analog multiplier, the load current and source voltage multiplied by the output from the load terminal POUT proportional to the power voltage. So that the power detection amplifier gain is G, the voltage across RSENSE is USENSE, RS + source voltage on the pin URS +, there are
Power
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inside the
MAX42l1A / B / C voltage divider resistors, to the analog multiplier and the RS + input. This design can accurately measure power source and the load to provide protection to the power supply (e.g. a battery). POUT from the end, the power signal and the current signal output terminal IOUT, respectively through A / D converter to the microcontroller. Ideally, the maximum load current detection voltage generated across the full range RSENSE. Select an appropriate gain, both of the current detection amplifier maximum output voltage, and saturation will not occur. In calculating the maximum value of RSENSE, RS + should be a differential voltage between the terminal end and the RS does not exceed the full-scale voltage detection. An appropriate resistance value is increased RSENSE can be improved USENSE, help to reduce the output error.
3 emitted monolithic true RMSPilot power measurement system
requirements of the communication system must ensure that the transmitting side is able to meet the power amplifier needs to be transmitted, and the output power does not exceed a predetermined index, otherwise it will cause overheating damage. Thus, in the transmitter circuit must be increased RF power measurement and the power control circuit. Similarly, measurement of RF power receiver is essential. Calculated according to the definition of RMS power is called “True RMS Power” (True Root Mean Square Power), referred to as “real power” (True Power). Since modern communication system having a constant load and source impedance (typically 50 [Omega), and therefore needs to know the power can be calculated RMS voltage, the power measurement can be converted to the effective value of the voltage measurement.
Traditional RF power meter circuit or radio frequency detection system complexity, low degree of integration. Recently, the United States launched ADI’s AD8361, AD8362 and AD8318 type fully integrated monolithic true RMS RF power measurement system, not only can accurately measure radio frequency (RF) power, can also measure the intermediate frequency (IF), low frequency (LF) power .
AD8318 is the use of the single-chip RF power measurement system SOI wafer hypervelocity combination of complementary bipolar fabrication process and high-speed SiGe made. Demodulating formula inside the logarithmic amplifier output voltage is proportional to the measured power, we can accurately measure the RF power of 1MHz ~ 8GHz. Measuring machine and adapted to wireless LAN base station radio output power. AD8318 not only far superior to the traditional products, and more cost-effective than the modular measurement system, a higher precision than the method using a diode power detector. AD8318 set accuracy, low noise, wide dynamic range and so on in a. AD8318 at input frequencies up to 5.8GHz, measurement accuracy better than ± ldB, the dynamic range is 55dB; at 8GHz accuracy of better than ± 3dB, the dynamic range over 58dB. And the output noise is only
Power
It logarithmic amplification detection power method, rating logarithmic slope of a 25mV / dB, and by changing the UOUT proportionality factor between the voltage feedback pin USET adjustment is performed. When the input signal from terminal IN +, a power level of an intercept 25dB. AD8318 typical application circuit 6 shown in FIG. 
Power
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AD8318 is designed to measure up to 8 GHz RF power designed, thus keeping iN +, and the functional units essential insulating circuit between a pin iN. UPSI the positive supply terminal of the AD8318, ups0 must meet the same voltage provided by the bias voltage input circuit UPSI end, the UOUT terminal end is a UPSO low noise output driver provides a bias voltage. There are some internal AD8318 independent public places. CMOP output driver is used as common ground. All public places should be connected to the printed low impedance pull the ground area. Allowed supply voltage range is 4.5 ~ 5.5V. C3 ~ C6 decoupling capacitors for the power, should be as close to the power and ground pins.
AD8318 AC-coupled, single-ended input. When the input signal frequency is lMHz ~ 8GHz, connected to the IN +, IN one end of the coupling capacitor (C1, C2) 0402 can be a surface lnF encapsulated ceramic capacitors, the coupling capacitor close to the IN +, IN- pin. External shunt resistor R1 (52.3Ω) cooperates with the IN + side, 50Ω impedance matching may be provided with a sufficient bandwidth. The AD8318 direct output voltage to a digital voltmeter (DVM), can also be delivered with A / D converter of the microcontroller (μC).
4, reference
1.http: //knology.chinaccm.com/phrase-2006030914330300190.html
2.http: //www.mcukf.com/article/dzjsjcyzz/2007/200711232949.html