JP2940010B2 - Broadband power meter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power meter that performs digital arithmetic processing when the frequency of a signal under measurement is wide.

〔Overview〕

The present invention relates to a wideband wattmeter that obtains power by digital operation by inputting a voltage signal and a current signal of a signal under measurement as input, measuring the frequency of the signal under measurement, and determining the number M of repetitive samplings according to the result. Thus, a predetermined measurement accuracy can be obtained with a simple circuit, and the measurement time is shortened.

[Conventional technology]

Conventionally, it has two digital-to-analog converters that receive the voltage signal and the current signal of the signal under test, respectively, and repeatedly samples and multiplies each output over time with a period shorter than the period of the signal under test. 2. Description of the Related Art A wideband power meter is known which includes a data processing circuit using a microprocessor which executes and averages the result. In such a device, unless the sampling frequency of the digital-to-analog conversion circuit is an integer multiple of the frequency of the signal under test, as shown in FIG. Will occur. This causes a measurement error.

For this reason, in the conventional equipment, the digital-to-analog conversion that sets the sampling frequency to follow an integer multiple of the frequency of the signal under test, sets the sampling frequency extremely higher than the frequency of the signal under test, and reduces the effect of the fraction, There is a technique in which sampling by a circuit is repeatedly performed over a large number of cycles of a signal to be measured, the result is stored, and an averaging process is executed to reduce the influence of a fraction.

[Problems to be solved by the invention]

In the prior arts described above, the measurement accuracy can be improved, but in the above, a phase-locked oscillator is required to make the sampling frequency generated in the measuring instrument follow the frequency of the signal under measurement, In addition, the phase-locked oscillator must be a high-grade one that can operate over a wide frequency range. For the above, setting a high sampling frequency requires a high-speed analog-to-digital conversion circuit. Since the measurement is performed many times, the time required for measurement becomes longer, and the like.

The present invention is to improve the above-mentioned prior arts and the above-mentioned ones, since the circuit is basically expensive, which is avoided. That is, according to the present invention, the clock signal frequency for sampling does not need to variably follow, eliminating the need for a high-speed analog-to-digital conversion circuit.
An object of the present invention is to provide a wideband power meter that can reduce the time required for measurement using a simple circuit.

[Means for solving the problem]

The present invention focuses on the fact that when the measurement accuracy is set, the number of periods of the signal under measurement to be repeated to obtain the measurement accuracy becomes constant. That is, the present invention is characterized in that the frequency of the signal under measurement is measured, and the number of repetitions M is set in accordance with the measured frequency.

The present invention is characterized in that it includes means for measuring the frequency of the signal under measurement, and means for determining the number of repetitions M of sampling according to the measured frequency.

In the device according to the invention, the sampling frequency generated in the measuring device is in principle fixed at a frequency at which the oscillator can be manufactured inexpensively. However, when the measurement accuracy is made variable, it can be configured to switch over a small number of fixed frequencies according to the measurement accuracy.

[Action]

In the present invention, in order to simplify the circuit, the clock signal frequency must be at least measured (eg, 1 MHz) for its measurement.
To). On the other hand, the measurement accuracy is set to a certain value (for example, ± 1
%), If the sampling frequency is more than several times the frequency of the signal under measurement, the value gradually progresses to the true value each time the number of measurements is repeated. Therefore, sampling and multiplication should be repeated to obtain the measurement accuracy. The number of periods of the signal under measurement is determined to be a fixed value (for example, 20 periods). Therefore, the required number of sampling repetitions is inversely proportional to the frequency of the signal under measurement.

The apparatus of the present invention automatically measures the frequency of the signal under measurement at the beginning of the measurement, and sets the number of repetitions M of sampling in accordance with the frequency. Therefore, sampling and calculation can be completed in the shortest time required to obtain the set measurement accuracy.

〔Example〕

FIG. 1 is a block diagram of the apparatus according to the embodiment of the present invention.
This apparatus has a voltage input terminal 11 and a current input terminal 21 to which a signal to be measured having a wide range of frequencies is input, and a signal of the voltage input terminal 11 and a signal of the current input terminal 21 which are respectively input to perform analog processing. Input circuits 13 and 23, and two analog-to-digital conversion circuits each receiving the output of each of the input circuits 13 and 23 as an input.
15 and 25, a data processing circuit 31 including multiplication means for multiplying each sampling output of the two analog / digital conversion circuits 15 and 25, a display circuit 35 for displaying the output of the data processing circuit 31, An external output terminal 37 is provided.

The data processing circuit 31 includes a microprocessor (not specifically shown in FIG. 1) for executing program processing, the microprocessor including the multiplication means, and the multiplication means changing over time. Means for repeatedly multiplying the sampling outputs of the two analog-to-digital conversion circuits by a plurality of M times, means for storing the results of the M times, and an average value of the results of the M times stored in the means for storing Means for calculating

Here, as a feature of the present invention, this data processing circuit includes means for measuring the frequency of the signal to be measured from the output signals of either of the two analog-to-digital conversion circuits 15 or 25, and according to the measured frequency. The number of times M
Means for determining

The clock signals supplied to the two analog / digital conversion circuits 15 and 25 and the data processing circuit 31 are supplied from a clock signal generation circuit 33, and their frequencies are set to be fixed. In this embodiment, it is 1 MHz.

FIG. 3 is a flowchart showing the operation of the main part of the microprocessor incorporated in the data processing circuit 31. That is, when the apparatus starts measurement, it measures the frequency of the signal under measurement at the beginning. The required number of samplings M is determined according to the measurement result. This is configured such that a table in which the number of times M is made to correspond to each frequency range is built in, and when the measurement result of the frequency is obtained, the number of times M is determined with reference to this table.

When the number of times M is determined, a voltage sampling value Vm and a current sampling value Am from two analog-to-digital conversion circuits 15 and 25 that are sequentially input are multiplied and stored. This operation is executed M times for a sampling value that changes with the passage of time. When M multiplications are completed, an average value is calculated from the stored multiplication results, and this is displayed as a measurement result.

 Next, the number of repetitions M will be described.

Now, the specification of the wideband power meter is set to a frequency range of 10 Hz to 100 kHz in consideration of versatility. On the other hand, as the frequency of the oscillator of the clock signal generation circuit 33, 1 MHz is selected as a frequency at which stable operation can be expected at low cost. Then, even at the maximum frequency of 100 kHz, sampling can be performed ten times in one cycle of the signal under measurement. Under this condition, the frequency of the signal under measurement is changed, and when the sampling frequency is not an integral multiple of the frequency of the signal under measurement, that is, when a fraction occurs as shown in FIG. It was investigated to what extent the effect of the fraction could be reduced by performing. Now, when a simulation is performed with the specification of the wideband power meter set to a measurement accuracy of ± 1%, it is understood that the accuracy of the specification is satisfied when sampling and averaging are performed for approximately 20 cycles of the signal under measurement. That is, it can be seen that the number of executions of the sampling and the averaging operation satisfying the specifications is substantially constant. The 20 periods correspond to about 2 seconds when the frequency of the signal under measurement is near the lowest frequency (10 Hz), and correspond to about 0.2 millisecond when the frequency of the signal to be measured is near the highest frequency (100 kHz).

Therefore, when the frequency of the signal under measurement is low, it takes about 2 seconds to perform the measurement, but when the frequency of the signal under measurement is high, there is no need to wait for this time, and the result is displayed in a short time. However, the accuracy is sufficiently satisfied.

The apparatus of the present invention measures the frequency of the signal under measurement at the beginning of the measurement, sets the number of repetitions M according to the measurement result, and repeats sampling up to the number M. The relationship between the measured frequency to be measured and the number of times M is set, for example, as shown in the following table, and is prepared in advance as a table in the ROM, and the number of times M is determined with reference to each frequency measurement. In this table, M is the number of times of repeated sampling, and T is the time required for performing this repeated sampling. Therefore, from the start of the measurement to the time when the result is displayed, it takes a sum of the time T and a slight time for measuring the frequency.

In this way, the apparatus of the present invention can obtain a measurement result in the shortest time required according to the frequency of the signal under measurement.

The division of the frequency range exemplified in the above table can be further practically rationalized by further refining the division particularly in a low frequency range.

In the above embodiment, the frequency of the clock signal is fixed. However, a small number of clock signals such as two or three may be provided, and the frequency may be switched and used. In that case, a device that makes the measurement accuracy variable can be realized. As an example, a clock signal frequency of 2 MHz is provided in addition to the above-mentioned clock signal frequency of 1 MHz, and the user can switch and use the clock signal frequency. With this configuration, when 2 MHz is selected, the measurement accuracy can be improved to approximately ± 0.5%. If the number of clock signal frequencies that can be selected is too large, there is no practical meaning and the device becomes expensive.

[Effects of the Invention] As described above, according to the present invention, the accuracy can be improved by using inexpensive circuit elements without using a variable frequency oscillator and without using a high-speed analog-to-digital converter. High-bandwidth wattmeter can be realized. In the apparatus of the present invention, the signal to be measured is repeatedly sampled as time elapses, but the time required for measurement is determined rationally by the frequency to be measured for each measurement accuracy, and can be set to the minimum required time. Therefore, the time required for the measurement can be reduced as a whole.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention. FIG. 2 is a diagram for explaining a relationship between a signal under measurement and a sampling period. FIG. 3 is a flowchart showing the operation of the main part of the data processing circuit of the device according to the embodiment of the present invention. 11 ... voltage input terminal, 13 ... input circuit, 15 ... analog-digital conversion circuit, 21 ... current input terminal, 23 ... input circuit, 25 ... analog-digital conversion circuit, 31 ...
Data processing circuit, 33 ... Clock signal generation circuit, 35 ...
Display circuit, 37 Output terminal.

Claims (1)

(57) [Claims] 1. A voltage input terminal and a current input terminal to which a signal to be measured having an indefinite frequency is inputted, two analog / digital conversion circuits each receiving the signal of the voltage input terminal and the signal of the current input terminal, respectively; A data processing circuit including a multiplying means for multiplying each sampling output of the two analog-to-digital conversion circuits, wherein the data processing circuit controls the multiplication means to sample the two analog-to-digital conversion circuits over time. A wide-band power meter including: means for repeatedly multiplying the output a plurality of times M; means for storing the result of the M multiplications; In the data processing circuit, means for measuring the frequency of the signal under measurement, and Means for determining the number of times M by referring to a table in which the value of the M corresponding to the frequency of the signal under test is stored, and supplied to the two analog-digital conversion circuits and the data processing circuit. A wide-band power meter, wherein a plurality of frequencies of a clock signal are set to be selectively switchable.