Method and circuit for eliminating systematic error in simple-pendulum period measurement

Abstract

The invention provides a method and circuit for eliminating a systematic error in simple-pendulum period measurement, so that a strict requirement that a sensor must be placed at a simple-pendulum balancing position in the prior art is eliminated and a systematic error caused by a sensor placing position offset in the prior art is eliminate completely. According to the invention, the placing position of the sensor is mot limited; and accurate measurement of the simple-pendulum period can be realized by placing the sensor at any place except the simple-pendulum vibration end point. Because theactual period, instead of the half period, of the simple pendulum is measured, conversion from the half period to the actual period is not needed; the operational amplifier, the voltage comparator andthe A / D converter in the prior art are removed and thus no pulse shaping circuit needs to be set separately; in the circuit, the switching circuit is formed by CMOS circuits, so that the circuit structure becomes simple, the anti-interference ability is enhanced, and the power consumption of the circuit is reduced.

Description

technical field [0001] The invention relates to a method and a measuring device for period accurate measurement of periodic reciprocating motion, in particular to a method and a measuring device for eliminating an instrument system error in the period measurement of a single pendulum for the experiment of measuring the acceleration of gravity with a single pendulum. Background technique [0002] The systematic error refers to the difference between the average result of the same large number of repeated measurements and the true value of the measurement. Generally speaking, the imperfection of the measurement steps will cause errors in the measurement results, some of which come from systematic errors and some from random errors. Random errors are assumed to arise from unpredictable influence quantities or random temporal and spatial variations of influences. [0003] Systematic errors in physical measurement usually come from: (1) Instrument errors, which are caused by the...

AI Technical Summary

Problems solved by technology

However, this technical solution still has the following defects: (1) The pressure value measured by the piezoelectric ceramic sheet is the sum of the cycloid tension, the gravity of the bracket, the gravity of the pressure guide plate, etc., and the simple pendulum that conforms to the law of simple harmonic motion usually has a pendulum angle It is very small, no more than 5°. Therefore, during the motion cycle of the simple pendulum, the relative change range of the pressure measured by the piezoelectric ceramic sheet is very small, and then it is compared with the preset threshold after performing A / D conversion and losing a certain accuracy. As a result, the measurement accuracy is greatly reduced; (2) After changing the length of the cycloid, the pressure fluctuation range of the piezoelectric ceramic sheet will also change, and its preset threshold must also be adjusted accordingly. This adjustment also requires multiple tests. (3) The change of the vibration amplitude of the pendulum will not change the period of the pendulum, but it will affect the pressure measurement fluctuation range of the piezoelectric ceramic sheet, and the preset threshold value for comparison has to be determined. (4) The more fatal defect is that due to the essential properties of the piezoelectric ceramic sheet, the output piezoelectric signal loop is not coincide completely, while there is always a certain hysteresis, such as figure 1 As shown, this leads to an inherently inaccurate measurement of the period of a simple pendulum

However, when it is used to measure the period of a pendulum, the device still has the following theoretical defects: (1) the photogate must be strictly placed at the equilibrium position of the pendulum (the lowest point of the pendulum movement), but in fact it is very If it is difficult to strictly meet this condition, the photogate usually deviates from a certain distance, resulting in inaccurate period measurement; (2) when the photodiode sensor of the photogate is periodically blocked during the reciprocating motion of the ball, the light It cannot be blocked or moved away instantly, and the light intensity it receives varies with the process of swinging the ball from left to right and from right to left, but its output signal has a short-term transient process. As a result, the time points indicating the passage of the pendulum ball in different directions do not exactly correspond to the same position, which leads to a certain error in the period measurement of the simple pendulum in essence; (3) due to the limitation of the principle of the voltage comparator, During the reciprocating motion of the pendulum ball, the input signal of the voltage comparator changes from small to large, and from large to small. In these two opposite processes, the output signal of the voltage comparator cannot jump at the same voltage value point, but There is a certain hysteresis, which makes the period measurement of the simple pendulum inherently impossible to accurately determine

In this technical solution, there are still (including but not limited to) the following defects: (1) The PNP three-wire inductance normally open proximity switch is required to be strictly placed at the lowest point of the pendulum ball movement, which is actually difficult to strictly achieve this point , leading to inaccurate period measurement; (2) Inductive proximity switches also have hysteresis, that is, during the movement of the pendulum ball from left to right and from right to left, the switch opening and closing actions do not strictly occur in different directions of movement. The same position point, but a slight deviation, which is one of its essential properties, is an insurmountable defect, and it is difficult to accurately measure the period of a simple pendulum

[0022] It is worth pointing out that, from the theoretical analysis process, it can be seen that the above-mentioned various technical defects only exist in the periodic measurement of periodic reciprocating motion, and do not exist when the measured motion is unidirectional motion.

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