What Is an Absolute Scale?

Absolute measuring method refers to a measurement method in which the measured quantity can be read directly from the instrument. Its characteristic is that the measured quantity can be directly compared with the standard quantity.

Absolute measuring method refers to a measurement method in which the measured quantity can be read directly from the instrument. Its characteristic is that the measured quantity can be directly compared with the standard quantity. For example, use a line ruler to measure the length, a vernier caliper to measure the diameter of the nut, and a graduated straw to measure a certain volume of liquid.

The absolute measurement method is a measurement method that focuses on the absolute value of the parameter, while the relative measurement method mainly focuses on the increment during stepping.

Absolute detection refers to: the position of each measured point is counted from a fixed zero point; incremental position detection refers to: measure only the displacement increment, and output a pulse wave every time a position is detected to move a basic unit Or sine wave, the displacement can be obtained by counting pulses.

Direct measurement means that the object measured by the position detection device is the object itself. The detection method of indirect measurement of the linear displacement of a machine tool using a rotary detection element installed at the motor or screw shaft end is called indirect measurement.

Measure the radioactivity of an element

The method of measuring radioactivity varies with the radionuclide. According to the measurement method, it can be divided into two categories. One is direct measurement with a measuring device

The decay rate of radionuclides does not need to rely on comparison with other measurement standards. This type of method is called absolute measurement. The other is relative measurement, that is, the measurement device needs to be calibrated with the help of other measurement standards, and the calibrated measurement device is used to measure the decay rate of the radionuclide. ^[1]

In recent years, countries have successively studied the absolute measurement method of radon activity and adopted it as a new standard radon activity measurement method. The double-filter membrane radon measurement method can be considered as an absolute radon measurement method in principle. It was invented and created by Americans and became popular in the United States in the 1970s. Thomas made a theoretical derivation of it in 1972, which brought the method to a relatively perfect level ^[2] . In 1996, the French National Laboratory of Ionizing Radiation (LaboratoirePrimaire des Rayonnements Ionisants, LPRI) first proposed a new absolute measurement method of ²²² Rn activity: in a vacuum environment, the radon generated by a standard radium source was condensed in a condensation On the tray, a small solid angle measurement of the condensation source using an alpha semiconductor detector can accurately obtain the energy spectrum and count rate of the solid radon source and its daughter particles after condensation, so as to achieve an absolute measurement of radon activity ^[3] . The uncertainty of the radon activity measurement results obtained in this experiment is less than 0.5% ^[4] . In 2001, Ingo Busch, a German PTB laboratory, used a proportional counter tube for absolute measurement of ²²² Rn. This method filled radon gas into a multi-electrode proportional counter (MEPC) with a special electrode structure at the end to measure radon. The alpha particle ionization of gas production is proportional to the electric pulse signal generated by the gas in the counting tube, and the energy spectrum obtained by computer-assisted processing is used to achieve absolute measurement. The uncertainty of the measurement method is less than 2% ^[5] .

In China, the research on the absolute measurement method of radon activity is still in its infancy. In 2005, the School of Nuclear Science and Technology of Nanhua University in order to solve the problem that ²²⁰ Rn and its daughters could not establish a radiation equilibrium state during the measurement process, it was difficult to establish a ²²⁰ Rn standard For the measurement device, a special structured ZnS (Ag) small scintillation chamber was developed for absolute measurement of ²²⁰ Rn. This measurement method improves the general scintillation chamber so that the detection efficiency of ²²² Rn / ²²⁰ Rn and its daughter alpha particles is 100%. ^[6]

Absolute measurement method for condensing small solid angle has the lowest relative uncertainty of the measurement result (<1%), high energy resolution, convenient gas transmission, convenient application in the chamber, and can also be used as a standard after dispensing The gas source is directly calibrated. However, the method has high equipment cost, high requirements on experimental conditions for maintaining a low-temperature vacuum state, and relatively complicated operation. The multi-electrode proportional counting tube activity absolute measurement method device is relatively simple, the proportional counting tube measurement method is mature, and the relative uncertainty of the measurement result is relatively low (<2%). Although this method solves the problem of correction of the end effect to some extent by adding multiple ring electrodes, and studies the correction of the dead time, background, discrimination threshold, and wall effect, it also includes absorption effects in the experiment. The influence factors of uncertainties, such as the power accumulation effect, have no room for improvement. The method for absolute measurement of radon activity in small scintillation chambers is simple, the principle of the method is mature, the sampling speed is fast, and there is less interference from factors such as ambient temperature and relative humidity. However, this method cannot measure the alpha spectrum of tritium, so it cannot distinguish the spectral characteristics of tritium and its progeny. At the same time, the method is affected by the complicated structure, the change of the diameter of the connecting pipe, and the manufacturing process. There is room for improvement and improvement, and there is room for further research. ^[1]

Absolute measurement of capacitor loss factor

The Chinese Academy of Metrology uses the vacuum variable-gap capacitor method, which has absolutely eliminated the loss factor of standard capacitors in the range of 60 KHZ ~ 10kHz.

The side is fixed and verified by the ring cross capacitor method. Both methods measure the loss factor (at 1kHz) of a 1pF capacitor at the same time, and the difference is only 2 x 10 ^-7 . The uncertainty of the measured loss factors of the 10pF, 100pF, and 1000pF capacitors (at 1KHZ) is 1 x 10 ^-7 , 1.5 x 10 ^-7, and 3 x 10 ^-7 , respectively. The developed absolute loss factor measuring device includes three parts: a set of variable gap capacitors (1 ~ 10pF, 10 ~ 100pF, 100 ~ 1000pF) with a vacuum system; those with auxiliary branches at high and low potentials Transformer bridge; a set of sealed nitrogen-filled standard capacitors (4 each of 1, 10100 and 1000 p F); and a toroidal cross capacitor (1 pF) for side-effect experiments.

Absolute measurement of optical homogeneity of optical materials

Optical uniformity is an important indicator of optical materials. High-precision measurement methods generally use absolute measurement methods, and the method has complicated steps and is easily affected by the environment. According to the phase-shifting characteristics of the wavelength phase-shifting interferometer, a two-step absolute measurement method of wavelength tuning for measuring the optical uniformity of optical materials is proposed. In this method, the optical uniformity of the parallel plate is obtained by two steps of placing the parallel plate in the wavelength shifting interferometer and measuring the cavity. After the simulation is used to verify the correctness of the method, an experimental study is carried out and the measurement results are compared with the traditional absolute measurement method. The results show that the two-step absolute measurement method of wavelength tuning can be used to measure the optical uniformity of parallel plates, and the measurement steps are simple and the accuracy is high. ^[7]