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sensitivities. Its major disadvantages are that it requires large lens appertures
and high grade optical elements to obtain the necessary sensitivity and
resolution, and large angle measurements cannot be made because of inherent
ambiguities at the larger shifts.
K E engineers finally decided on the intensity comparison method
splitting the image of a target into 2 equal halves. Comparing the intensity
of each half with a photoelectric null device gives the zero positiondeviations
are indicated by the amount by which the bridge circuit is out of balance.
Disadvantage of the intensity comparison method is that it does require two
photo cells that have to be matched and that should not change properties
during measurements. Its advantage is that the instrument has no moving
parts, and is basically a simple design independent of the resolving power
which in general limits optical sensitivity.
Overgenomen uit Electrotechnical Design, September 1959.
