JPH0515328B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to the configuration of a digital voltmeter. In particular, the present invention relates to a digital voltmeter that can widen the range of measurement signals and can freely select required measurement conditions such as measurement speed and accuracy. [Prior Art] Conventional digital voltmeters have device configurations that are compatible with either high-speed measurement, high-precision measurement, or measurement requiring an integral effect, depending on the measurement application. Digital voltmeters that require high-precision measurements generally use an integral type analog-to-digital conversion circuit. This analog-to-digital conversion circuit integrates the input signal, so
Although the integration time is a little long, even if AC noise is superimposed on the input signal, by setting the time width of the analog integration period to an integer multiple of the AC period in advance, you can completely remove the effect, and random Since noise is also reduced at the same time, highly accurate measurements can be performed. Digital voltmeters that require high-speed measurements use weighted analog-to-digital conversion circuits (for example, weighting using a resistance ladder). This analog-to-digital conversion circuit includes a digital-to-analog conversion circuit as a component, and the whole constitutes one closed loop, and the digital signal generated by the control circuit is converted into an analog voltage by the digital-to-analog conversion circuit. ,
The digital output is compared with the input signal voltage sampled and held by the comparator, and the digital output is feedback-controlled so that the difference between the two is minimized. That is, the highest order digit (MSD) is first switched on, the input signal and the output of the digital-to-analog conversion circuit are compared, and if the former is greater, the process proceeds directly to the next digit. If the input signal is small, after switching off the highest digit (MSD),
Turn on the next digit. Thereafter, the same process is performed up to the lowest digit (LSD), and finally, when the control circuit reads out the on/off state of each digit, a digitized output is obtained. [Problems to be solved by the invention] However, such conventional digital voltmeters use an integral analog-to-digital conversion circuit that has extremely high accuracy and is resistant to noise such as AC power ripple. In this case, it takes a long time for the integral value to reach a stable point, and the measurement time must be extended. On the other hand, when using a weighted analog-to-digital conversion circuit that can perform high-speed measurements,
Although it is possible to construct a high-speed digital voltmeter compared to the case where a digital conversion circuit is used, there are problems such as that it is difficult to increase the accuracy because there is no integral effect. The present invention has been made by focusing on these conventional problems, and allows a single digital voltmeter to be used for high-speed measurement, high-precision measurement, or measurement that requires an integral effect. ,
The purpose is to provide a digital volt meter. [Means for Solving the Problems] The digital voltmeter of the present invention is characterized in that it includes an integral type analog-to-digital conversion circuit and a weighted type analog-to-digital conversion circuit, and includes means for switching between them. do. That is, an amplifier that amplifies an input analog signal, a weighted analog-to-digital conversion circuit that receives the output of this amplifier, and this analog/digital conversion circuit.
A digital/analog conversion circuit connected to the output of the digital conversion circuit, a differential amplifier whose inputs are the output of this digital/analog conversion circuit and the output of the above amplifier, and the output of this differential amplifier is connected to the weighted analog converter. a first means for measuring the voltage of the input analog signal, including means for forming a feedback loop for re-inputting the signal into the digital conversion circuit; and a second means for measuring the voltage of the input analog signal, which includes an integral type analog-to-digital conversion circuit having the output of the amplifier as input. Control and calculation that is connected to the voltage measuring means for the input analog signal and the outputs of the first and second voltage measuring means, calculates the voltage of the input analog signal from the respective outputs, and outputs the value to the display. A first mode in which the voltage of the input analog signal is measured only by the first means, and a second mode in which the voltage of the input analog signal is measured only by the second means. and a third mode in which the voltage of the input analog signal is measured by inputting the difference between the output measured by the first means and the input analog signal to the second means. It is characterized by having [Function] The digital voltmeter of the present invention has three operation modes that can be switched by a switch operation. In the first mode, when high-speed measurement is required, the slow integration type analog-to-digital conversion circuit is separated and only the high-speed weighting type analog-to-digital conversion circuit is configured. The second mode is when high precision measurement is required and is configured with only an integral type analog-to-digital conversion circuit.
Accuracy can be increased by lengthening the integration time.
Further, by selecting the integration time to be an integral multiple of the signal to be removed, an integration effect can be provided. Furthermore, the third mode uses a combination of a weighted analog-to-digital converter circuit and an integral-type analog-to-digital converter circuit to apply the integral effect only to the part that is necessary for the measurement signal. It is faster and more accurate than when measuring with . In other words, a weighted analog-to-digital conversion circuit measures the approximate value of the measured voltage,
The difference between the estimated value and the measured voltage is calculated using an integral analog
By measuring with a digital conversion circuit, high-speed and highly accurate measurements can be performed. [Example] Hereinafter, an example system of the present invention will be described based on the drawings. The figure is a block configuration diagram illustrating an embodiment of the present invention. In the figure, the input terminal 1 of the current proportional to the measured voltage is connected to the input of the amplifier 2,
The output of the amplifier 2 is connected to the input of a weighted analog-to-digital conversion circuit 4 via a changeover switch 3. The output of the weighted analog-to-digital conversion circuit 4 is connected to a digital-to-analog conversion circuit 5, and the output of the digital-to-analog conversion circuit 5 is connected to one input of a differential amplifier 6. The output of the amplifier 2 is connected to the other input of the differential amplifier 6, and the output of the differential amplifier 6 is connected to the changeover switch 3 and the integral type analog-to-digital conversion circuit 8. An open/close switch 7 is connected in parallel with the output of the differential amplifier 6 and the negative input. A control and arithmetic circuit 9 is connected to the outputs of the weighting type analog-to-digital conversion circuit 4 and the integral type analog-to-digital conversion circuit 8, and a display 10 for digitally displaying the measured voltage value is connected to the output. The changeover switch 3 has three switching modes: A, which connects the amplifier 2 and the weighted analog-to-digital conversion circuit 4; B, which connects the output of the differential amplifier 6 and the weighted analog-to-digital conversion circuit 4; This is C which does not provide input to the weighted analog-to-digital conversion circuit 4. A mode switching circuit 11 is connected to the control and calculation circuit 9 and controls the changeover switch 3 and the open/close switch 7. Next, the operation of the digital voltmeter of the present invention will be explained in three operation modes with reference to the table below. The first mode is for measurements that require the highest speed, the second mode is for measurements that require the highest precision, and the third mode is for optimal measurements with intermediate characteristics between these. be.

〔Effect of the invention〕

As explained above, the present invention combines a weighting type analog-to-digital conversion circuit and an integral type analog-to-digital conversion circuit to form one analog-to-digital conversion circuit to configure a digital voltmeter. For high-speed measurement, high-precision measurement, or a combination of these, the integration effect is applied only to the necessary part of the measurement signal, making it possible to perform faster measurements than if all measurements were performed using an integral type analog-to-digital conversion circuit. The user can freely select the most suitable conditions.

[Brief explanation of drawings]

The figure is a block configuration diagram showing one embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Input terminal, 2... Amplifier, 3... Changeover switch, 4... Weighted analog/digital conversion circuit, 5... Digital/analog conversion circuit, 6... Differential amplifier, 7... Open/close switch, 8
... Integral type analog-to-digital conversion circuit, 9...
...Control and arithmetic circuit, 10...Display device, 11...
...Operating mode switching circuit.

Claims (1)

[Claims] 1. A weighted analog-to-digital conversion circuit 4 whose input is given an analog voltage to be measured, a digital-to-analog conversion circuit 5 connected to the output of this analog-to-digital conversion circuit 4, and a A differential amplifier 6 that calculates the difference between the output of the analog conversion circuit 5 and the analog voltage to be measured.
and a first switch 3 that connects the output of the differential amplifier 6 to the input of the weighted analog-to-digital conversion circuit 4 instead of the analog voltage to be measured, A second voltage measuring means including an integral type analog-to-digital converter circuit 8 which inputs an analog voltage is provided, and further comprises an output of the weighted type analog-to-digital converter circuit 4 and an output of the above-mentioned integral type analog-to-digital converter circuit 8. A digital voltmeter is equipped with a control and arithmetic circuit 9 to which are respectively connected, and a display 10 to which the output of the control and arithmetic circuit 9 is given.
A second switch 7 is provided which connects the output of the differential amplifier 6 to the input of the switch, and the control and arithmetic circuit 9 switches and controls the first switch and the second switch to measure the analog voltage to be measured. A first mode in which the voltage is measured by the first voltage measuring means and the measurement result is displayed on the display; the first switch is opened, the second switch is closed, and the differential amplifier 6 a second mode in which the analog voltage to be measured is measured by the second voltage measuring means by inputting the output of the converter into the integral type analog-to-digital converter circuit, and the measurement result is displayed on the display; The first and second switches are controlled to apply the analog voltage to be measured to the input of the weighting type analog-to-digital conversion circuit 4, and to apply the analog voltage to be measured to the input of the integral type analog-to-digital conversion circuit 8 instead of the analog voltage to be measured. The above differential amplifier 6
and a third mode in which the output of the weighting type analog-to-digital conversion circuit 4 and the output of the integral type analog-to-digital conversion circuit 8 are displayed on the display. A digital voltmeter characterized in that the digital voltmeter is provided with a means 11 for switching between the three operation modes by operation.