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Paragraph 6 Output circuit (Value-voltmeter)

Original text. Later amendments are not shown.

(1)

Linearity

The performance of the rectifier and of any associated circuits of the valve-voltmeter shall be such that the current through the indicating meter is linearly related to the sinewave voltage input to the rectifier, to within ± 10 per cent. of that voltage, for all values of input voltage from 0.5 to 2.5 times the value producing reference deflection.

The application to the input of the rectifier of the sinewave voltage which produces reference deflection shall cause an increase of 1.75 volts ± 10 per cent. in the steady voltage across the rectifier load.

The increase in the sinewave voltage at the input of the rectifier required to increase the meter reading from reference deflection to full-scale deflection shall be not less than 5.5 db, nor more than 6.5 db.

(2)

Charge time-constant

A sinusoidal voltage of frequency equal to the intermediate frequency, which when continuously applied to the input terminals of the intermediate frequency amplifier produces reference deflection, shall, when suddenly applied at the same point, cause the change of voltage across the output circuit of the rectifier to reach 0.63 times the final value of the change of voltage in not less than 0.8 milliseconds and not more than 1.2 milliseconds.

In this test, the input terminals of the I.F. amplifier shall be disconnected from the preceding circuits of the measuring apparatus.

(3)

Discharge time-constant

The time taken for the current in the meter circuit to decrease by 0.63 times its initial value after an applied voltage as specified in 6 (2) above is suddenly removed shall be not less than 450 milliseconds and not more than 550 milliseconds.

(4)

Indicating meter

The indicating meter shall be of the permanent magnet moving-coil type in which the deflection of the needle is directly proportional to the current passing through the meter. Under the conditions of use of the measuring apparatus the damping of the meter shall be such that when a current of a value which produces a final steady full-scale deflection is suddenly applied to the meter, the time of rise to 80 per cent. of full-scale deflection is not less than 240 milliseconds and not more than 360 milliseconds and the overswing is less than 5 per cent. of the full-scale deflection.