JPH047473B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a ripple voltage measuring device improved to reduce the time required to measure the ripple voltage contained in the output of a regulated DC power supply.

[Technical background of the invention]

The easiest way to measure the ripple voltage superimposed on a DC voltage is to set the oscilloscope's input to AC, cut off the DC, and observe the waveform with the required sensitivity. The equivalent circuit in this case is shown in FIG.

That is, the input terminal 1 is led to a capacitor 2 of relatively large capacity, the direct current is cut off, the DC potential is set again by the resistor 3, and the input terminal 1 is led to the DC amplifier 4. A ripple waveform can be obtained by driving the Y axis of the cathode ray tube 5 with the output of the DC amplifier 4 and using a sweep signal that separately drives the X axis.

[Problems with background technology]

However, in this method, the ripple voltage to be measured is usually extremely small compared to the DC voltage superimposed thereon, and the gain of the DC amplifier 4 is set high. When the input terminal 1 is connected to or disconnected from the output terminal to be measured, the voltage at the input terminal 1 changes as shown in FIG. 2a.

At the moment when the input terminal 1 is connected to the output terminal to be measured, the capacitor 2 passes a step-like voltage change. Until the capacitor 2 is sufficiently charged, direct current cannot be completely cut off, and a portion of the direct current component is transmitted to the direct current amplifier 4, with the capacitor output becoming as shown in FIG. As a result, as shown in FIG. 2b, the light falls outside the display range L of the cathode ray tube 5.

When the capacitor 2 is sufficiently charged, the direct current is completely cut off and enters the display range L of the cathode ray tube 5. However, the time required during this time is from several seconds to more than 10 seconds, and the time required for the original measurement is 2 to 10 seconds. Compared to 3 seconds, this is a large loss of time. If the above-mentioned loss time can be eliminated, work efficiency in inspecting DC stabilized power supplies can be improved.

[Purpose of the invention]

This invention was made in order to eliminate the above-mentioned drawbacks, and when measuring minute ripple voltages superimposed on direct current, it is possible to instantly cut the direct current voltage and immediately measure ripple voltage. The purpose of the present invention is to provide a ripple voltage measuring device for measuring ripple voltage.

[Summary of the invention]

The ripple voltage measuring instrument according to the present invention samples an input analog signal at a predetermined sampling period and converts it into a digital signal, and calculates a difference between digital values having a time difference of one sampling period, and this difference between the digital values is used as a reference. By configuring the cumulative total of digital value differences to be cleared when the difference is greater than a threshold value, a DC voltage that is larger than the ripple voltage to be measured is cut off.

[Embodiments of the invention]

Embodiments of the ripple voltage measuring device of the present invention will be described below with reference to the drawings. FIG. 3 is a block diagram showing the configuration of one embodiment. In FIG. 3, a voltage applied to an input terminal 11 is input to an analog/digital converter 12 (hereinafter referred to as an A/D converter). This A/D converter 12, memory 13, accumulation register 1
4. Digital/analog converter 15 (hereinafter referred to as
A clock signal 17 from a clock generator 16 is input to each of the D/A converters.

This clock signal 17 causes the A/D converter 1 to
Reference numeral 2 converts the input voltage into a digital signal, and the output thereof is sent to the memory 13.

The output of the memory 13 is sent to a subtracter 18. The subtracter 18 performs subtraction using the results of two samplings of the input voltage, that is, the results of sampling with a time difference of one sampling period.
9 and an adder 20. The output of adder 20 is adapted to be sent to accumulation register 14.

Further, the comparator 19 compares the output of the subtracter 18 with a threshold set by a predetermined threshold value setter 21, and when the absolute value of the output of the subtracter 18 is greater than the threshold, clear signal 22 is sent to the accumulation register 14. It is now being sent to

The output of this accumulation register 14 is sent to the D/A converter 1.
It is set to be sent on 5th. D/A converter 1
The output of 5 passes through the low-pass filter 22 to the output terminal 2.
It is starting to be taken out from 3.

Next, the operation of the ripple voltage measuring device of the present invention configured as described above will be explained. now,
The voltage applied to the input terminal 11 is the voltage applied to the A/D converter 1.
2, and in this A/D converter 12,
It is sampled at a constant cycle by the clock signal 17 and converted into a digital quantity. The digital output of the A/D converter 12 is supplied to a memory 13 that stores data for two samplings, and is stored there.

The subtracter 1 calculates the difference between the current sampling result and the previous sampling result stored in the memory 13.
8, and the result is sent to a comparator 19 and an adder 20.
supply to.

The comparator 19 calculates the absolute value of the output of the subtracter 18 and compares it with the threshold value supplied from the threshold value setter 21. If the absolute value of the output of the subtracter 18 exceeds the threshold value, the comparator 19 clears the output value of the subtracter 18. A signal 22 is sent to the accumulation register 14 to clear the accumulation register 14.

The adder 20 and the accumulation register 14 constitute an accumulator, which accumulates the input data of the adder 20 in synchronization with sampling. The output of the accumulation register 14 is supplied to the D/A converter 15, which outputs the clock signal 1.
After being converted back to an analog quantity by 7, the sampling frequency component is removed by a low-pass filter 22 and the resultant signal is supplied to an output terminal 23. An oscilloscope (not shown) whose input selection is set to "DC" is connected to the output terminal 23.

In the ripple voltage measuring device shown in FIG. 3, when a voltage as shown in FIG. 4a is applied to the input terminal 11, the output of the subtracter 18 becomes as shown in FIG. 4b. In other words, it becomes a digital quantity with a large absolute value in response to a change in DC voltage.

However, for the ripple component, a digital quantity with a small absolute value is obtained. Therefore, the comparator 1 has a threshold value that is approximately the same as the standard value of the ripple voltage.
9, changes in DC voltage can be detected separately.

By generating a clear signal 22 from the comparator 19 to clear the accumulation register 14 when the absolute value of the output of the subtractor 18 exceeds the threshold value, the output of the clearance 14 becomes as shown in FIG. 4c. Changes in DC voltage almost disappear. The reason why the waveform of the ripple voltage in FIG. 4c is different from that in FIG. 4a is that the sampling frequency is lowered for convenience of explanation. In reality, the sampling frequency should be set high enough that the waveform does not change.

〔Effect of the invention〕

As described above, according to the ripple voltage measuring device of the present invention, when measuring a minute ripple voltage superimposed on a DC voltage, it is possible to instantly cut off a DC voltage that is extremely large compared to the ripple voltage to be measured. This allows the display to be displayed on the oscilloscope in an extremely short time. Moreover, this greatly improves the workability in inspecting DC stabilized power supplies, which is extremely effective.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a conventional ripple voltage measuring device.
2a and 2b are diagrams showing the operation of the ripple voltage measuring device of FIG. 1, FIG. 3 is a block diagram showing one embodiment of the ripple voltage measuring device of the present invention, and FIGS. FIG. 4c is a diagram showing the operation of the ripple voltage measuring device of FIG. 3, respectively. 11...Input terminal, 12...A/D converter, 1
3...Memory, 14...Accumulation register, 15...
D/A converter, 16... Clock generator, 18...
...Subtractor, 19...Comparator, 20...Adder, 2
1...Threshold value setter, 22...Clear signal, 23...
...Output terminal.

Claims (1)

[Claims] 1. An analog-to-digital converter that samples an input analog signal at a predetermined sampling period and converts it into a digital signal; and an analog-to-digital converter to which the output digital signal of the analog-to-digital converter is supplied and has a time difference of one sampling period interval. A subtraction means for extracting a difference between output signal digital values, a subtraction output signal of the subtraction means and a reference threshold signal are supplied, and the absolute value of the digital value represented by the subtraction output signal is equal to or less than the threshold represented by the reference threshold signal. a comparison means that outputs a clear signal when the value is greater than a value, and a comparison means that is supplied with the subtracted output signal and the clear signal, accumulates a digital value represented by the subtracted output signal, and adds up the digital value represented by the subtracted output signal each time the clear signal is supplied; , a digital-to-analog converter for converting an output digital signal from the accumulation means into an analog signal, and a filter for removing sampling frequency components from the output signal of the digital-to-analog converter. Voltage measuring device.