JPH0126566B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an A/D converter connected to a detection circuit such as a strain gauge transducer. As a device of this type, the present applicant previously proposed a triple integral type conversion device consisting of the circuit shown in the first diagram. 1st
In the figure, a is a bridge circuit constituted by a resistor including a strain gauge, a pair of diagonal points of the circuit a are connected to a bridge power source c via a switch b, and a pair of diagonal points of the circuit a are connected to a bridge power source c via a switch b. was connected to the polarity inverter e via an amplifier d.

f is a changeover switch, g is a reference power supply, h is an integrator, i is a comparator that stops counter j from counting the clock pulses of clock oscillator k when the output of integrator h becomes zero, l is switch b, changeover switch f and controls the operation of counter j
It is the CPU.

First, switch b is opened, changeover switch f is connected to fixed contact a, and as shown in _FIG . _The unnecessary voltage _{E 0} such as Integrate the sum of the output Ei and the unnecessary voltage E ₀ to positive polarity. With the above operation, the unnecessary voltage E ₀ is erased, and only the output Ei is integrated. Next, switch b is opened, changeover switch f is connected to fixed contact c, and the reference power supply voltage E _R is integrated with the opposite polarity for a time T ₃ , and the integrator h
The integration is stopped when the output voltage of becomes zero, and the counter j, which started counting clock pulses from the start of interval _T3 by the CPU1 command, stops counting. Since the time _T3 is proportional to the output Ei, the output Ei becomes a digital value from the count result of the counter j.

By performing the triple integration as described above, the output of the bridge circuit a can be converted into a digital value without being affected by the unnecessary voltage _E0 , but the operating time is _T1 + _T2 + _T3 , which is, for example, 60 millimeters. There was an inconvenience that the speed could not be increased because it took about seconds. An object of the present invention is to provide an A-D converter free from such inconveniences, which comprises a polarity reversing circuit, an integrator, a reference power source, a circuit switching means, and a counting means, and is equipped with a polarity inverting circuit, an integrator, a reference power source, a circuit switching means, and a counting means. , the output voltage Ei of the detection circuit connected to the power supply is integrated for a predetermined time _T1 , and the output voltage of the detection circuit to which the power supply voltage is not applied during the time _T2 until the voltage becomes equal to the integrated voltage. integrating the sum of the inverted voltage -E ₀ by the polarity inverting circuit and the reference power supply voltage E _R of negative polarity; integrating the inverted voltage -E ₀ over time T ₁ -T ₂ ; The operation of the circuit switching means sequentially integrates the positive reference power supply voltage E _R during the time T ₄ until the voltage becomes equal to the voltage, and the counting means integrates the previous time T ₂ and the time T It is characterized by counting the difference from ₄ .

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

FIG. 3 shows a block diagram of one embodiment of the present invention. In FIG. 3, reference numeral 1 denotes a bridge circuit constituted by a resistor including a strain gauge. A pair of diagonal points of this circuit 1 are connected to a bridge power supply 3 via a switch 2, and the other pair of diagonal points are connected to a bridge power supply 3 via a switch 2. The corner points were connected to a polarity inversion circuit 5 via an amplifier 4. Reference numeral 6 denotes a changeover switch, the fixed contact a of which is connected to the amplifier 4 and the fixed contact b connected to the polarity inverting circuit 5. 7 is also a changeover switch, and its fixed contacts a and b are connected to the + and - terminals of a reference power source 8, respectively. 9 is an integrator; 10 is a comparator which uses its output to stop counting clock pulses from the clock oscillator 12 of the counter 11 when the integrated voltage of the integrator 9 becomes zero; 13,
The switch 2 and changeover switches 6 and 7 are controlled in the process described below, and the counter 11 starts counting up or down.
It is the CPU.

Next, its operation will be explained.

First, the switch 2 is closed by the CPU 13, the changeover switch 6 becomes the fixed contact a, and the changeover switch 7 becomes the fixed contact a.
are connected to the fixed contacts _c , and as shown in _FIG . It is integrated. After time T ₁ elapses, CPU
13, switch 2 is started, changeover switch 6 is set to fixed contact b, changeover switch 7 is set to fixed contact b
-E ₀
The sum of the negative polarity reference power supply voltage -E _R is integrated by the integrator 9 for a time T ₂ . At the same time as the start of this time _T2 , the clock oscillator 12 is activated by a command from the CPU 13.
The counter 11 that started counting up the clock pulses output by the comparator ₁ at the time T2 when the output of the integrator 9 became zero
Counting is stopped by outputting 0. Next, at this point, based on the output of the comparator 10, the CPU 1
3, only the changeover switch 7 is switched to and connected to the fixed contact c, so during the time _T3 when the total time with the time _T2 is equal to the time _T1 , the unnecessary voltage of negative polarity _-E0 is integrated. be done.

When this time T ₃ has elapsed, the unnecessary voltage E ₀ has been erased, but since the negative polarity voltage −E _R has been integrated as much as the integrated voltage during the time T ₃ , T ₂ is longer than the time corresponding to the output voltage Ei. Therefore, in order to subtract this amount, continue the following operation.

When time _T3 has elapsed, switch 2 remains open, and the CPU 13 connects changeover switch 6 to fixed contact c and changeover switch 7 to fixed contact a, until the output of integrator 9 becomes zero. Time of T ₄
During this time, the positive reference voltage E _R is integrated.
CPU 13 outputs comparator 1 at the beginning of time T ₄ .
Since a down-count command signal is applied to the counter 11 based on the polarity of the output of 0, the counter 11
performs down counting from the count value at time _T2 , and stops counting by the output of the comparator 11 when time _T4 has elapsed. The counting result of the counter 11 corresponds to time T ₂ - T ₄ , and since this period corresponds to the output voltage Ei, the counter 11 counts Ei
Outputs a digital quantity.

The above relationship can be expressed mathematically as follows.

At time T ₁ , E ₁ = 1/RC∫ ^T1 ₀ (E ₀ +Ei)dt=1/RC(E ₀ +Ei)T ₁ ……(1) At time T ₂ , −E ₁ = 1/RC∫ ^T2 ₀ (-E _R -E ₀ )dt=-1/RC(E _R +E ₀ )T ₂ ...(2) At time T ₃ , -E ₂ =1/RC∫ ^T3 ₀ (-E ₀ )dt= -1/RCE ₀・T ₃ ...(3) At time T ₄ , E ₂ = 1/RC∫ ^T4 ₀ E _R dt=1/RCE _R・T ₄ ...(4) Therefore, these equations From this, we get Ei=E _R T ₂ −T ₄ /T ₁ ……(5).

As is clear from this equation, since the reference power supply voltage E _R and the time T ₁ are known, the output voltage Ei is (T ₂ −
T ₄ ). Therefore, if the counter 11 counts the number of pulses corresponding to the time (T ₂ -T ₄ ), the output voltage Ei can be converted into a digital quantity.

As mentioned above, the unnecessary voltage E ₀ is the offset voltage of the amplifier 4 or the thermal electromotive force of the connection part, and is actually less than 1/100 of the full scale value of the output voltage of the bridge circuit 1. Therefore the integration time
If T ₁ is 20 ms, then T ₄ is less than 0.2 ms, and if T ₁ is 20 ms as in the previous proposal, the total conversion time T ₁ + T ₂ + T ₃ + T ₄ is
It takes 40.2 milliseconds, which is a short time.

In the above embodiment, the switch 2 was opened to remove the power supply voltage applied to the bridge circuit 1, but the power supply 3 was turned off so that the voltage of the bridge power supply 3 became zero.
It may also be controlled by the CPU 13.

Further, for controlling the switch 2, the changeover switches 6 and 7, and the counter 11, a control circuit combining a timer and other elements can be used instead of the CPU 13.

As described above, the present invention includes a polarity inverting circuit, an integrator, a reference power source, a circuit switching means, and a counting means, and in the integrator, the output voltage Ei of the detection circuit connected to the power source is maintained for a predetermined time _T1 . Integration and the inversion voltage by the polarity inverting circuit of the output voltage of the detection circuit during which no power supply voltage is applied during the time T ₂ until the voltage becomes equal to the integrated voltage -E ₀ and the negative reference power supply voltage E _R and integrating the sum of
Integrating the inverted voltage −E ₀ for a time T ₁ −T ₂ and the time required to reach a voltage equal to the integrated voltage.
The circuit switching means is operated to sequentially integrate the reference power supply voltage E _R of positive polarity during _T4 , and the counting means counts the difference between the time _T2 and the time _T4 . , similar to the previously proposed method, the output voltage of the detection circuit can be converted from A to D by removing unnecessary voltage due to the shift of the zero point of the amplifier, etc., and the conversion can be performed at a high speed comparable to that of the conventional double integration type. has.

[Brief explanation of drawings]

Figure 1 shows the triple integral type A- according to the applicant's proposal.
A block diagram of the D converter, Fig. 2 is a diagram showing each waveform of the input voltage and output voltage of the integrator, and Fig. 3 is a block diagram of the D converter.
This figure is a block diagram of one embodiment of the present invention, and FIG. 4 is a diagram showing each waveform of the input voltage and output voltage of the integrator. 1... bridge circuit, 2... switch, 3...
Bridge power supply, 5... Polarity inversion circuit, 6, 7...
Changeover switch, 8...Reference power supply, 9...Integrator,
10... Comparator, 11... Counter, 12
...Clock oscillator, 13...CPU.

Claims (1)

[Claims] 1 Equipped with a polarity inversion circuit, an integrator, a reference power supply, a circuit switching means, and a counting means, in which the output voltage Ei of the detection circuit connected to the power supply is controlled for a predetermined period of time.
During the integration period T ₁ and the time T ₂ until the voltage becomes equal to the integrated voltage, the inversion voltage −E ₀ by the polarity inversion circuit of the output voltage of the detection circuit to which no power supply voltage is applied and the negative polarity Integrating the sum of the reference power supply voltage E _R and the inversion voltage −E ₀ at time T _1
−T2 and integrating the positive reference power supply voltage E _R for a time _T4 until the voltage becomes equal to the integrated voltage are sequentially performed by operating the circuit switching means; An A/D conversion device characterized in that the counting means counts the difference between the time _T2 and the time _T4 .