A comparator works on relative measurements, i.e. to say, it gives only dimensional
differences in relation to a basic dimension. So a comparator compares the unknown dimensions of a part with some standard or master setting which represents the basic size, and dimensional variations from the master setting are amplified and measured.
Advantages of comparators:-
1. Not much skill is required on the part of operator in its use.
2. The calibration of instrument over full range is of no importance as comparison is done with a standard end length.
3. Zero error of instrument also does not lead to any problem.
4. Since range of indication is very small, being the deviation from set value, a high magnification resulting into great accuracy is possible.
The comparators are generally used for linear measurements, and various comparators available differ principally in the method used for amplifying and recording the variations measured.
Classification of comparators:-
1. Mechanical comparators
2. Mechanical-optical comparators
3. Electrical and Electronic comparators
4. Pneumatic comparators
5. Fluid displacement comparators
6. Projection comparators
7. Multi-check comparators
8. Automatic gauging machines.
Characteristics of Comparators:-
Before we discuss the various types of comparators, let us first look into various fundamental requirements which every comparator must fulfill. These are as follows:
1. The instrument must be of robust design and construction so as to withstand the effect of ordinary usage without impairing its measuring accuracy.
2. The indicating device must be such that readings are obtained in least possible time and for this, magnification system used should be such that the readings are dead beat. The system should be free from backlash, and wear effects and the inertia should be minimum possible.
3. Provision must be made for maximum compensation for temperature effects.
4. The scale must be linear and must have straight line characteristic.
5. Indicator should be constant in it return to zero.
6. Instrument, though very sensitive, must withstand a reasonable ill usage without permanent harm.
7. Instrument must have the maximum versatility, i.e., its design must be such that it can be
used for a wide range of operations.
8. Measuring pressure should be low and constant.
Uses of Comparators:-
The various ways in which the comparators can be used are as follows:-
1. In mass production, where components are to be checked at a very fast rate.
2. As laboratory standards from which working or inspection gauges are set and correlated.
3. For inspecting newly purchased gauges.
4. Attached with some machines, comparators can be used as working gauges to prevent work spoilage and to maintain required tolerances at all stages of manufacturing.
5. In selective assembly of parts, where parts are graded in three or more groups depending upon their tolerances.