JPH0128401Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a multi-point strain measuring device, and more specifically, to an improvement of a multi-point strain measuring device comprising an automatic multi-point switching device and a digital strain measuring device.

In multi-point strain measurements using strain gauges, the specimen to which the strain gauges are attached not only deforms due to loading, but also expands and contracts in a complex and subtle manner due to changes in ambient temperature, and these combine to cause resistance changes in the strain gauges. Therefore, it is necessary to somehow separate the deformation of the specimen due to loading from the deformation of the specimen due to changes in ambient temperature, and measure only the deformation truly caused by the former.

For this reason, conventionally, only when a strain gauge is attached to a specimen with a specific coefficient of linear expansion, the coefficient of linear expansion of the specimen, the coefficient of linear expansion of the resistance wire that makes up the strain gauge, and the temperature coefficient of resistance are They mutually compensate for changes in ambient temperature, and apparently,
Self-temperature compensating strain gauges are used that do not produce an output due to temperature changes.

However, this type of strain gauge can only be applied to a few types of specimen materials, and cannot be applied to specimens made of all materials. , an active gauge that is attached to the specimen and detects deformation due to external force and deformation due to changes in ambient temperature at the same time, and an active gauge that is attached to a dummy piece that is made of the same material and the same heat capacity as the specimen and is in a stress-released state. A temperature compensation method based on the so-called active dummy method is used, which uses a dummy gauge that equivalently detects only the deformation of the specimen due to changes in ambient temperature.

FIG. 1a is a diagram showing an example of a circuit of a conventional common dummy gauge type multi-point switch. In the same figure, fixed resistors R ₁ and R ₂ , a number of active gauges A ₁ to A _o attached to the specimen, and a dummy sheet commonly used for these many active gauges A ₁ to A _o are shown. Gauge D ₁ constitutes Wheatstone Bridge. ,,,...indicate the measurement point number, and when a certain measurement point is selected, one of the corresponding measurement point changeover switches S ₁ , S ₂ , S ₃ , ...S _o
ON, forming one Wheatstone Bridge. At the input end of such a Wheatstone bridge, there is a bridge power supply.
A predetermined bridge voltage is applied from BV.

Currently, there are many active gauges, A ₁ , A ₂ ,
Considering the case where A ₃ and A _o are switched in order and a circuit is inserted on one side of the Wheatstone bridge to measure the strain of the specimen, the active gauges A ₁ , A ₂ , A ₃ , and A _o are as follows: Although the bridge voltage is applied only for a moment when it is selected and measured, the commonly used dummy gauge _D1 , which is fixedly installed on one side of the Wheatstone bridge, applies the voltage at all measurement points after the strain measurement starts. Since the bridge voltage is constantly applied until the strain measurement of This may cause measurement errors. In this case, it is natural to use the dummy gauge in the same way as the active gauge.
If D ₁ , D ₂ , D ₃ , ...D _o are installed at n locations and switched in synchronization with switching of active gauges, zero point fluctuations due to self-heating of strain gauges can be reliably eliminated, but in reality It is not possible to install dummy gauges at each measurement point on the specimen due to structural limitations of the specimen, restrictions on measurement equipment and labor, as well as economic and time constraints. Despite being aware of its shortcomings, the current situation is that the common dummy gauge method is unavoidably used.

Figure 1b is a schematic diagram of the strain gauge shown in Figure 1a connected to the strain gauge connection terminal plate of a multi-point switch. A gauge connection terminal T _A and a dummy gauge connection terminal T _D are provided. Active gauge A ₁ affixed to each measurement point
~ A _o are respectively connected to the corresponding active gauge connection terminal T _A , while the common dummy gauge
D ₁ is connected to measurement points ~ by common lead wires L ₁ and L ₂ .

Figure 2 a and b cover the shortcomings of the active dummy method shown in Figure 1 a and b, and remove the influence of ambient temperature changes to provide accurate strain measurements. This shows a reference example of the temperature compensation method using computer software that was attempted to be implemented. Figure 2a shows a Wheatstone bridge circuit for measuring strain at multiple points.
Parts corresponding to those in FIG. 1a are designated by the same reference numerals. In this reference example, the common dummy gauge D ₁ shown in Figure 1a is replaced with a fixed resistor R ₃ , and measurement points ~ that exhibit the same behavior with respect to ambient temperature changes are grouped together, and this group The measurement point includes n-1 active gauges A ₁ to A _o and a temperature compensation dummy gauge D ₁ (connected to the measurement point) that is commonly used by these active gauges.

In addition, the active gauges A _o+1 , A _o+2 , A _o+3 , etc. after measurement point n+1 shown as a group,
The dummy gauge D ₂ is also grouped based on the same idea as groups, and hereinafter it is assumed that there are a number of such groups.

Fig. 2b is a block diagram of the entire strain measurement system according to the reference example, and the strain gauges shown in groups on the left and the automatic multipoint switch 20 correspond to Fig. 2a. . The digital strain measuring instrument 21 is composed of, for example, an amplifier, an A/D converter, an initial value storage device, an arithmetic circuit, a printer, etc., and is an initial value storage/arithmetic type strain measuring instrument that is normally used for multi-point strain measurement. and its output is the value of the specimen (therefore the strain gauge)
The strain in the specimen caused by loading is expressed by subtracting the value measured when the specimen (therefore, the strain gauge) is in an unloaded state (i.e., the initial value) from the value measured when the specimen is loaded. However, it also includes the apparent strain component due to changes in ambient temperature during measurement.

This output is sent to the computer 2 online via the interface 22 or online using a paper tape punch 23, paper tape 24, etc.
5 is now entered. The computer 25 includes a paper tape reader 26, a typewriter 27,
Peripheral devices such as a magnetic disk 28 and an X-Y plotter 29 are added, making up a strain measurement system as a whole.

In such a system, prior to strain measurement, the grouping of strain gauges under the same temperature condition and the measurement point number to which a common dummy gauge within each group is connected are used as control information.
It is necessary to input the temperature in advance from the typewriter 27 or the paper tape reader 26 to ensure that the temperature compensation is performed by the program without error.

After dividing the input data into groups and distinguishing between active gauges and dummy gauges, the computer 25 calculates the measurements of the dummy gauges included in the group based on the measured values of a large number of active gauges for each group. By subtracting the values, a correct temperature-compensated measurement value (strain amount) is obtained.

Therefore, in this case, both the active gauge and the dummy gauge are scanned with exactly the same operation pattern, so unlike the common dummy gauge type shown in FIG.
Although no measurement errors occur due to self-heating of the strain gauge, there are drawbacks as described in (1) and (2) below.

(1) Disadvantages of the online method (a) Typewriters 27, magnetic disks 28, X-Y plotters 29, etc. cannot be used at outdoor measurement sites where dust is rising, so measurements cannot be performed with such a system.

b) The system is too large to be transported and installed in areas with poor footing, such as construction sites for buildings, bridges, roads, dams, etc.

c Measurement cannot be performed in places with vibration or on a moving object.

d) The operating temperature range is limited to +5 to +35℃ and the humidity is limited to 80% or less depending on the peripheral devices of the computer 25.
−10 is a very normal range for strain measurement.
Measurement becomes impossible at temperatures up to +40°C (sometimes above +40°C) and humidity around 85%.

e The entire system becomes extremely large and expensive.

f In addition to requiring extensive advance preparation for measurement, there is a risk that control information such as grouping of strain gauges and positions of dummy gauges may be input into the computer 25 by mistake due to input errors, communication errors, operational errors, etc. by the measuring staff. There are many cases where this may cause confusion in the measurement results.

(2) Disadvantages of offline method a: The automatic multipoint switch 2 is brought to the measurement site.
0. Only the digital strain measuring device 21 and the paper tape punching device 23 are required, but during measurement, it is not possible to know the temperature-compensated measurement value at each measurement point.

b. Since it takes time to input the outputted paper tape 24 into the computer 25 and obtain the results, the measurement results for one loading condition cannot be used for measurements that determine the next loading condition.

c. Similar to the online method, control information may be input into the computer 25 by mistake, causing confusion in the measurement results.

The present invention was made in view of the drawbacks of the conventional examples and reference examples as described above, and its purpose is to
It is small and inexpensive, and can withstand use in harsh environments such as high or low temperatures, places with vibrations, and places with dust. It is easy to set up measurements, is less likely to cause connection or setting errors, and is less prone to distortion. To provide a multi-point strain measuring device capable of accurately measuring true strain while completely eliminating the influence of self-heating caused by a bridge power source of a gauge and compensating for the influence of ambient temperature changes.

In order to achieve the above object, the present invention uses a multi-point strain measuring device consisting of an automatic multi-point switching device and a digital strain measuring device. 1 for each point installed at the temperature condition measurement point.
A plurality of active gauges forming a group and the above-mentioned 1
A gauge mode setting device that sets the distinction of one dummy gauge provided for each group for each measurement point, and a gauge mode setting device that connects the active gauge and the dummy gauge to their respective input terminals, and connects the active gauge and the dummy gauge to the control signal output from the control circuit. Therefore, an automatic multi-point switch selects the active gauges or the dummy gauges one by one according to a predetermined order and connects them to one side of the Wheatstone bridge, and sequentially sends out the output of the Wheatstone bridge from the output end; A bridge power supply that applies a bridge voltage to the input terminal of the Wheatstone bridge and a gauge mode setting device that corresponds to the gauge selected by the automatic multi-point switch are connected to either the active gauge or the dummy gauge. a determination circuit that determines whether the active gauge is set to 1 and outputs an active gauge determination signal or a dummy gauge determination signal to the control circuit; and a determination circuit that outputs an active gauge determination signal or a dummy gauge determination signal to the control circuit; an A/D converter controlled by the control circuit when the control circuit receives the determination signal and the dummy gauge determination signal;
an initial storage device that temporarily stores initial data ε _IA on the active gauge side and initial data ε _ID on the dummy gauge side obtained through a changeover switch; When the control circuit receives the dummy gauge determination signal from the first changeover switch and the determination circuit, which are separated from the initial value storage device by the A/D converter and the control circuit, which are controlled by the A/D converter and the control circuit. a second changeover switch controlled by this control circuit; and a dummy gauge register that temporarily stores the loading measurement data ε _LD on the dummy gauge side obtained through the second changeover switch, and the state loaded on the specimen. the A/D converter controlled by the control circuit when the control circuit receives an active determination signal;
The initial data ε _IA and ε _ID , which are temporarily stored while receiving the loaded measurement data ε _LA of each active gauge forming one group as described above, obtained through the changeover switches of the Load measurement data ε _LD on the dummy gauge side received from the value storage device and further temporarily stored
an arithmetic circuit that receives the dummy gauge from the dummy gauge register and executes an arithmetic operation according to the following arithmetic expression: ε _T = (ε _LA −ε _IA )−(ε _LD −ε _ID ) to obtain the temperature-compensated true strain ε _T ; , and a display means for displaying the true strain ε _T which is the calculation result of this calculation circuit, and eliminates the influence of self-heating caused by the bridge power supply of the active gauge and the dummy gauge under exactly the same conditions. The present invention is characterized in that it is configured so that expansion and contraction of the specimen due to changes in ambient temperature is corrected, and only the deformation of the specimen caused by loading can be accurately measured.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

Figures 3a and 3b are both related to the present invention, and Figure 3a is a circuit diagram showing the automatic multi-point switch and gauge mode setting device in relation to the strain gauge;
FIG. 1B is a block diagram showing the structure of an embodiment of the entire multi-point strain measuring device.

In Figure 3a, a Wheatstone bridge for performing multi-point strain measurements is connected to fixed resistors R ₁ ,
Similar to R ₂ , R ₃ and FIG. 2a, the grouped active gauges A ₁ to _{A o} , A _o+1 , A _o+2 , A _o+3 ,
...and a dummy gauge included in each group
It is now composed of D ₁ , D ₂ ,... ,,,..., n+1 , n+2 ,
n+3, . . . indicate measurement point numbers, and the automatic multi-point switching device has one measurement point changeover switch S ₁ to S _o , S _o+1 , S _o+ for each of these measurement points. ₂ , So ₊₃ ,
... are provided, and when a selection command signal for selecting a measurement point is input from a control circuit described later, the corresponding measurement point changeover switch S ₁ to S _o , S _o+1 , S _o+2 ,...
One of the Wheatstone bridge circuits is turned on for a certain period of time to form one Wheatstone bridge circuit. On the other hand, in this example, each measurement point,..., n+1, n+2, n+
Gauge mode setting switches K ₁ , K ₂ , as gauge mode setting devices for each of 3,...
K ₃ ,...K _o , K _o+1 , K _o+2 , K _o+3 ,... are provided. This gauge mode setting switch is a switch that sets whether the strain gauge connected to a certain measurement point is used as an active gauge or a dummy gauge. For example, if the dummy gauge is D ₁ , set it to the dummy side by turning (or pushing) the setting switch K ₁ at the measurement point to the "D" side as shown by the arrow in the figure, and vice versa. If the strain gauge affixed to the measurement point is, for example, active gauge _A1 , set it to active by turning (or pushing) setting switch _K2 to the A side as shown by the arrow in the figure. It can be set on the side.

In addition, this example differs from the reference shown in Figure 2a in that the active gauges installed at each of a large number of measurement points are divided into groups to be installed at measurement points with the same temperature conditions. Same as the example, but the positions of the dummy gauges D ₁ and D ₂ are different.
In this embodiment, dummy gauges D ₁ and D ₂ are connected to the first measurement point of each group.

In FIG. 3b, the strain gauges pasted at a large number of measurement points are appropriately divided into groups, groups, etc., and then connected to an automatic multi-point switch 20. In this case, the common dummy gauge D ₁ ,
D ₂ ,... are connected so that they are at the first measurement point,
Along with this, gauge mode setting switches K ₁ , K ₂ ,
K ₃ , K ₄ , ... are set as shown in Figure 3a.

The part surrounded by the one-dot chain line shows the digital strain measuring device 30, which is the main part of the present invention, and the digital strain measuring device with the initial value storage calculation method is connected to the gauge selected by the automatic multi-point switch 20. a determination circuit 31 that determines whether the corresponding gauge mode setter is set to the active gauge or the dummy gauge, and outputs an active gauge determination signal or a dummy gauge determination signal to a control circuit 32 to be described later; Common dummy gauge D ₁ , D ₂ ,
A dummy gauge register 36 that temporarily stores the measured values of... and this dummy gauge register 36
It has an additional input selector switch _SW2 . Specifically, the digital strain measuring instrument 30 using the initial value storage method described above has an automatic multi-point switching point 2.
An amplifier 33 that amplifies minute data outputs from the dummy gauge and active gauge to an appropriate level, which are sequentially output from 0, and when the analog signal output from the amplifier 33 receives a conversion command signal output from the control circuit 32. The A/D converter 34 that converts into a digital signal, the initial value storage device 35 that receives and stores the initial value (or initial data) in a no-load state prior to measurement via switch SW ₁ , and the control circuit 32 are activated. An A/D converter 34 and an input changeover switch are controlled by the control circuit 32 when receiving the chive gauge determination signal.
An arithmetic circuit 37 that receives data from each active side via SW ₂ and the output from the dummy gauge register 36 and performs a predetermined temperature compensation calculation, and a printer as a display means for displaying the calculation results of this arithmetic circuit 37. 38, a bridge power supply 39 that applies a bridge voltage to the Wheatstone bridge, a control circuit that provides control signals to and controls the automatic multi-point switch 20, A/D converter 34, dummy gauge register 36, arithmetic circuit 37, etc. It consists of 32.

Next, the operation of the embodiment shown in FIG. 3b will be explained.

When measuring strain using the multi-point strain measuring device of the present invention, first, as with conventional strain measuring devices using the initial value storage calculation method, when the specimen is in an unloaded state, switch SW ₁ is placed on the side and After the initial value of the strain gauges at all measurement points under no-load condition, that is, the initial value, is stored in the initial value storage device 35, the switch SW ₁ is switched to the control circuit 3.
2 to the (M) side, load the specimen, and measure all points starting from the group again. At this time, the gauge mode setting switch K ₁ ,
The setting status of K ₂ ,... is judged by the judgment circuit 31, and if the output from this judgment circuit 31 is a dummy gauge judgment signal, the control circuit 32 controls the switch.
Set SW ₂ to D side to temporarily store the measured value (measured data when loaded) in the dummy gauge register 36, and if it is an active gauge judgment signal, switch input changeover switch SW ₂ to A, and then The calculation circuit 37 performs the following calculation to determine the temperature-compensated true strain ε _T , and the printer 38 prints and stores it.

ε _T = (ε _LA − ε _IA ) − (ε _LD − ε _ID ) …(1) where, ε _T : Temperature compensated true strain ε _LA : Active gauge measurement when loaded on the specimen Value ε _IA : Measured value of active gauge before loading on the specimen, i.e. initial value of active gauge ε _LD : Measured value of dummy gauge when loaded on specimen ε _ID : Dummy value before loading on specimen The measured value of the gauge, that is, the initial value of the dummy gauge Calculation of the temperature-compensated true strain ε _T using equation (1) above is performed using the dummy gauges D ₁ , D ₂ , etc. located at the beginning of each strain gauge group, respectively. Since the active gauge readings of each group are individually corrected, there is no unnecessary self-heating of the dummy gauge, and there is no need to use a computer.
Ideal temperature compensation can be easily and reliably achieved.

As explained above, unlike conventional devices, the multi-point strain measuring device according to the present invention eliminates compensation errors caused by self-heating of the common dummy gauge, and also uses the temperature compensation method using the computer software shown as the reference example above. Because it has an extremely simple and inexpensive configuration without using a large-scale computer,
It has the following advantages:

Regarding self-heating, the common dummy gauge is measured under the same conditions as the active gauge, so
Unlike the conventional device shown in Figure 1a, it eliminates the compensation error caused by self-heating of the dummy gauge, corrects the expansion and contraction of the specimen due to changes in ambient temperature, and only deforms the specimen caused by loading. It is possible to accurately measure only the strain of

Dummy gauges are used to divide multiple active gauges installed at measurement points under the same temperature conditions into groups, and only one dummy gauge is installed per group. Compared to a configuration in which the switch is configured to switch in synchronization with the switching of the active gage, it is possible to reduce the number of dummy gauges, reduce labor costs, and shorten preparation time. The method can be simplified by a few minutes, and the measurement time can be shortened.

Temperature compensation using a dummy gauge can be performed using only decimal digit integer operations without using a large-scale computer, making the circuit configuration simple.
It is reliable and extremely inexpensive.

Unlike a computer with peripheral devices as shown in the reference example, it should not be used in locations with harsh environmental conditions, such as locations with an ambient temperature of -10 to +50°C, relative humidity of 85% or higher, or outdoors where there is dust. Measurements can be taken in rough locations, construction sites with poor footing, and on moving objects. And, unlike a method using a computer, it does not require a particularly skilled operator.

When a strain gauge is connected to an automatic multi-point switching device, the gauge mode can be set simply by setting the distinction between an active gauge and a dummy gauge in the gauge mode setting device before and after this connection operation. As in the case of using a computer, the combination of the active gauge and dummy gauge may become confused due to input errors by the measuring staff, communication errors, operational errors by the computer operator, etc., and the temperature compensation results may be distorted. There is very little possibility that this will occur, and highly reliable temperature compensation and strain measurement can be performed.

The present invention is not limited to the embodiments described above and shown in the drawings, and modifications can be made within the scope of the invention. For example, the gauge mode setting device is shown in FIG. As shown in the figure, the same switch is not only used to set active gauges and dummy gauges, but also has the function of specifying the number of strain gauges included in the Wheatstone bridge to 1, 2, 4, etc. It is also possible to make settings possible.

In addition, in the above explanation, the position of the dummy gauge was set as the first measurement point of each strain gauge group, but if an active gauge register that temporarily stores the measured load value is added to the specimen, the strain gauge No matter which measurement point in the group the dummy gauge is present, temperature compensation can be performed correctly in the same way as described above. In this case, the automatic multi-point switch 20
selects the output of the active gauge, and at the same time, when the control circuit 32 receives an active gauge determination signal from the gauge mode setter corresponding to the gauge selected by the automatic multi-point switch 20, this The input changeover switch _SW2 controlled by the control circuit 32 is connected to the active gauge register side, and the output of the A/D converter 34 is configured to be supplied to this active gauge register. Bye. The calculation operation by the calculation circuit 37 may be performed each time the measurement operation of each strain gauge group is completed, or may be performed at once after the measurement operation of all groups is completed.

[Brief explanation of the drawing]

Figures 1a and b are diagrams showing a circuit example of a conventional common dummy gauge multipoint switch and the connection status of strain gauges to the multipoint switch, respectively, and Figures 2a and b
is an explanatory diagram showing a reference example of a temperature compensation method using computer software, which the present applicant has attempted to implement privately; part a is a diagram showing a circuit example of an automatic multipoint switch; b is a block diagram of the entire measurement system;
Figures 3a and 3b show the configuration of an embodiment of the multipoint strain measuring device according to the present invention, and part a shows the relationship between the automatic multipoint switch and the gauge mode setting device with respect to the strain gauge. FIG. 4 is a schematic diagram showing an example of a setting switch as a gauge mode setting device used in the device of the present invention. ,,..., n+1 , n+2 , n+3
, n+4...Measurement point number, K ₁ , K ₂ ,...K _o ,
K _o+1 , K _o+2 , K _o+3 , K _o+4 ... Gauge mode setting switch, T _A ... Active gauge connection terminal,
T _D ……Dummy gauge connection terminal, A ₁ , A ₂ ,…,
A _o , A _o+1 , A _o+2 , A _o+3 ...active gauge,
D ₁ , D ₂ ,..., D _o ...Dummy gauge, S ₁ , S ₂ ,...,
S _o ...Measuring point changeover switch, _R1 , _R2 , _R3 ...Fixed resistance, BV...Bridge power supply, 30...Digital strain measuring instrument, 31...Judgment circuit, 32...
Control circuit, 33...Amplifier, 34...A/D converter, 35...Initial value storage device, 36...Dummy gauge register, 37...Arithmetic circuit, 38...Printer, 39...Bridge power supply.

Claims (1)

[Scope of Claim for Utility Model Registration] In a multi-point strain measuring device consisting of an automatic multi-point switching device and a digital strain measuring device, measurement of the same temperature conditions among active gauges provided at each of a large number of measurement points on a specimen. a gauge mode setting device for setting, for each measurement point, a distinction between a plurality of active gauges forming one group for each point and a dummy gauge provided for each group; Dummy gauges are respectively connected to the input terminals, and the active gauges or the dummy gauges are selected one by one according to a predetermined order by a control signal output from the control circuit, and connected to one side of the Wheatstone bridge. an automatic multi-point switch that sequentially sends out the output of the Wheatstone bridge from the output terminal; a bridge power supply that applies a bridge voltage to the input terminal of the Wheatstone bridge; and a gauge selected by the automatic multi-point switch. a determination circuit that determines whether a corresponding gauge mode setting device is set to the active gauge or the dummy gauge, and outputs an active gauge determination signal or a dummy gauge determination signal to the control circuit; When the control circuit receives an active gauge determination signal and a dummy gauge determination signal from the determination circuit in an unloaded state before loading the specimen, the A/D converter and the an initial value storage device that temporarily stores initial data ε _IA on the active gauge side and initial data ε _ID on the dummy gauge side obtained through the changeover switch 1; The control circuit receives the dummy gauge determination signal from the first changeover switch and the determination circuit, which are separated from the initial value storage device by the A/D converter controlled by the circuit and the control circuit. a second changeover switch controlled by this control circuit, and a dummy gauge register that temporarily stores the loading measurement data ε _LD on the dummy gauge side; In this state, when the control circuit receives an active determination signal, one group is obtained via the A/D converter controlled by the control circuit and the first and second changeover switches, respectively. The initial data ε _IA and ε _ID are temporarily stored while receiving the loaded measurement data ε _LA on each active gauge side.
is received from the initial value storage device, and the temporarily stored loading measurement data ε _LD on the dummy gauge side is received from the dummy gauge register, and ε _T = (ε _LA −ε _IA )−(ε It is equipped with an arithmetic circuit that performs an arithmetic operation using the arithmetic formula _LD −ε _ID ) to obtain a temperature-compensated true strain ε _T , and a display means that displays the true strain ε _T that is the arithmetic result of this arithmetic circuit. , while eliminating the influence of self-heating caused by the bridge power supply of the active gauge and dummy gauge under exactly the same conditions, the expansion and contraction of the specimen due to changes in ambient temperature is corrected, and the deformation of the specimen caused by loading is corrected. A multi-point strain measuring device characterized in that it is configured to be able to accurately measure only.