JPH02310402A - Self-diagnosing circuit - Google Patents

Abstract

PURPOSE:To improve the reliability of the results of diagnosis by connecting the output terminal of a bridge circuit including strain gages to the input terminal of a high input resistance differential amplifier circuit and grounding the other inversion input terminal by a resistor having the same resistance as a resistor. CONSTITUTION:Switches SWS3, S4, S6 are turned on and SWS1, S2, S5, S7 are turned off by the signals from an SW control circuit 43 at the time of, for example, a self- diagnosis mode. The connection between the bridge circuit 1 and operational amplifier circuits 10, 14 is interrupted and the non-inversion input terminals of the amplifiers 10, 14 are shorted so that the outputs of the amplifiers 10, 14 do not depend on the output voltage of the circuit 1 any longer. The reference signal from a reference voltage generating circuit 10 is inputted in this state via SWS6 and the resistor 16 to the inversion input terminal of the amplifier 14 and is inputted via a temp. sensitive resistance element 18 to the inversion input terminal of the amplifier 10. The signal corresponding to the reference weight is inputted to the amplifier 14. The outputs from the amplifiers 10, 14 are inputted via the resistors 30, 32 to the differential amplifier circuit 32 and the output signal of the circuit 32 is inputted to a signal processing circuit of a post stage and is displayed as a weight on a display device.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an amplifier circuit, a level conversion circuit, a filter circuit, and an analog-to-digital conversion circuit for processing signals from strain gauges in weight measuring equipment such as electronic scales. This invention relates to a self-diagnosis circuit that checks the operation of circuits, etc.

(Prior art #T) A weight measuring device such as an electronic scale has a plurality of strain gauges (usually four) attached to the surface of a strain body that converts weight I into mechanical strain, and a bridge circuit containing these strain gauges. an amplifier circuit, a level conversion circuit, which connects the signal from this bridge circuit to the subsequent stage.
The signal is configured to be converted into a digital signal suitable for output devices such as display and printing using a filter circuit, an analog-digital conversion circuit, and the like.

Therefore, it is possible to achieve the objective by making sure that all of the many circuits that exist in the path from the strain gauge to the output device are operating normally, so each circuit must be operating normally before the weighing operation. It is necessary to confirm that. For this reason, the operating state of the signal processing circuit is checked by inputting a voltage equivalent to the reference load to the amplification means that receives the output from the bridge circuit, but this check is performed without placing the object on the weighing pan. Since this can only be done on a weighing pan, if a tare bag or the like is piled up on the weighing pan, the operating state cannot be diagnosed, resulting in a problem of reduced reliability.

The present invention has been made in view of these problems, and its purpose is to provide a self-diagnostic device that can diagnose the operating state of a signal detection circuit at any time regardless of whether the weighing pan is loaded or not. The purpose is to provide a diagnostic circuit.

(Means for Solving the Problems) In order to solve such problems, in the present invention, the output terminals of the bridge circuit including strain gauges are respectively connected to the input terminals of the high input resistance differential amplifier circuit via switch means. The output terminal of a voltage generation circuit that outputs a reference voltage is connected to the inverting input terminal of the one high input resistance differential amplifier circuit through a resistor, and The inverting input terminal was grounded by a resistor having the same resistance as the above resistor.

(Function) Even in a loaded state, signal input from the bridge circuit can be cut off by operating the switch, allowing drift detection and self-diagnosis of signal processing circuits including high input resistance differential amplifiers. .

(Example) The details of the present invention will be described below based on illustrated examples.

FIG. 1 shows an embodiment of the present invention, in which reference numeral 1 is a bridge circuit that converts the strain of a strain body into an electrical signal, and four strain gauges 2, 2, and 3 are connected to the strain body. 2' and 3.3' are connected to each other, one of the voltage supply terminals is grounded, and the other voltage supply terminal is supplied with the voltage Vex.

10 is a first operational amplifier that receives the distortion signal from the bridge circuit 1 via the switch S1, the non-inverting input terminal is connected to the output terminal of the bridge circuit 1 via the switch Sit, and the inverting input terminal is connected to the resistor]]. It is connected to the output terminal via the resistor 12 and grounded via the resistor 12.

14 is a second operational amplifier that receives the distortion signal from the bridge circuit 1, the non-inverting input terminal is connected to the other output terminal of the bridge circuit 1 via the switch S2, and the inverting input terminal is
It is connected to an output terminal via a resistor 15 and to an output terminal of a reference voltage generation circuit 26, which will be described later, via a resistor 16. The non-inverting input terminals of these operational amplifiers 10 and 14 are connected through a series circuit of switches S3 and S4, and voltage is applied to resistors 19, 20, and 21 forming a voltage dividing circuit through a switch 55. A temperature-sensitive resistance element 18 is connected between the inverting input terminals and the inverting input terminals.

23 and 24 are resistors forming a voltage dividing circuit, and switch S6
, and input to the operational amplifier 25 via the switch S78,
It constitutes the reference voltage generation circuit 26 mentioned above.

These switches S1, S2, S3, S4, S5, S6
, S7, switches S3, S4, and S6 are turned on in the self-diagnosis mode by a signal from the switch control circuit 43;
In addition, the switches S1, S2, S5, and S7 are in the 0FFC state shown in Figure 1), and the switches S1, S7 are in the state shown in Fig. 1 in the weight measurement mode.
2. S7 is ON, and switches S3, S4, S5, S6
is OFF (the state shown in Figure 2), switches S3, S4, and S7 are ON in the offset voltage measurement mode, and switches S1, S2, S5, and S6 are OFF (the state shown in Figure 3), and the switches are in the temperature detection mode. S4, S5, S7
is ON, and switches S1, S2, S3, and S6 are OFF
(the state shown in FIG. 4).

The output terminals of these operational amplifiers 10 and 14 are connected to the inverting input terminal of the operational amplifier 32 via resistors 3o and 31, respectively.
Connected to the non-inverting input terminal. This operational amplifier 32
The inverting input terminal is connected to the output terminal via a resistor 33, and the non-inverting input terminal is grounded via a resistor 34 to form a differential amplifier circuit, and the output signal is output to a subsequent signal processing circuit (not shown). I'm here.

In this embodiment, when the power source of the meter body (not shown) is turned on and the start conditions are satisfied, a check signal is output from the switch control circuit 43, and the switches S3, S4,
S6 is ON, and switches S1, S2, S5, and S7 are O
FF (FIG. 1), thereby cutting off the connection between the bridge circuit 1 and the first and second operational amplifier circuits 10.14. The non-inverting input terminal of the operational amplifier 10 is short-circuited, and the operational amplifier 10
．． The output of 14 no longer depends on the output voltage of bridge circuit 1. In this state, the reference signal from the reference voltage generation circuit 20 is transmitted to the second operational amplifier 1 via the switch S6 and the resistor 16.
A signal equivalent to the reference weight is input to the inverting input terminal of the first operational amplifier 10 via the temperature-sensitive resistance element 18 to the inverting input terminal of the first operational amplifier 10 . Operational amplifier 1
0, ]4 is input to the differential amplifier circuit 32 via resistors 30 and 31. The output signal from the differential amplifier circuit 32 is sent to a level conversion circuit, which constitutes a subsequent signal processing circuit.
The signal is input to a filter circuit, an analog-to-digital conversion circuit, etc., treated in the same manner as a weight signal, and displayed as weight on a display.

By the way, l! on either of these signal paths! If jI an has already occurred, the output of the reference signal generating circuit 20 cannot be displayed as the reference weight, but the operator can recognize that a fault has already occurred in the signal processing system.

In this way, when the circuit function check is completed, the switch control circuit 43 turns on the switches S], S2, and SA, and turns off the switches S3, S4, S5, and S6.
F (as shown in FIG. 2), the reference signal generation circuit 20
While keeping the signal at the ground level, the output terminal of the bridge circuit 1 is connected to the first,
It is connected to the second operational amplifier 1o, 14.

When an item 8 is placed on a weighing device (not shown) in this state, the weight signal from the bridge circuit is detected by the differential amplifier circuit 32 via the operational amplifiers 1o and 14, and subjected to predetermined signal processing. It will be displayed as weight.

Roughly speaking, when the amplifier offset voltage detection mode is selected to detect the offset voltage of the amplifier circuit 10, ]4,
Switches S3, S4, S7 are ON, master switch S1,
Since S2, S5, and Si are set to OFF (the state shown in FIG. 3), an output corresponding to the offset voltage of the operational amplifier 10, ]4 is obtained, so the circuit constants etc. are set in accordance with this signal. Can be adjusted.

Roughly speaking, in the temperature detection mode for detecting the temperature of the strain body equipped with the bridge circuit 1, the switches S4, S5, S
7 is ON, and switches S1, S2, S3, and S6 are OFF.
By setting F (the state shown in FIG. 4), the operational amplifiers 1o and 14 are separated from the bridge circuit 1 by switches S] and S2, and the switch S is connected between the non-inverting terminals.
3, separated by S4, roughly the second operational amplifier 1
The inverting input terminal of No. 4 is also maintained at ground level. As a result, the operational amplifier 10.14 receives a voltage dependent on the resistance value of the temperature-sensitive resistance element 8, that is, a temperature-dependent voltage, at its inverting input terminal. Therefore, by converting this into temperature and displaying it, it becomes possible to measure and display the current temperature.

Next, the output voltage at each point of the circuit is calculated from Figures 1 to 4, respectively.
The operational amplifier 3 in each mode is taken as shown in the figure.
The above operation will be explained in detail by solving for the output signal v9 from 2.

Self-diagnosis mode VB=■+s”vos+ Vtg=V+s+VO52 Vs*=V7s+Vosx (However, VO5 is V., 2 is the operational amplifier 10 respectively.
．． 14, VoB3 represents the offset voltage of the operational amplifier 32 and vo, 4 represents the offset voltage of the operational amplifier 25) Fl.

−□・V□] +vO13 core an By the way, the value Rf2 of the feedback resistor 11 of the operational amplifier 10,
Feedback resistance of operational amplifier 14 ] 5 value R4, value of grounding resistance 12 of operational amplifier 10 Rb12, value of coupling resistance 16 between operational amplifier 14 and reference voltage generator circuit 26 Rbll, difference If] inversion of amplifier 32 Value R of input resistance 30 of input terminal
6°, the value R64 of the feedback resistor 33, the value R0 of the input resistor 31 of the non-inverting input terminal, the value F1m3 of the grounding resistor 34 as Rr+
=Rf2=Rf, day. 4/R, □= Ra3/ Rd+
,Day. , :Rb12. = day. 1 (If this setting is made, then the relationship will be 1. If the offset voltage is ignored, Vss will represent the reference signal.

Weight measurement mode Tsui V211=　　　　□　V*x”Vos2R1・Ro V Iy = V 1w+. ,1 V@y=v711+. .

V engineering=. 54 By the way, day 1. = day r2”Rft day d4/Rd2=
Ra3/ Ra 7, Sun. I=RI112=day5. The relationship becomes (when the resistance value is set,

Here, if R,=R1Δday·,day,=R−Δday, then, if the offset voltage V9m is ignored, 79w represents a voltage proportional to the load.

Offset voltage detection mode V3a=V+m+Vos+ 2a　;V　Is　　”　VOI2 Vaa=V, a+Vots V@11=V6@4 A relationship is established.

Here, Rfl'' day f2=day, , R, 4/day d2=R,
3/R,,,Rb++ =Rh+2=day. , and solve for V9a by setting the resistance value in the relationship that becomes, then V9
a represents the sum of the offset voltages of the amplifier 〇, ]4.25.32.

5 contribution detection mode V3. =l I ” vat I V@t=Vt++ Voti at=Vota R,l −□・.t) +V6t33 Rh++ By the way, Rfl: day q2= Rf, Ra4/ Rd
□”Ras/Rd+,Rゎll=Rh+2=day.1
When the resistance value is set, the following relationship is obtained.If the offset voltage 8. is ignored, v3w becomes a voltage that depends on the temperature-sensitive resistance value, and represents the temperature.

As described above, the feedback resistors 11 and 1 of the operational amplifier 10.14
5 are equal, the grounding resistor 12 and the resistor 1 supplying the reference voltage
6 are equal, roughly the ratio of the resistor 31.34 connected to the non-inverting input terminal of the operational amplifier 32, the feedback resistor 33 and the resistor 3.
By making the ratio equal to 0, impedance matching can be achieved and drift detection, self-diagnosis, temperature detection, and metering operations can be performed without mutual interference.

In this embodiment, the reference voltage is input to the operational amplifier 14 that maintains the connection state with the bridge circuit 1, but the reference voltage is input to the inverting input terminal of the other operational amplifier 10 via the inverting amplifier. It is clear that the same effect can be achieved.

Fig. 5.6.7 shows a second embodiment of the present invention, and the reference numeral 40 in the figure is a bridge circuit that converts the strain of the flexure element into an electric signal. Two strain gauges 2.2
', 3.3°, respectively, one of the voltage supply terminals is grounded via a temperature-sensitive resistor 4, and the other voltage supply terminal is configured to supply voltage Vx via a temperature-sensitive resistor 5. has been done.

41 is a switch 81 for transmitting the distortion signal from the bridge circuit 40.
1, the non-inverting input terminal of which is received via the switch S11! The inverting input terminal is connected to the output terminal of the bridge circuit 40 via a resistor 42, to the power supply Vex via a resistor 43, and to ground via a resistor 44.

45 is a second operational amplifier that directly receives the distortion signal from the bridge circuit 40 at its non-inverting input terminal; A resistor 4 is connected to the output terminal of a reference voltage generating circuit 55, which will be described later, through
8 to the power supply Vex, and the non-inverting input terminal is connected to the output terminal of the bridge circuit 1. The non-inverting terminals of these operational amplifiers 10 and 14 are connected via a switch S12, and a resistor element 50 is connected between the inverting input terminals.

55 is the reference voltage generation circuit mentioned above, which generates the voltage Vex! from the stabilized power supply. The resistors 51 and 52 divide the voltage to a predetermined value, for example, a voltage vO corresponding to the reference weight, and the switch 51
38 to the buffer amplifier 57, and is grounded by a switch S14 which operates inversely to the switch S13.

These switches S]], S12, 513, and S14 are
A signal from the switch control circuit 58 turns off switches 811 and S14 and turns on switches S12 and S13 in the self-diagnosis mode (Fig. 5), and turns off switches S12 and S13 and switches Sll and S13 in the weighing mode.
14 is turned on (Fig. 6), switch Sll is turned off in the amplifier offset voltage detection mode, 513 is turned off, and switch S is turned on.
12, S14 is switched ON (FIG. 7).

The output terminals of these operational amplifiers 41.45 are connected to the inverting input terminal of the operational amplifier 63 via resistors 60.6, respectively.
Connected to the non-inverting input terminal. This operational amplifier 63
The inverting input terminal is connected to the output terminal via a resistor 64, and the non-inverting input terminal is grounded via a resistor 65 to form a differential amplifier circuit. Forms an input impedance type differential amplifier circuit,
The output signal is output to a subsequent signal processing circuit (not shown).

In this embodiment, when the power source of the meter body (not shown) is turned on and the start conditions are satisfied, a check signal is output from the switch control circuit 5, and the switches S11 and S
14 is turned off, and the switches S12 and S13 are turned on (as shown in FIG. 5), and the second operational amplifier 4 is turned off.
The reference signal from the reference voltage generation circuit 55 is output with the non-inverting input terminal of 1.45 short-circuited. This reference signal is inputted via a resistor 47 to the inverting input terminal of the second operational amplifier 45, via a precision resistor 50 to the inverting input terminal of the first operational amplifier 41, and to the reference weight input terminal of the operational amplifier 41.45. Input a corresponding amount of signal.

Outputs from the operational amplifiers 41 and 45 are input to a differential amplifier circuit 63 via resistors 6o and 61. The output signal from the differential amplifier circuit 63 is input to a subsequent level conversion circuit, a filter circuit, an analog-to-digital conversion circuit, etc., and is treated in the same way as a weight signal and displayed as a weight on a display.

By the way, if a failure occurs in any of these signal paths, the output of the reference signal generation circuit 55 cannot be displayed as the reference weight, so the operator can determine that a failure has occurred in the middle of the signal processing system. be able to recognize that.

When the circuit function check is completed in this way, the switch control circuit 58 turns on the switches S11 and S14 and turns off the switches 512 and S13 to keep the signal from the reference signal generation circuit 55 at the ground level. At the same time, the output terminal of the bridge circuit 40 is connected to the first and second operational amplifiers 41 and 45 (the state shown in FIG. 6).

When a weighing device (not shown) is placed in this state, the weight signal from the bridge circuit 40 is transmitted to the operational amplifiers 4 and 4.
5, the difference is detected by the differential amplifier circuit 63,
After undergoing predetermined signal processing, it will be displayed as weight and 1 no.

Roughly speaking, if the iWm offset voltage detection mode is selected to detect the offset voltage of the amplifier circuit 41, 45, 63, etc. (Fig. 7), an output corresponding to the offset voltage of the operational amplifier 41, 45 can be obtained. Therefore, circuit constants etc. can be adjusted in response to this signal.

Next, calculate the output voltage at each point of the circuit as shown in Figures 5 to 7, respectively.
The operational amplifier 3 in each mode is taken as shown in the figure.
The above operation will be explained in detail by solving for the output signal v9 from 2.

Self-diagnosis mode V31 = 1s + Voz + V2s = V + s + Vosz VH = 1 g + V O * 3 (However, Vos + 5 Vos2 are each operational amplifier 4
], 45, vo, 3 is the operational amplifier 63 and VO54
represents the offset voltage of the operational amplifier 57).

By the way, the value Rf2 of the feedback resistor 42 of the operational amplifier 41,
The value Rf+ of the feedback resistor 46 of the operational amplifier 45, the value R11□ of the grounding resistor 44 of the operational amplifier 41, the value Bb l I of the coupling resistor 47 between the operational amplifier 45 and the reference voltage generation circuit 55.
, the value Rd2 of the input resistance 60 of the inverting input terminal of the differential amplifier 63, @R24 of the feedback resistor 33, the value Rdl of the input resistance 61 of the non-inverting input terminal, and @R63 of the grounding resistor 65.
1=Day t2=Rfz Rda/ Ra2= Rd3/
Ra7. When Ry=Rbtz=dayl is set in a muddy relationship, it becomes as follows.If the offset voltage is ignored, VB2 represents the reference signal.

Total mode Viw=V+w”Vou Engineering; V? ll+Va.

V6w=Vosa A relationship is established.

Here, each resistor is set to the same relationship as described above, and R,=day ΔR1 day=R−ΔR, and v9. Solving for , it becomes , and if the offset voltage v9□ is ignored, the voltage becomes proportional to the load. - Amplifier offset voltage detection mode V3a = V + a + Vos + V2a = V1a + Voi2 V6a = Via 10V. ! 3 vaa=vo14 The following relationship holds true.

Here, Rf, = day f2 = Rf, day d4/day d2 = day d
3/ Rd I, Rb, + = R1112 = day. The following relationship (when this resistance value is set and solved for V9m, g1 is the operational amplifier 4), represents the sum of the offset voltages of 45.63.57.

As described above, the feedback resistors 42 and 4 of the operational amplifiers 41 and 45
6 are equal, the grounding resistor 44 and the resistor 4 supplying the reference voltage
Impedance matching can be achieved by making the ratio of the resistors 61 and 65 connected to the non-inverting input terminal of the operational amplifier 63 equal to the ratio of the feedback resistor 64 and the input resistor 60. , drift detection, self-diagnosis, and metering operations can be performed without mutual interference.

In this embodiment, the reference voltage is input to the operational amplifier 45 that maintains the connection state with the bridge circuit 4, but the reference voltage is input to the inverting input terminal of the other operational amplifier 4 through the inverting amplifier. It is clear that the same effect can be achieved even if input is performed.

(Effects of the Invention) As described above, in the present invention, the output terminals of the bridge circuit including the strain gauge are connected to the input terminals of the high input resistance differential amplifier circuit through the switch means, and The output terminal of a voltage generation circuit that outputs a reference voltage is connected to the inverting input terminal of the input resistance differential amplifier circuit via a resistor, and the inverting input terminal of the other high input resistance differential amplifier circuit is connected to the resistor. Since it is grounded through a resistor with the same resistance, the signal input from the bridge circuit can be cut off by operating the switch even in a loaded state, and the reference voltage and ground potential can be selectively input to the high input operational amplifier. Therefore, it is possible to perform drift detection and self-diagnosis of the entire circuit system including the high-input differential amplifier circuit, and the reliability of the diagnosis results can be improved.

[Brief explanation of drawings]

1.2.3.4 are circuit diagrams illustrating an embodiment of the present invention in self-diagnosis mode, metering mode, offset voltage detection mode, and temperature detection mode, respectively, and 5.6.
7 shows other embodiments of the present invention in self-diagnosis mode,
FIG. 3 is a circuit diagram shown in a measurement mode and an offset voltage detection mode. 1-... Bridge circuit 2.2', 3.3'... Strain gauge 10.14... Operational amplifier 18... Temperature sensitive resistor 26... Reference voltage generation circuit S1 to S7... Switch applicant: Ishida Kouki Seisakusho Co., Ltd. Agent: Patent attorney: Katsuhiko Kimura, Keiji Nishikawa Figure 5 Figure 6 Figure 70

Claims (1)

[Claims] The output terminals of the bridge circuits including the strain gauges are respectively connected to the input terminals of the high input resistance differential amplifier circuit via switch means, and a reference voltage is output to the inverting input terminal of the one high input resistance differential amplifier circuit. A self-diagnosis circuit comprising an output terminal of a voltage generating circuit connected through a resistor, and an inverting input terminal of the other high input resistance differential amplifier circuit being grounded by a resistor having the same resistance as the resistor.