Use the sensor to measure the relative pressure coefficient of the air); disconnect the sensor from the vacuum pump, and read the output voltage U0 of the sensor at this time. U. is caused by the drift of the sensor's zero point and sensitivity with temperature changes. Subtract Um from U., and compare the difference with the atmospheric pressure to get the ratio between the voltage value and the atmospheric pressure value, that is, the Kp. calibration process ends here, and then officially starts: the input voltage is 5.011V, the vacuum degree is from Change from 100 to 20, with 5 as a change unit. Measure the relative air pressure coefficient value corresponding to each vacuum degree (Note: The air relative pressure coefficient value shown in the table has been corrected with v/V=0.02 to eliminate the change in the volume of the glass bubble and the uneven temperature of the gas in the duct The error caused). It can be seen from the data in the table that the measured value of the relative air pressure coefficient keeps increasing with the decrease of the vacuum degree and deviates more and more from its true value. The relationship between the two changes is shown.

The degree of vacuum () the relative pressure coefficient of air. The degree of vacuum () the relative pressure coefficient of air. The degree of vacuum () the relative pressure coefficient of air. The input voltage is changed from 2V to 9V. The influence of the vacuum degree on the measured value of the relative pressure coefficient of air shows the same trend. . For example: when the input voltage is 8.005V, the measured values ​​of the vacuum degree and the relative air pressure coefficient are shown in Table 2. The influence of the vacuum degree on the air relative pressure coefficient is as shown.

Vacuum degree () air relative pressure coefficient vacuum degree () air relative pressure coefficient vacuum degree () air relative pressure coefficient can reach the value when the vacuum degree is 100, and when the input voltage is 8.005V, the vacuum degree vs. the air relative pressure coefficient The same experiment was performed on other instruments in the laboratory, and the same results were obtained. In order to reduce the error caused by the vacuum pumping problem, the measured air relative pressure coefficient value can be multiplied by the corresponding vacuum The degree of correction of the experimental results. Take the vacuum degree of 95 as an example to illustrate: the vacuum degree directly affects U. When the vacuum degree is 95, the step after dividing by 95 is the process of drawing the PT diagram to find the slope (the slope is the relative air pressure coefficient). Since the slope = A'/AT, the slope and the 'are linear, the heart ttX 95 can be converted to directly multiply the slope by 95, because the intercept P. of the line on the Y axis changes very little, so you can directly The obtained relative air pressure coefficient value is multiplied by 95 to correct the error caused by insufficient vacuum. In summary, multiplying the obtained relative air pressure coefficient value by its corresponding vacuum degree can be corrected due to insufficient vacuum. Error. For example, the input voltage is 5.011V, the vacuum degree is 95, and the measured air relative pressure coefficient value is 0.0038899. The relative error between this value and the true value is 6.28. If this value is multiplied by the vacuum degree, it is 0.0038899X0. 95=0.0036954, the relative error between the corrected value and the true value is reduced to 0.97. This conclusion can be a good correction to the experimental results when the vacuum degree is not too low. When the vacuum degree is too low, various effects The influence of factors on the experimental results is more obvious. Simply correcting the vacuum degree cannot obtain accurate experimental results. However, in general, the vacuum pump in the laboratory will not have too low vacuum. Therefore, for daily student experiments, this conclusion The error caused by insufficient vacuum can be corrected well.

From the above discussion, it can be concluded that the lower the vacuum degree of the vacuum pump, the larger the value of the relative air pressure coefficient measured by the experiment, and the more it deviates from its true value 0.00366K-1. The change of the measured value of the air relative pressure coefficient varies with the degree of vacuum Increases and decreases continuously, showing a curve relationship with a gradually decreasing slope between the two. The experiment can correct the experimental results by multiplying the final measured air relative pressure coefficient by its corresponding vacuum value. .