2.3　Compensation

The compensation is to offset(or compensate)the effect of the measured physical quantity by adjusting one or several similar standard physical quantities in a known balance relationship(or known value)with the measured physical quantity,which can put the system in a state of compensation(balance).For the measuring system operating at the compensation state,the measured value has a defined relationship with the standard quantity,leaving that value measurable.This measuring method is called the compensation.The characteristic of the compensation is that the measuring system contains a standard measuring tool and a zero pointing device.During the measurement,the measured quantity is directly compared with the standard quantity,and the standard quantity can be adjusted so that the difference between the standard quantity and the measured quantity can be eliminated.This process is called compensation or balance operation.

Figure 2.3.1 is a typical schematic diagram of measuring the electromotive force by compensation.In this figure,E0 is a continuously adjustable standard power supply,Ex is the power supply to be tested,and G stands for a galvanometer.Adjust the amplitude of E0 to make the galvanometer G point to approach to zero.At this very moment,the circuit operates in the compensation state when Ex=E0,which indicates that the electromotive force of the tested power supply can be determined.Similarly,the compensation principle can also be used in other experiments,such as the resistance measurement with a balanced bridge and weight measurement with a balance.

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Figure 2.3.1　Principle diagram of measuring electromotive force by compensation method

The advantage of the compensation is that it can eliminate some constant systemic errors and obtain relatively high accuracy.However,the measuring process of this method is relatively complicated,and the necessary compensation should be performed in advance.