JPS6353599B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal transmitter that converts various process quantities into electrical signals and transmits the electrical signals to a remote receiving section or the like.

Conventional examples of such signal transmitters include U.S. Patent No. 3646583 and No. 518536.
In U.S. Patent No. 3646583, a carrier wave is vibrationally modulated by a change in the electrical state of a detector that detects a process amount, and this is detected and then smoothed.
A DC signal corresponding to the process amount is obtained, and in U.S. Patent No. 518536, the time required to charge the capacitance of a capacitive detector is measured and an electrical signal is generated based on this time width. are doing.

However, in the former case, it is necessary to compensate for the temperature characteristics of the detection diode, and it is necessary to select and use diodes with uniform temperature characteristics.In addition, it is necessary to feed back the electrical signal from the output side to the input side, and to use a high-precision resistor. Since the balance between input and output is obtained by a circuit network using values, productivity is low and production costs cannot be reduced easily.

Furthermore, the latter method requires a high-speed and highly accurate level comparator, which has the drawback of making it difficult to reduce production costs.

The present invention has the purpose of fundamentally eliminating such drawbacks of the conventional ones, and provides an extremely effective signal transmitter that can easily reduce production costs by having a configuration based on digital circuits. It is something to do.

Hereinafter, details of the present invention will be explained with reference to figures showing examples.

In the circuit diagram of FIG. 1, a differential capacitance type detector 4 is configured by fixed electrodes 1 and 2 and a movable electrode 3, and the movable electrode 3 is
moves between fixed electrodes 1 and 2, the capacitance C 1 between fixed electrode 1 and movable electrode ₃ and the capacitance C 2 between fixed electrode 2 and movable electrode ₃ are differential. It has become a subject of constant change.

In addition, integrated circuit NAND gates are used as the inverters 11 to 14, and similar switches 15 to 18 are used, and during the count output of the counter 19, the most significant bit Q ₁ and the adjacent lower bit Q ₆ and the most significant bit Q ₇
Negative feedback is given to the pulse signal obtained from the output current according to the output current.

That is, the inverters 11 and 12 and the resistor 20 constitute a relaxation type oscillator, and the most significant bit _Q7 of the counter 19 causes the inverter 13 to
Switch 1 controlled with or without
capacitance connected to the oscillator by 5,16
While switching C ₁ and C ₂ , the integrating circuit consisting of resistor 21 and capacitor 22 has lower bit Q ₆ .
The switch 17,1 as a composite circuit is controlled with or without the inverter 14 by
8 provides a signal obtained by inverting the pulse signal from the most significant bit _Q7 by an inverter 13, and a feedback signal obtained from an output current feedback potentiometer 31.

The output of the integrator circuit is applied to the non-inverting input of the operational amplifier 32 constituting the output section, and is amplified as a difference between the reference voltage Es obtained by dividing the power supply voltage +E by the potentiometer 33, and is then applied to the FET ( Fie
-ld Effect Transistor.) 34, thereby varying the current from the receiving section etc. that flows between the output terminals 35 and 36 via a two-wire line,
This is used as an output current as a predetermined electric signal.

Further, a constant voltage is obtained by a constant voltage diode 37 inserted in series with the FET 34, and this is set as the power supply voltage +E.

Therefore, in the oscillator, the counter 19
When the most significant bit _Q7 of is "L" (low level), the switch 15 is turned on, and a frequency _f1 as the first frequency corresponding to the capacitance _C1 is generated, and by counting this, the most significant bit _Q7 is “H” (high level)
When the switch 16 is turned on, the second frequency f ₂ corresponding to the capacitance C ₂ is generated, and in order to repeat this, the counter 19 changes the frequency.
Counting of f ₁ and f ₂ is performed alternately, but the pulse signal from the most significant bit Q ₇ is inverted by the inverter 13 and is turned “H” and “L” at twice the frequency of the most significant bit Q ₇ . Iterate lower bits
The switch 17 is controlled by the pulse signal from Q ₆ , and the switch 18 is turned on when the switch 17 is turned off. During this period, the feedback voltage E _f from the potentiometer 31 is It is inserted as a feedback signal, and the feedback signal is synthesized by this.

In addition, inverters 11 to 14 and counter 1
9 has CMOS (Complementary Metal Oxide)
Semiconductor.) type circuit is used, and the output peak value of the switch 17 is approximately equal to the power supply voltage +E. Therefore, as shown in A pulse signal having a peak value of the power supply voltage +E is obtained.

Also, since the lower bit Q ₆ adjacent to the most significant bit Q ₇ controls on/off of the switches 17 and 18, the period corresponding to the frequency f ₁ is
The period T ₂ corresponding to the frequency T ₁ and the frequency f ₂ is 1/2 of the period in which the feedback voltage E _f is inserted in the negative direction, and in response to the movement of the movable electrode 3, the As shown, the periods T ₁ and T ₂ change differentially.

However, due to the negative feedback effect caused by the insertion of the feedback voltage E _f , the area of the negative waveform due to the feedback voltage E _f is equal to the area of the positive waveform due to the power supply voltage +E, as shown in Figure 2 c, resulting in equilibrium. And the voltage obtained by averaging this signal and the voltage of potentiometer 3
Since the difference from the reference voltage Es set by 3 is proportional to the feedback voltage E _f , the following equation holds true.

E _s −+E・T ₁ /2 (T ₁ +T ₂ )=E _f ...(1) Therefore, in the equilibrium state shown in equation (1), T ₁ /
An output current corresponding to (T ₁ +T ₂ ) can be obtained, and the purpose can be achieved.

Furthermore, if the feedback voltage E _f is synthesized to the output side of the inverter 13 via a resistor etc. without intermittent switching by the switches 17 and 18, the pulse signal shown in FIG. 3 is obtained, and the same balancing effect as described above is obtained. Therefore, as the movable electrode 3 moves, the waveform changes as shown in FIGS. 3a and 3b, and is balanced in the state shown in FIG. 3b, which is expressed by the following equation.

E _R −+E・T ₁ /T ₁ +T ₂ =−E _f・T ₂ /T ₁ +T ₂ ……(2
) In this case, the conversion characteristic between input IN and output OUT becomes non-linear, as shown in FIG.

In addition, if positive and negative power supply voltages +E and -E are applied to the counter 19 in FIG. 1, and a backward pulse signal is generated in the count output, the output side waveforms of the switches 17 and 18 are as shown in FIG. The following equation holds true.

+E・1/2T ₁ /T ₁ +T ₂ +−E・1/2T ₂ /
T ₁ +T ₂ + (-E _f ) 1/2 = E _s +E・T ₁ -T ₂ /T ₁ +T ₂ -E _f
=2E _s E _f =+E・T ₁ −T ₂ /T ₁ +T ₂ −2E _s ……(3) In other words, in any of equations (1) to (3), the period
Since fluctuations in the same direction and evenly in T ₁ and T ₂ are eliminated, periods T ₁ and T ₂ correspond to frequencies f ₁ and f ₂ , and frequencies f ₁ and f ₂ correspond to capacitances C ₁ and C _2. By correspondingly, changes in capacitance C ₁ and C ₂ due to temperature fluctuations other than the process amount to be detected do not appear in the output current, and accurate process amount measurement results can be obtained.

In addition, the relationship between the most significant bit _Q7 and the lower bit _Q6 in the count output of the counter 19 does not necessarily have to be the most significant bit _Q7 and the adjacent lower bit _Q6 ; The upper bits may be fed to the integrating circuit; if the counter 19 is a binary counter, the output of the lower bits has a frequency 2n times that of the upper bits, so any lower bits can be used.

In addition to using a differential capacitance type detector 4 as a detector, a combination of a variable capacitance element and a fixed capacitance element may be used as long as both or one of the frequencies f ₁ and f ₂ can be varied according to the process amount. Alternatively, a variable resistance element such as a strain gauge or a resonator can be used.

Note that if a CMOS type is used for each circuit, a pulse signal with a peak value approximately equal to the power supply voltage +E/-E can be obtained, so it is possible to feed it directly to the integration circuit. The same thing can be done even if a circuit for converting into a pulse signal is provided.

However, since the CMOS type circuit consumes less power supply current, it is advantageous in a two-wire transmitter where line current is limited, and the circuit configuration can be simplified. In addition, various configurations of the output section can be selected.

As is clear from the above explanation, since the present invention is mainly composed of digital circuits, there are no problems such as component selection, no special adjustment is required, and manufacturing is extremely easy. Great effects can be obtained in the transmitter.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a waveform diagram of the waveform shown in Fig. 1, and Fig. 3 is a waveform diagram when feedback is performed without interruption in Fig. 1. , FIG. 4 is a diagram showing the conversion characteristics in the case of the waveform of FIG. 3, and FIG. 5 is a waveform diagram when a reverse pulse signal is generated from the counter in FIG. 1. 13, 14... Inverter, 17, 18... Switch (synthesizing circuit), 19... Counter, 21...
...Resistor, 22...Capacitor, 31...Potentiometer, 32...Operation amplifier, 34...
FET, 35, 36...output terminal.

Claims (1)

[Claims] 1 A counter that alternately counts first and second frequencies, at least one of which changes depending on the process amount, and a pulse signal from the upper bit in the count output of the counter according to a pulse signal from the lower bit with respect to the upper bit. a switch that inserts a feedback signal from the output side when the pulse signal from the upper bit is cut off, an integrating circuit that averages the output of the switch, and an integrating circuit that converts the output of the integrating circuit into a predetermined electrical signal. 1. A signal transmitter comprising: an output section for converting into .