JPH0810181B2 - Wideband instrumentation amplifier in material testing machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a broadband measuring amplifier in a material testing machine,
In particular, the present invention relates to a technique for widening a frequency band so that a minute signal including a direct current component obtained from a strain gauge or the like can be favorably amplified.

B. Prior Art The conventional measurement amplifier in the material testing machine is configured by using either a DC amplifier or a modulation / demodulation AC amplifier.

C. Problems to be Solved by the Invention However, each method has the following problems.

Problems of noise level and frequency band in DC amplification system There is a mutually contradictory problem that if the noise level is suppressed, the frequency band cannot be widened, and conversely, if the frequency band is widened, the noise level rises. Since there is a strong demand for widening the frequency band in the material testing machine, the frequency band will eventually be widened, but problems remain in the noise level and drift characteristics.

Problems of modulation frequency and frequency band in AC amplification method Since an AC signal, that is, a carrier wave is used for modulation, the frequency component higher than the frequency of the carrier wave cannot be amplified. That is, although the noise level and the drift characteristic are good, the frequency band cannot be widened.

The present invention has been made in view of the above circumstances, and an object thereof is to enable a minute signal including a DC component to be amplified over a wide frequency band in a state of low noise and load lift.

D. Means for Solving Problems The present invention has the following configuration in order to achieve such an object.

That is, the wide band measurement amplifier in the material testing machine of the present invention comprises a DC amplifier connected to the input terminal of a minute signal, a low-pass filter connected to the next stage of the DC amplifier, and an AC amplifier connected to the input terminal. And a high-pass filter connected to the next stage of this AC amplifier, and an adder for adding the output signal from the low-pass filter and the output signal from the high-pass filter, and the DC amplifier and the AC amplifier are the same. The low-pass filter and the high-pass filter are configured to have gain, and the frequency characteristics of the output signals of the both have the same attenuation slope, and are configured to cross over at the same cutoff frequency. It is characterized by.

E. Operation The operation of the configuration of this invention is as follows.

The minute signal from the input terminal is DC-amplified by the DC amplifier, the high-frequency noise is removed by the low-pass filter, and only the DC component is output to the adder. On the other hand, the minute signal from the input terminal is AC-amplified by the AC amplifier, the DC drift component is removed by the high-pass filter, and only the AC component is output to the adder. Then, the DC component and the AC component are added in an analog manner in the adder.

In this case, the DC amplifier and the AC amplifier have the same gain, and the slope in the frequency characteristic of the low-pass filter and the slope in the frequency characteristic of the high-pass filter have the same attenuation slope and cross at the same cutoff frequency. Because it is configured to exceed,
By adding the output signal of the low-pass filter and the output signal of the high-pass filter, an output signal with a flat gain over a wide frequency band can be obtained.

F. Embodiment Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 4 is a schematic configuration diagram showing a mechanical system and an electrical system of a material testing machine when the wide band measurement amplifier according to one embodiment of the present invention is applied to amplification of a load detection unit.

In FIG. 4, 1 is a tester body, 2 is a tester body 1.
A servomotor 3 built in, a deceleration mechanism 3 interlocked with the servomotor 2, 4 a pillar standing upright from the tester body 1, 5 a fixed crosshead installed between the upper ends of both pillars 4, Reference numeral 6 denotes a screw rod vertically installed between the tester main body 1 and the fixed crosshead 5 and interlockingly connected to the reduction mechanism 3, and 7 denotes a movable crosshead screwed to both the screw rods 6.

Reference numeral 8a denotes an upper chuck attached to the fixed crosshead 5, and 8b denotes a lower chuck attached to the movable crosshead 7, which constitutes a chuck mechanism 8 that holds both ends of the test piece M by the upper and lower chucks 8a and 8b.

The fixed crosshead 5 is provided with a load detection unit 9 such as a load cell for detecting the load applied to the test piece M via the upper chuck 8a and converting the load into an electric quantity.

In addition, the servo motor 2, the reduction mechanism 3, the fixed crosshead 5,
The screw rod 6 and the movable crosshead 7 constitute a load mechanism 10 that applies a load to the test piece M.

A is a wide-band measurement amplifier applied as a load amplifier, and is configured so that a positive voltage is output when the load applied to the test piece M is a tensile load, and a negative voltage is output when the load is a compressive load. This wide band measurement amplifier A
The specific configuration of will be described later.

Reference numeral 11 is a controller that controls the servo motor 2 under desired conditions, and 12 is a motor drive circuit (servo amplifier) that directly controls the drive control of the servo motor 2.

From the UP terminal of the controller 11, an up signal for rotating the servo motor 2 in the direction of raising the movable crosshead 7 is output to the U terminal of the motor drive circuit 12, and from the DOWN terminal, the servo is driven in the direction of lowering the movable crosshead 7. A down signal for rotating the motor 2 is output to the D terminal of the motor drive circuit 12, and a clock signal for instructing the rotation speed of the servo motor 2 is output from the CLOCK terminal to the motor drive circuit.
It is configured to be output to 12 C terminals.

The output signal of the wideband measurement amplifier A is the controller
It is fed back to 11 and transmitted to a recorder (not shown).

A specific circuit configuration of the wideband measurement amplifier A is shown in FIG.

In FIG. 1, IN is an input terminal for inputting a minute signal from the load detection unit 9, and the input terminal of the DC amplifier 21 and the input terminal of the AC amplifier 22 are commonly connected to this input terminal IN. . The gain of the DC amplifier 21 and the gain of the AC amplifier 22 are configured to be equal to each other.

Next to the DC amplifier 21, a low-pass filter with a primary characteristic is provided.
23 is connected, and a high-pass filter 24 having a primary characteristic is connected to the next stage of the AC amplifier 22.

The frequency characteristic of the output signal Sa of the low-pass filter 23 and the frequency characteristic of the output signal Sb of the high-pass filter 24, and the same cut-off frequency f _{0 of} both, are configured to have a relationship as shown in FIG. ing.

That is, the attenuation slope of the slope a ₁ of the characteristic curve a of the output signal Sa of the low pass filter 23 and the attenuation slope of the slope b ₁ of the characteristic curve b of the output signal Sb of the high pass filter 24 are configured to be equal to each other. There is. Further, both slopes a ₁ and b ₁ are configured to cross over at the same cutoff frequency f ₀ .

The output terminal of the low-pass filter 23 and the output terminal of the high-pass filter 24 are both 2 of the analog adder 25.
It is connected to the input terminal, and the output terminal of the adder 25 is the output terminal OUT of the wideband measurement amplifier A.

 Next, the operation of this embodiment will be described.

First, the operation of the material test will be described. Both ends of the test piece M are gripped by the upper chuck 8a and the lower chuck 8b. When performing the compression test, various data relating to the compression test is input to the controller 11 from a keyboard (not shown). The main ones are the rotation direction and the rotation speed of the servo motor 2.

By turning on the start switch, the controller
An up signal and a clock signal are output from 11 to the servo motor 2 via the motor drive circuit 12. The up signal determines the rotation direction of the servo motor 2 in the forward rotation direction, and the frequency of the cross signal determines the rotation speed of the servo motor 2. When the servomotor 2 rotates in the normal direction, both screw rods 6 rotate clockwise through the speed reduction mechanism 3,
The movable crosshead 7 rises and applies a compressive load to the test piece M.

On the contrary, when performing the tension test, the controller 11 outputs the down signal and the clock signal to the servo motor 2. Since the servo motor 2 rotates in the reverse direction and the screw rods 6 rotate counterclockwise via the speed reduction mechanism 3, the movable crosshead 7 descends and applies a tensile load to the test piece M.

The compressive load or the tensile load is detected by the load detection unit 9 and is fed back to the controller 11 via the wide band measurement amplifier A, and the driving of the servo motor 2 is continued according to the deviation between the control amount and the target value. The servo motor 2 is stopped when the deviation becomes zero.

The load detection signal input from the load detection unit 9 to the input terminal IN of the broadband measurement amplifier A is a minute voltage (for example, 10 mV). This minute voltage signal is applied to the DC amplifier 21 and the AC amplifier 22.
Entered in and.

The minute signal input to the DC amplifier 21 is DC amplified,
High-frequency noise is removed by the low-pass filter 23,
Only the DC component is output to the adder 25.

The minute signal input to the AC amplifier 22 is AC-amplified, the DC drift component is removed by the high-pass filter 24, and only the AC component is output to the adder 25.

In the adder 25, the DC component from the low pass filter 23 and the AC component from the high pass filter 24 are added.

Frequency characteristic curve a of the output signal Sa of the low-pass filter 23
And the frequency characteristic curve b of the output signal Sb of the high pass filter 24
Since the relationship with is as shown in Fig. 2,
The characteristic curve c of the output signal Sc from the adder 25 is such that the slopes a ₁ and b ₁ are flattened as shown in FIG. 3 and the gain is flat over a wide frequency band from direct current to high frequency range. You get Sc.

Therefore, the DC amplifier 21 only needs to emphasize load lift characteristics, and does not need to have a wide frequency characteristic. Also, as the AC amplifier 22,
Anything that emphasizes low noise and wide frequency characteristics is not required, and load lift characteristics are not required.

Although the low-pass filter 23 and the high-pass filter 24 are configured by primary filters in the above embodiment, higher-order filters may be used. However, in that case, adder
It is necessary to set the circuit constants so that the frequency characteristics become flat over a wide band when synthesized with 25.

In the above embodiment, the load signal from the load detection unit 9 is described as an example of the minute signal processed by the wide band measurement amplifier A, but the present invention is not limited to this, and the extension signal
It goes without saying that the wideband measurement amplifier A may be applied as a device for processing minute signals such as distortion, displacement and the like.

G. Effects of the Invention According to this invention, the following effects are exhibited.

That is, high-frequency noise can be removed by passing the DC-amplified signal through a low-pass filter, while DC drift components can be removed by passing the AC-amplified signal through a high-pass filter. In addition, since the DC component after noise removal and the AC component after drift component removal are added, even if a minute signal containing a DC component is input, the gain is flat over a wide frequency band in the state of low noise and load lift. It is possible to obtain various output signals.

[Brief description of drawings]

1 to 4 relate to an embodiment of the present invention.
FIG. 4 is a block circuit diagram showing a wideband measurement amplifier, FIG. 2 is a frequency characteristic diagram of output signals of a low-pass filter and a high-pass filter, FIG. 3 is a frequency characteristic diagram of an addition signal, and FIG.
The figure is a schematic configuration diagram showing a mechanical system and an electrical system of a material testing machine when a wide band measurement amplifier is applied to amplification of a load detection unit. A: Wide band measurement amplifier IN: Input terminal OUT: Output terminal 21: DC amplifier 22: AC amplifier 23: Low pass filter 24: High pass filter 25: Adder f ₀ ... Cutoff frequency Sa ... … Low-pass filter output signal a …… Output signal Sa characteristic curve a ₁ …… Output signal a slope Sb …… High-pass filter output signal b …… Output signal Sb characteristic curve b ₁ …… Output signal b slope Sc …… Broadband measurement amplifier output signal c …… Output signal Sc characteristic curve

Claims (1)

[Claims] 1. A DC amplifier connected to an input terminal of a minute signal, a low-pass filter connected to the next stage of the DC amplifier, an AC amplifier connected to the input terminal, and a next stage of the AC amplifier. A connected high-pass filter, and an adder for adding an output signal from the low-pass filter and an output signal from the high-pass filter, wherein the DC amplifier and the AC amplifier are configured to have the same gain, What is a low pass filter and a high pass filter?
The frequency characteristics of both output signals have the same attenuation slope,
A wideband instrumentation amplifier in a material testing machine, which is configured to cross over at the same cutoff frequency.