The Use and Calibration of the Kern ME5000 Mekometer - SLAC ...

--
1.2. Path Length Modification
ME5000 Operation
The Kern ME3000 Mekometer eliminates the fractional part f by changing the patb distance D until
the phase difference is zero, indicating an integral number of half-wavelengths, (5) and Fig. 2.
D+6D = mf (5)
< D .f SD+
< m.?J2 >
FIGURE 2. Distance determination by changing the parh lengrh
As in the first approach, m is found by repeating the measurement using several predefmed
frequencies.
1.3. Frequency Modification
The Kern MESO& Mekometer also eliminates the fractional part f, but by using a different method.
The frequency is changed until a zero phase difference is obtained, (6) and Fig. 3.
?b
= m.-
D 2
(6)
< D >
FIGURE 3. Distance determination by changing the frequency
The value of m is found in a manner different from the frrst two approaches. The frequency is
increased in small steps until a zero phase difference is again detected, at which frequency the path
contains m+l of these new half-wavelengths X1/2,
D = (m+l)$ (7)
These two frequencies provide sufficient information to resolve m and thus the distance.
10