JP2001133489A - Rms-measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an RMS-measuring device for adjusting zero point by directly measuring the output offset eo(rms) of an RMStoDC converter without using any reference voltages. SOLUTION: The RMS-measuring device is provided with a first switch circuit for selectively outputting an input signal and a zero-potential signal, a variable DC signal generator for generating an arbitrary DC signal, an adder for outputting the addition signal of the output of the first switch circuit and that of the variable DC signal generator, a preamplifier for inputting the output of the adder, an RMStoDC converter for inputting the output of the preamplifier and then outputting a signal corresponding to the RMS value of the input signal, a second switch circuit for selectively outputting the output of the preamplifier and that of the RMStoDC converter, a measurement circuit that is connected to the output of the second switch circuit, and at least a control circuit for controlling the first switch circuit, the second switch circuit, and the variable DC signal generator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an RMS (effective value)
The present invention relates to an improvement of a zero adjustment circuit of a measuring device.

[0002]

2. Description of the Related Art A conventional RMS measuring apparatus will be described with reference to FIG. In the figure, an input terminal 11 is connected to a movable contact a of a switch circuit 14, a reference voltage 12 is connected to a movable contact b of the switch circuit 14, and a reference voltage 13 is connected to a movable contact c of the switch circuit 14. .

The fixed contact d of the switch circuit 14 is connected to the input of a preamplifier 15, and the output of the preamplifier 15 is RM
Connected to the input of StoDC converter 16 and RMSt
The output of the oDC converter 16 is connected to the input of the measurement circuit 17.

The control circuit 18 controls the entire RMS measuring apparatus 10, performs arithmetic processing on the measured values measured by the measuring circuit 17, displays the RMS value of the input signal Sin on the display means 19, The switching of the switch circuit 14 is performed in response to the above.

When measuring the RMS value of the input signal Sin in the RMS measuring apparatus 10 having such a configuration, first, the control circuit 18 switches the switch circuit 14 to the movable contact a side.

As a result, the input signal Sin is input to the preamplifier 15, where it is amplified to a predetermined amplitude.
It is sent to the RM to DC converter 16.

The amplified signal of the input signal Sin input to the RM to DC converter 16 is input signal Sin
After being converted to a DC voltage corresponding to the RMS value of

The DC voltage input to the measuring circuit 17 is subjected to appropriate numerical processing by the control circuit 18 and then displayed on the display means 19 as the RMS value of the input signal Sin.

Further, the RMS measuring apparatus 1 having such a configuration
The procedure for performing zero adjustment at 0 will be described below.

Generally, an RMS measuring apparatus having such a configuration is used.
Of the RM to DC converter 16 used in the device 10
The output characteristics are as follows: Vo = √ (ei^Two+ En^Two+ Eo^Two) + Eo_(rms) (1) is represented by Here, Vo is the RM to DC converter
The output signal of the data 16, ei is the input signal, en is the input noise
, Eo is the residual offset of the preamplifier 15, eo
_(rms)Is the output offset of the RM to DC converter
is there.

Accordingly, the RMS measurement apparatus 10 having such a configuration, first determine the RMStoDC converter output offset eo _(rms), then the output offset eo from the measured values obtained by the measurement circuit 17 _(rms) By performing the subtraction, the zero point can be adjusted.

In order to obtain the output offset eo _(rms) , a method of inputting a zero signal to the input terminal 11 and measuring the measured value at this time by the measuring circuit 17 can be considered. As is apparent, RMToDC
The input / output characteristics of the converter cause an error Eer near the zero point as shown in FIG. 5 due to the influence of input noise en generated at the previous stage of the RMToDC converter and the residual offset eo of the preamplifier. Thus, the output offset eo _(rms) cannot be accurately obtained by the method of simply measuring and obtaining the zero signal.

Therefore, in the conventional RMS measuring apparatus 10,
In order to accurately obtain the output offset eo _(rms) , two reference voltages 12 and 13 are prepared, and the two reference voltages 1 and 13 are prepared.
2 and 13 are input to the amplifier 15 and the measured value V12,
V13 was obtained, and the output offset eo _(rms) was obtained from the intersection of the characteristic approximation straight line L passing through these two points and the vertical axis.

[0014]

However, the conventional R
In the MS measuring device, it is necessary to obtain the characteristic approximation straight line L using two reference voltages in order to obtain the output offset eo _{(rms) (} to perform the zero point adjustment). There is a problem that the load is increased.

An object of the present invention is to provide an RMS measuring apparatus capable of performing zero point adjustment by directly measuring an output offset eo _{(rms) of an} RM to DC converter without using a reference voltage. With the goal.

[0016]

In order to achieve the above object, according to the first aspect of the present invention, a first switch circuit for selectively outputting an input signal and a zero potential signal and an arbitrary DC signal are generated. A variable DC signal generator, an adder that outputs an addition signal of an output of the first switch circuit and an output of the variable DC signal generator, a preamplifier that receives an output of the adder, RMTo which receives the output of the operational amplifier and outputs a signal corresponding to the RMS value of the input signal
A DC converter, the output of the preamplifier and the RMS
a second switch circuit for selectively outputting the output of the toDC converter, a measurement circuit connected to the output of the second switch circuit, at least the first switch circuit, the second switch circuit, and the variable DC A control circuit for controlling the signal generator is provided.

Further, in the invention described in claim 2, the preamplifier includes a band limiting filter.

According to such a configuration, by the switching operation of the first switch circuit and the second switch circuit, the preamplifier of the preamplifier to which the added signal of the zero potential signal and the output signal of the variable DC signal generator is inputted is input. The output can be measured directly by a measuring circuit. In such a state, the band is limited by the filter function of the preamplifier, so that R
The input noise en of the signal input to the MstoDC converter can be extremely reduced. Also, at this time,
By adjusting the output of the variable DC signal generator so that the output of the measurement circuit indicates zero, the residual offset of the signal input to the RMToDC converter can be removed. The output of the preamplifier adjusted in this way is input to the RM to DC converter, and the RMS
By measuring the output of the toDC converter, the RM
The output offset eo _(rms) of the StoDC converter can be directly measured by the measurement circuit.

According to the third aspect of the present invention, a VGA circuit for normalizing an input signal to a constant value, a variable DC signal generator for generating an arbitrary DC signal, an output of the VGA circuit and the variable DC signal generation Adder that outputs an addition signal of the output of the adder, a preamplifier that receives the output of the adder, and an RM to DC converter that receives the output of the preamplifier and outputs a signal corresponding to the RMS value of the input signal A second switch circuit for selectively outputting an output of the preamplifier and an output of the RMToDC converter, a measurement circuit connected to an output of the second switch circuit, and at least the second switch circuit. A control circuit for controlling the VGA circuit is provided.

According to a fourth aspect of the present invention, the preamplifier includes a band limiting filter.

According to a fifth aspect of the present invention, the variable DC signal generator is realized by a D / A converter connected to the control circuit. The measurement circuit is realized by an A / D converter connected to the control circuit.

According to such a configuration, the VGA circuit (Variable Gain) is switched by the switching operation of the second switch circuit.
Amp), the output of the preamplifier to which the added signal of the input signal normalized to a constant value and the output signal of the D / A converter is input can be directly measured by the A / D converter. In such a state, the band is limited by the filter function of the filter circuit, whereby
The input noise en of the signal input to the DC converter can be extremely reduced. At this time, by adjusting the output of the D / A converter so that the output of the measurement circuit indicates zero, the residual offset of the signal input to the RM to DC converter can be removed. The output of the preamplifier adjusted in this manner is set to RMToD
By inputting to the C converter and measuring the output of the RM to DC converter at this time, the output offset eo _(rms) of the RM to DC converter can be directly measured by the measurement circuit.

Further, according to this configuration, the signal bypassing the RM to DC converter can be directly measured by the A / D converter by the switching operation of the second switch circuit, and the second terminal of the adder can be measured. It is possible to set a signal to be input to the switch and read the output of the second switch circuit by a digital signal.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a circuit diagram showing one embodiment of the RMS measuring apparatus according to the present invention. In the figure, the same components as those of the conventional example are denoted by the same reference numerals, and description thereof will be omitted.

In FIG. 1, the input terminal 11 is connected to the movable contact a of the switch circuit 21 and the common potential is connected to the movable contact b of the switch circuit 21.

The fixed contact d of the switch circuit 21 is connected to the first input terminal of the adder 22, the output of the variable DC signal generator 25 is connected to the second terminal of the adder 22, The output terminal is connected to the input of the preamplifier 15. The preamplifier 15 used here has a filter function, and can output the input signal after limiting the band.

The output of the preamplifier 15 is connected to the input of the RM to DC converter 16 and the switch circuit 2
The output of the RM to DC converter 16 is connected to the movable contact b of the switch circuit 21, and the fixed contact d of the switch circuit 21 is connected to the input of the measurement circuit 17.

The control circuit 24 controls the entire RMS measuring device 20. The control circuit 24 performs an arithmetic operation on the measured value measured by the measuring circuit 17 to display the RMS value of the input signal Sin on the display means 19, The switching of the switch circuits 21 and 23 is performed in accordance with the above.

When measuring the RMS value of the input signal Sin in the RMS measuring apparatus 20 having such a configuration, first, the control circuit 24 switches the switch circuit 21 to the movable contact a side, and switches the switch circuit 23 to the movable contact b. Switch to side.

As a result, the input signal Sin is input to the preamplifier 15, where it is amplified to a predetermined amplitude.
It is sent to the RM to DC converter 16.

The amplified signal of the input signal Sin input to the RM to DC converter 16 is the input signal Sin
After being converted to a DC voltage corresponding to the RMS value of

The DC voltage input to the measuring circuit 17 is displayed on the display means 19 as the RMS value of the input signal Sin after appropriate numerical processing is performed by the control circuit 24.

Further, the RMS measuring apparatus 2 having such a configuration
FIG. 2 shows a procedure for performing zero adjustment at 0.
This will be described below using the flowchart shown in FIG.

The filter function of the preamplifier 15 is turned on,
Apply bandwidth restrictions. (ST1)

The switch circuit 21 is switched to the movable contact b side, and the switch circuit 23 is switched to the movable contact a side. (S
T2)

The output of the variable DC signal generator 25 is adjusted so that the output of the measuring circuit 17 indicates zero. (ST3)

The switch circuit 23 is switched to the movable contact b side, and the output signal of the RM to DC converter 16 is measured by the measuring circuit 17. At this time, the input noise en of the signal input to the RMToDC converter 16 is ST ST
At the time point 1, since the band is limited to the preamplifier 15, the size is extremely small. Also, RMToDC
Since the residual offset noise eo of the signal input to the converter 16 is set to zero by adjusting the output of the variable DC signal generator 25 at the time of ST2, the output of the RM to DC converter 16 at this time is (RMSt)
If the internal noise of the oDC converter 16 is small enough, it will be the output offset eo _{(rms) of the} pure RMStDC converter. (ST4)

Zero point adjustment is performed using the output offset eo _(rms) of the RM to DC converter obtained in ST4. (ST5)

The switch circuit 21 is switched to the movable contact a side, and the switch circuit 23 is switched to the movable contact b side. At this time, a reference voltage Vref whose voltage has been accurately determined in advance is applied to the input terminal 11, and the measuring circuit 1 is set so that a value corresponding to the reference voltage Vref is measured by the measuring circuit 17.
7 may be adjusted to adjust the span. (S
T6)

The filter function of the preamplifier 15 is turned off,
Release the band limitation and end the zero point adjustment. (ST
7)

In the RMS measuring apparatus of the present invention, zero point adjustment can be performed by directly measuring the output offset eo _{(rms) of the} RM to DC converter without using a reference voltage by such an operation.

It should be noted that the foregoing description has been directed to specific preferred embodiments for the purpose of illustration and illustration of the invention. Therefore, the present invention is not limited to the above-described embodiments, and includes many more modifications without departing from the spirit thereof.
This includes deformation.

For example, as shown in FIG.
The VGA 31, the adder 22, and the filter circuit 33 are connected in series between the MS to DC converter 16, and the RM to D
The output of the fixed contact d of the switch circuit 23 for selectively outputting the output of the C converter 16 and the filter circuit 33 is input to the A / D converter 34, and the output of the D / A converter 35 is input to the second input terminal of the adder 22. The same effect as that of the RMS measuring device shown in FIG.

In the RMS measuring device 30 having such a configuration,
After normalizing the input signal Sin to a constant value by the VGA 31, it is possible to obtain the RMS value of the input signal Sin by the RM to DC converter 16. Further, by switching the switch circuit 23 to the movable contact a side, a signal bypassing the RM to DC converter 16 can be directly measured. Further, reading of measured values and setting of a signal to be input to the second terminal of the adder 22 can be processed by a digital signal.

[0045]

As is apparent from the above description,
According to the present invention, the following effects can be obtained. According to the first and second aspects of the present invention, the output offset eo _(rms) of the RM to DC converter, which has conventionally been obtained using two reference voltages and a characteristic approximation line obtained by measuring these reference voltages, is directly calculated. Since it is possible to perform zero adjustment by measuring, the accuracy of zero adjustment is improved,
Since it is possible to reduce the calculation load of the two reference voltages and the control circuit, it is possible to realize a significant cost reduction of the entire apparatus.

According to the third to sixth aspects of the present invention, the above-mentioned effect is realized, and the zero point can be directly adjusted by a digital signal. Therefore, it is possible to flexibly cope with applications such as remote zero point adjustment. It becomes possible.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of an RMS measurement apparatus according to the present invention.

FIG. 2 is a flowchart illustrating a zero point adjustment procedure of the RMS measuring apparatus according to the present invention.

FIG. 3 is a configuration diagram showing one embodiment of an RMS measuring apparatus according to the present invention.

FIG. 4 is a configuration diagram illustrating an example of a conventional RMS measurement device.

FIG. 5 is a diagram illustrating a method of adjusting a zero point of a conventional RMS measuring apparatus.

[Explanation of symbols]

 10, 20, 30 RMS measuring device 11 Input terminal 12, 13 Reference voltage 14, 21, 23 Switch circuit 15 Preamplifier 16 RMToDC converter 17 Measurement circuit 18, 24, 36 Control circuit 19 Display means 22 Adder 31 VGA 33 Filter Circuit 34 A / D converter 35 D / A converter

Claims (6)

[Claims] A first switch circuit for selectively outputting an input signal and a zero potential signal; a variable DC signal generator for generating an arbitrary DC signal; an output of the first switch circuit and the variable DC signal generation An adder that outputs an addition signal of the output of the adder; a preamplifier that receives an output of the adder; an RM to DC converter that receives an output of the preamplifier and outputs a signal corresponding to an RMS value of the input signal A second switch circuit for selectively outputting an output of the preamplifier and an output of the RMToDC converter; a measuring circuit connected to an output of the second switch circuit; and at least the first switch circuit. An RMS measuring apparatus comprising: the second switch circuit; and a control circuit for controlling the variable DC signal generator. 2. The RMS measuring apparatus according to claim 1, wherein said preamplifier includes a band limiting filter. 3. A VGA circuit for normalizing an input signal to a constant value, a variable DC signal generator for generating an arbitrary DC signal, and an addition signal of an output of the VGA circuit and an output of the variable DC signal generator. An adder for outputting, a preamplifier for receiving an output of the adder, an RM to DC converter for receiving an output of the preamplifier and outputting a signal corresponding to an RMS value of the input signal; A second switch circuit for selectively outputting an output and an output of the RM to DC converter; a measurement circuit connected to an output of the second switch circuit; and control for controlling at least the second switch circuit and the VGA circuit. RMS measuring device comprising a circuit 4. The RMS measuring apparatus according to claim 3, wherein said preamplifier includes a band limiting filter. 5. The RMS measuring apparatus according to claim 3, wherein said variable DC signal generator is realized by a D / A converter connected to said control circuit. 6. The RMS measuring apparatus according to claim 3, wherein said measuring circuit is realized by an A / D converter connected to said control circuit.