SU754320A1 - Dc digital voltmeter - Google Patents

Description

The invention relates to electrical engineering and can be used in digital devices for measuring constant voltage, current, and resistance.

There are digital DC voltmeters consisting of a preamplifier with a measuring circuit, a null organ, an amplifier-integrator, a clock generator, a pulse counter, a valve, and a device for matching the integration period with the power supply period [ΐ].

Such voltmeters provide the suppression of only symmetric periodical ’^ ci noise.

Also known are digital DC voltmeters containing a measuring circuit, the output of which is 20

connected to the first input of the dc amplifier, the output of the dc amplifier is connected to the second input of the measuring circuit and an analog-digital converter, a rectangular pulse generator, a resistor, a capacitor and the first modulator connected in series, a dc amplifier and a demodulator, controlled inputs dd

^{: the} first modulator and demodulator are connected to the first output of the square-wave generator AND.

In such a voltmeter, the interaction in the voltage modulator of the interference frequency and the modulating frequency produces a voltage of spurious side frequencies, which reduces the noise immunity of the device.

The aim of the invention is to improve the noise immunity.

This goal is achieved by the fact that a digital DC voltmeter containing a measuring circuit, the output of which is connected to the first DC amplifier input, the output of the DC amplifier is connected to the second input of the measuring circuit and analog-digital converter, square-wave generator, resistor, capacitor and in series the first connected modulator, an AC switching amplifier and a demodulator, the controlled inputs of the first modulator and the demodulator are connected to the first output of the generator right ol pulses provided by the adder, the second modulator pulse

3

754320

four

a second AC amplifier and a demodulator, the second modulator, an AC pulse amplifier and a demodulator are connected in series between the input of the first modulator and the second input of the adder, the adder is switched on by its first input between the output of the first demodulator and the second input of the DC amplifier, the controlled inputs of the second modulator and the demodulator is connected to the second output of the generator of rectangular pulses, and the output of the measuring circuit is connected via a resistor to the inputs of two modulators, the inputs of two modulators, in turn, are connected via a capacitor to the output of an adder, and the output of an analog-to-digital converter is connected to the input of a square-wave generator. ’

The drawing shows a block diagram of the device.

Voltmeter contains input terminal

I, connected to the first input of the measuring circuit 2, the first modulator

h, pulse amplifier 4 AC and demodulator 5, resistor 6, capacitor 7, DC amplifier 8, analog-digital converter 9, square wave generator 10, second modulator

II, an alternating current pulse amplifier 12 and a demodulator 13, and an adder 14.

The device works as follows.

The signals at the inputs of the modulators 3

and. 11 are converted into pulses that are amplified by alternating current pulse amplifiers 4 and 12. Demodulators 5 and 13 restore the DC component. Since the modulator 3 and the demodulator 5 work in phase, and with respect to the modulator 11 and the demodulator 13 - out of phase, the signals are added in the adder 14 with the restoration of the original form that took place at the inputs of the modulators 3 and 11. The parasitic switching pulses that occur when the modulators 3 and 11, amplified by amplifiers 4 and 12 and compensated for by the action of feedback through the capacitor 7, which leads to a decrease in the amplitude and duration of switching pulses arising in the modulators, reduces the parasites created by them tnye components-, t and _o and I from the detection of side frequencies.

The decrease in the absolute values of and _& and 1 _o leads to a decrease in their changes from the influence of temperature and in time. Thus, the noise immunity of the device increases, which makes it possible to increase its sensitivity in voltage and current, to expand the range of voltage measurements.

Claims (1)

Claim A digital DC voltmeter containing a measuring circuit, the output of which is connected to the first input of a DC amplifier, the output of a DC amplifier is connected to a second input of the measuring circuit and an analog-digital converter, a square-wave generator, a resistor, a capacitor and the first connected in series first modulator, pulse amplifier AC and demodulator, controllable inputs of the first modulator and demodulator are connected to the first output of the generator of rectangular pulses, which Because, in order to improve noise immunity, it is equipped with an adder, a second modulator, a switching amplifier of alternating current and a demodulator, the second modulator, a switching amplifier of alternating current and a demodulator connected in series between the input of the first modulator and the second input of the adder, the adder is switched on with its first the input between the output of the first demodulator and the second input of the DC amplifier, the controlled inputs of the second modulator and the demodulator are connected to the second output of the rectangular generator and pulses, and the output of the measuring circuit is connected through a resistor to the inputs of two modulators, the inputs of two modulators, in turn, are connected through a capacitor to the output of the adder, and the output of the analog-digital converter is connected to the input of a rectangular pulse generator.