Sensitivity refers to the degree of change in response of a method to the change of unit concentration or unit quantity of the substance to be measured. It can be described by the ratio of the instrument response or other indicators to the corresponding concentration or quantity of the substance to be measured.
Relative to the measured change of sensitivity indicatordisplacementSensitivity is a sign of measuring physical instruments, especially electrical instruments pay attention to the improvement of instrument sensitivity.The study of sensitivity can deepen the understanding of the structure and principle of the instrument.
staybalanceThere is a small inconspicuous slider on the pointer ofSensibilityThe weight is used to adjust the sensitivity of the balance.Sensing weightMove upward to improve the sensitivity of the balance;The sensitivity of the balance when the sensing weight moves downwardreduce。
The beam and pointer of the balance are a fixed shaftobject, the rotation axis is the central knife edge O.When the mass in the two pans of the balance is unequal, the beam will tilt at a certain angle θqualityThey are m1 and m2 respectively (m1>m2), the mass of the beam is M, andfocusThe balance arm length is L at the place where O is h from the pointer.
The above formula shows that when the mass difference between two plates (m1-m2) is constantconditionThe higher the ratio L/M, the smaller the h, the greater the θ.That is, the higher the sensitivity of the balance.
Generally speaking, the L/M value of the balance cannot be adjusted, and the height of the center of gravity h of the two beams can be changed by the position of the sensing weight: when the sensing weight moves upward, the center of gravity increases, and h decreases, and the sensitivity of the balance increases;Otherwise, the sensitivity decreases.
The higher the sensitivity of the balance, the better. As h decreases and the center of gravity rises, the stability of the balance becomes worse. At this time, the smaller the restoring moment of gravity, Mghsin θ, the stability becomesrange。Therefore, the balance should be designed at the same timesensitivityAndstability。
watt-hour meter
laboratoryfrequently-usedwatt-hour meterIt is magnetoelectric, and its structure is rotatablecoilInstalled inPermanent magnetIn the magnetic field ofelectric currentWhen the hairspring flows through the coil, due to the interaction of current and magnetic field, the coil deflects an angle to overcome the resistance torque of the hairspring. When the magnetic induction strength, coil area, coil turns and hairspring strength are fixed, the current is in direct proportion to the angle of coil deflection. We regard the current Ig when the pointer is fully biased as the sensitivity of the meter,Full bias currentThe smaller the sensitivity, the higher the full bias current of the meter is generally 10 μ A to several hundred mA.
If you want to measure weak current (10-6~10-10 A) or small voltage (10-3~10-6 V), you should improve the sensitivity of the meter, and use a high sensitivity instrument, namelySensitive galvanometer。
The structure of sensitive galvanometer includes three main parts, from which we can see the principle of improving sensitivity.
Magnetic field part: radial magnetic field generated by permanent magnet.
Deflection part: the coil can rotate in the magnetic field, and its upper and lower ends are made of metal wire（Zhang silk）Tighten the tension wire and use it as the current lead at both ends of the coil.Since the rotating shaft and bearing of the ordinary ammeter are replaced by the tension wire, the mechanical friction is avoided,GalvanometerThe sensitivity of can be improved a lot.
Reading part: small mirror M is fixed on the coil, which reflects the light from the light source onto the scale and forms acursorWhen the current passes through the coil, the small mirror M turns over θ with the coil, and the reflected light turns over 2 θ.The distance that the cursor moves on the ruler d=2 θ L, and l is the distance from the small mirror M to the ruler.Since the deflection angle θ of the coil is proportional to the current Ig, the distance d of cursor movement can measure the current Ig.Using the cursor as the "pointer" instead of the metal pointer of the ordinary electricity meter is equivalent to lengthening the pointerlength, further improving the sensitivity of the galvanometer.
Multipurpose meter
textbookThe lower left corner of the upper multimeter head is marked with "5000 Ω/V", which indicates the sensitivity of the meterIg × Rv=U, ∨ Rv/U=1/Ig, so according to 5000 Ω/V, the full bias current Ig=U/Rv=1/5000=200 (μ A) of the meter head can be known. The larger the Rv/U value is, the smaller the full bias current of the meter head is, and the more sensitive the meter is.Therefore, this value is called sensitivity in the instructions of general multi-purpose meters.
Ig=1000 μ A, Rg=1000 ΩammeterModifiedVoltageWhat is the sensitivity of the meter?Yes 1/Ig=1000 Ω/V
Oscilloscope
Turn the square waveSignal generatorThe output frequency is 1KHz and the amplitude is 0.5V square waveOscilloscopeIf the screen shows the trace length in the horizontal direction, not less than 7.8 grids in J2458 oscilloscope, not less than 6.3 grids in 325-2 oscilloscope, and not less than 5 grids in J2459 oscilloscope, the X axis sensitivity of the oscilloscope is qualified.Otherwise, find out the cause and replace the failed components.
amplifier
yesenlargeIn general, the sensitivity refers to reaching the rated outputpowerOr voltageVoltageSize, so it is also called input sensitivity;yesloudspeaker boxFor example, sensitivity refers to applying 1W input power to the speakerhornHow many decibels can be produced 1 meter aheadsound pressureValue.
Television
The sensitivity of the TV refers to theFluorescent screenWhen a good image is displayed, the minimum signal voltage value that needs to be input from the antenna end indicates the TV's ability to receive weak electromagnetic signals.The sensitivity is usually expressed in "microvolts" or "millivolts". The smaller the value, the stronger its ability to receive weak signals, that is, the higher the sensitivity of the television.High sensitivity TV, good viewing effect at long distance.
The sensitivity of a TV mainly depends on the TVImage channelPart (tuner and IFamplifierPart).If the gain of the channel part is high and the noise is low, the sensitivity of the TV is high.domestictransistorBlack and white TV sets generally have a sensitivity of about 100 μ V, integrated circuit black and white TV sets have a sensitivity of about 150 μ V, and crystal color TV sets have a sensitivity of about 200 μ V.
The simplest way to judge the sensitivity of a TV set is to usecontrastThe method is to use several TVs of the same model and specification at the same place to receive signals from the same TV station or test signals, and then shorten the antenna length (be careful not to change the direction of the antenna) or remove the antennabrightnessSet the knob to the appropriate position, and set the color saturation knob to the minimum position. Judge the sensitivity by observing the noise point of the fluorescent screen when there is no signal.Generally, jumping black and white noise points are many and thick, indicating high sensitivity;The noise point is thin and small, and the sensitivity is low.A TV set with many noise points will disappear immediately and present a clear image once a TV signal arrives.If there are still noise points in the image background after there is a signal, it indicates that the machineSignal-to-noise ratioPoor, poor relative sensitivity, and not ideal.
headset
Sensitivity In a common sense,headsetThe sensitivity ofloudnessIn the case of, the power input is required.Headphone sensitivityHigher requiredInput powerThe smaller the powerSound sourceThe higher the output sound is.aboutWalkmanFor portable devices such as mobile devices, sensitivity is a very important indicator.In general,Walkman headsetSensitivity ratioMonitor earphoneHigh, about 110db. Therefore, for walkman, the higher the value, the better.
Microphone
Sensitivity isMicrophoneThe ratio of output voltage to input sound pressure under unit sound pressure excitationCompanyIt is mV/Pa.In the circuitlevelThe sensitivity can also be expressed in decibels.Early decibels are mostly expressed in dBm and dBV units: 0dBm=1mW/Pa, that is, the 1mW power output brought to the 600 Ω load under the input sound pressure of 1Pa is defined as 0dB;0dBV=1V/μ bar, the 1V voltage output generated under the input sound pressure of 1 μ bar is defined as 0dB.The current decibel is expressed in dB μ: 0dB μ=0.775V/Pa, that is, the microphone 0.775V voltage output under the input sound pressure of 1Pa is defined as 0dB (so the level measurement after the microphone sound pressure voltage conversion is unified to the reference unit of 0dB μ=0.775V commonly used in the circuit).
Obviously, no matter how the sensitivity is expressed, we can convert it to dB μ, provided that the line input is unified to the unit of Pa.
For example, the sensitivity of the NEUMANN U89 microphone is 8mV/Pa, and the sensitivity can be obtained directly from 20lg [(0.008V/Pa) ÷ (0.775V/Pa)], which is about - 40dB μ.
For another example, the sensitivity of AKG C414 microphone is - 60dBV, and the output voltage X: 20lg [(X V/Pa) ÷ (10V/Pa)]=- 60 of - 60dBV under the sound pressure of 1Pa is calculated from 0dBV=1V/μ bar=10V/Pa, and X=0.01 (V) is obtained, that is, its sensitivity is 10mV/Pa.From the equation 20lg [(0.01V/Pa) ÷ (0.775V/Pa)], the sensitivity is about - 37dB μ.
Radiographic inspection
Sensitivity is evaluationRadiographyThe most important indicator of quality, which marks the ability to find defects in radiographic inspection.Sensitivity is divided into absolute sensitivity and relative sensitivity.Absolute sensitivity refers to the minimum along the ray penetration direction that can be found on the ray negativedefectDimensions.The relative sensitivity is the smallest that can be founddefectThe size is expressed as a percentage of the penetration weldment thickness.Because it is impossible to know the minimum value along the direction of ray penetration in advancedefectThe size, therefore, must be measured by the known size of the artificial "defect" - image quality indicator.
Clayey soil
The ratio of unconfined compressive strength of clayey soil in undisturbed state to unconfined compressive strength tested immediately after remolding.It represents a characteristic measure of the sensitivity of clay to disturbed remolding.
Camera chip
Sensitivity ischipIs one of the important parameters ofPhysicssignificance.One refers to the photoelectric conversion capability of optical devices, andResponse rateHas the same meaning.That is, the sensitivity of the chip refers to the output signal voltage (current) of unit exposure within a certain spectral range. The unit can be nA/Lux, V/W, V/Lux, V/lm.The other refers to the lowest sensing capacity of the deviceradiationPower (or illuminance), andDetection rateHas the same meaning.The unit can be expressed in watts (W) or lux (Lux).
Differentiation of sensitivity, precision and accuracy
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Sensitivity of the instrument：
Sensitivity refers to the ability of the instrument to measure the minimum measured value.The smaller the measured minimum, the higher the sensitivity of the instrument.For example, the sensitivity of the balance is smaller, even if the maximum mass required for the balance pointer to deflect from the balance position to one graduation of the dial is smaller.For another example, the number "20k Ω/V" on the dial of the multipurpose meter indicates the sensitivity.Its physical meaning is that when the voltage of 1V is applied at both ends of the meter, the total internal resistance Rv (the sum of the internal resistance of the meter head and the additional voltage) of the meter required by the full deflection of the pointer is 20k Ω.The higher the number, the higher the sensitivity.This is because U=IgRv, that is, Rv/U=1/Ig. Obviously, the larger the Rv/U, the smaller the full bias current Ig, that is, the smaller the minimum current that the meter can measure, the higher the sensitivity[1]。
The higher the sensitivity of the instrument, the better, because the higher the sensitivity, the worse the stability of the measurement, or even difficult to measure, that is, the poor accuracy.Therefore, on the premise of ensuring the accuracy of measurement, the sensitivity is not easy to be too high.Sensitivity is generally for scales and electrical instruments, but not for rulers, calipers and screw micrometers[1]。
Precision of instrument：
The precision of the instrument, also called precision, generally refers to the minimum division value of the instrument.For example, if the minimum division of the meter scale is 1mm, its precision is 1mm, and the minimum division of the mercury thermometer is 0.2 ℃, its precision is 0.2 ℃.The smaller the minimum division value of the instrument, the higher its accuracy and sensitivity.For example, a thermometer with a minimum division of 0.1 ℃ has higher sensitivity and precision than a thermometer with a minimum division of 0.2 ℃[1]。
In normal use, the accuracy of the instrument is high, which indicates that the accuracy of the instrument is the premise of a certain accuracy, and what kind of accuracy is required to adapt to it.This is why people often use precision to describe accuracy[1]。
However, the accuracy of the instrument does not fully reflect its accuracy.For example, the additional voltage inside a voltmeter of a certain specification deteriorates, reducing its actual accuracy, but maintaining its accuracy.There is a difference between visible precision and accuracy.General instruments have precision problems[1]。
Accuracy of instrument：
The accuracy of an instrument generally refers to the percentage value of the maximum relative error when measuring the full deviation of its pointer under specified conditions.The accuracy of an electricity meter is 2.5, which means that the relative error does not exceed 2.5% of the full deflection, that is, its absolute error=range × accuracy.For example, for a DC ammeter with a measuring range of 0.6A, its maximum absolute error=0.6A × 2.5%=0.015A[1]。
Obviously, when the same meter is measured with different ranges, its maximum absolute error will be different.Therefore, when using an electricity meter, there is a problem of selecting an appropriate range.Accuracy generally refers to electrical instruments, but not to other instruments[1]。
