This paper describes a trial construction of an interferometric standard barometer, the main aim of which is to measure without any break the pressure within the range between 0 and 800mmHg with an accuracy of ±1μHg.
Essentially, it is a combination of two modified Michelson's interferometers and two levels of mercury in a stainless-steel U-tube are located by means of white light interference. Any relative displacemet between the two levels is transferred to a single displacement of a horizontally sliding stock by aid of an appropriate optical system. (Fig. 2)
Operating process is as follows. At first, in order to obtain the datum point, N is closed V and P are opened to an atmospheric pressure, and the datum point reading "X
0" is determined. Next, V is closed, N is opened to vacuum and thus the difference in heights of mercury columns or h arises. Then, D is driven towards S until white light interference fringes become visible again. If the fringes caused by the upper mercury level become visible at "X
1" and those by the lower level at "X
2", h is given by
h=(X
1+X
2-2X
0)+ε
where ε is a correction due to the vacuum space existing above the upper mercury level.
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