Comparators are those instruments which can be used to compare, generally, linear dimensions of similar components with a slip gauge standard.
Features:
Comparators have no built in standards of their own; they indicate only the differences in size between the nominal dimension set on the comparator by SLIP Gauges and the dimension of the component being measured.
They have precisely engineered mechanisms used in the principle of its operation.
They can be built to give a magnification as high as X50000
They are so designed to allow smallest scale division of 0.00025 mm
In principle a comparator works on relative measurements, i.e., it gives only dimension difference in relation to a basic dimension.
So, a comparator is to compare the unknown dimensions of a part with some standard or a master setting which represents the basic size and the dimensional variations from the master setting have to be amplified and measured.
The function of a comparator is to detect to a high degree of precision the small difference, if any, between a suitable length standard ad the measured part.
In construction, a comparator consists of three essential elements:
- A sensing device, usually, a plunger, which faithfully senses the input signal represented in this case by a change of length or a surface displacement.
- A magnifying or amplifying system to increase the signal to suitable magnitude.
- A display system (usually a scale and pointer) which utilizes the amplified signal to provide a suitable readout.
Desirable Characteristics of a good comparator:
The fundamental requirements o be fulfilled by every comparators are as follows:
1. Robust in design and construction: in order to withstand ordinary usage to maintain consistent measuring accuracy.
2. Indicating device used shall be such as to show readings at least possible time, for which the magnification system should be such as to get readings dead beat.
3. Provision for compensation against temperature effects.
4. Scale must have linear characteristic.
5. Though sensitive, the instrument should be rigid enough to accommodate mishandling to some extent without permanent harm.
6. Should have maximum versatility, to accommodate to be used for measuring wide range of dimensions.
Uses of Comparators:
a) In mass production, where components are to be checked at very fast rate.
b) As laboratory standards from which working or inspection gauges are set and calibrated/correlated.
c) For inspecting newly purchased gauges.
d) As working gauges, in some machines, for stage inspection of parts produced. This prevents rejection and ensured maintenance of tolerances at various stages of manufacturing.
e) For grading of parts into groups depending on their tolerances, for use in selective assembly of parts.
