JP2709122B2 - Pressure sensor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure sensor, particularly to a pressure sensor having a circuit for amplifying a voltage output of a pressure-sensitive element.

(Prior Art) A pressure sensor is sometimes provided to know the hydraulic pressure of a hydraulic cylinder.

To explain this in Figure 4, the pressure-sensitive element 2 of the sensing unit 1 is a device for converting a change in pressure in the electrical resistance, when the resistance value R _S, the other three reference resistance 3
To 5 form a bridge connected in series. One end of each lead wire is connected to connection points A to D of these four resistors, and the other ends are connection terminals a to d.

Here, when the power supply voltage (V _CC ) is supplied from the connection terminal a via the voltage regulator 6 and the connection terminal d is connected to the ground, if the bridge is balanced, B,
Although the point D becomes the same potential and no output is generated, if the value of R _S changes in accordance with the rise of the oil pressure, the bridge will be out of balance and a potential difference will appear between B and D. For this reason, if the potentials at the points B and D are output via a differential amplifier formed inside the HIC (hybrid integrated circuit) 7, this output becomes a signal corresponding to the oil pressure, that is, a sensor signal output. .

On the other hand, when the sensor signal output (V _SIG ) and the reference voltage (set by the variable resistor 8) are input to the comparator 9 and the transistor 10 is switched by the output from the comparator 9, V _SIG exceeds the reference voltage. At this point, the transistor 10 is turned on and an output (level output V _LEV ) is generated on the collector side of the transistor 10, so that the pressure level can be determined for _{VSIG based} on the reference voltage.

(Problems to be Solved by the Invention) In such a pressure sensor, if the operating points of the comparator 9 vary, the determination of the pressure level is not stable even if the sensor signal output is the same. Therefore, the variable resistor 8 is configured to generate a reference voltage, and a sensor signal output output when a predetermined pressure is applied to the pressure-sensitive element 2 is used as a reference value to set the value of the variable resistor 8 (that is, the reference value). By adjusting the voltage, the same pressure level is determined for the same sensor signal output.

Here, in order to absorb the variation of the comparator 9, the reference voltage must be adjusted. For this purpose, a predetermined pressure must be actually applied to the pressure-sensitive element 2, so that a pressure tester is required. In addition, there is an annoyance that the sensing unit must be attached to the pressure verifier.

If the comparator 9 has a large hysteresis, the pressure level cannot be determined accurately. For example, if the input / output characteristics of the comparator are shown in FIG. 5, the output is different between the case where the input is large and the case where the input is small, and the difference (L in the drawing) is the width of the hysteresis. In this case, if the width of the hysteresis is large, it is difficult to match the center (that is, the reference voltage) with the reference value (the sensor signal output that is output when a predetermined pressure is applied to the pressure-sensitive element 2). It becomes.

The present invention has been made in view of such a conventional problem, and has a periodic waveform (for example, a rectangular waveform) offset by a voltage equivalent to a sensor signal output generated when a predetermined pressure is applied to a pressure-sensitive element. It is an object of the present invention to provide a sensor that adjusts a reference voltage by inputting a voltage of a wave or a triangular wave) to a comparator instead of a sensor signal output.

(Means for Solving the Problems) The present invention provides a voltage source (constant voltage source) for applying a constant voltage to a bridge in which a pressure-sensitive element and three reference resistors are connected in series, and a connection point where a constant voltage acts. An amplifier for inputting each potential between both adjacent connection points and outputting an output according to the potential difference, and means for variably setting a reference voltage to be input to the comparator (for example, comprising a constant voltage source and a variable resistor) ,
In a pressure sensor including a comparator that determines a pressure level by comparing the reference voltage with an output voltage from the amplifier, the pressure sensor is offset by a voltage corresponding to the pressure level and is wider than a hysteresis width of the comparator. Means for setting a periodic waveform voltage having a large amplitude as a reference value (for example, a variable resistor that divides a constant voltage source to generate an offset voltage, a transmitting circuit that outputs a periodic waveform voltage signal, , A circuit (for example, a switch) for switching between the set voltage and the amplifier output and inputting it to the comparator, and a means (for example, LED or Lamp).

(Operation) In adjusting the reference voltage to be input to the comparator, the setting voltage from the voltage setting means is input to the comparator instead of the amplifier output by the switching means.

When the reference voltage is adjusted so that the lamp blinks while watching a lamp that is turned on by a high-level signal from the comparator, for example, a means for informing the judgment result of the comparator, the center of the hysteresis of the comparator is offset voltage. Approaching.

Here, in order to adjust the reference voltage, it is not necessary to actually apply pressure to the pressure-sensitive element.

Moreover, the means for informing the judgment result of the comparator is LE
In the case of D or a lamp, if the reference voltage is adjusted so that they blink, the operation is completed, so that the adjustment operation is easy and can be performed with high accuracy.

(Embodiment) FIG. 1 is an embodiment corresponding to FIG. 2, and the same parts as those in FIG. 2 are denoted by the same reference numerals.

In the figure, before a branch point E for inputting a sensor signal output (V _SIG ) to a comparator 9, contacts e and f are provided.
And a level adjusting circuit 15 is connected to the contact f. Here, when the contact e is closed,
When the sensor signal output is input to the comparator 9 and the contact f is closed, the voltage set by the level adjustment circuit 15 is input to the comparator 9.

The level adjusting circuit 15 includes a transmitting circuit 16 that generates a sawtooth waveform voltage, a variable resistor 17 that generates a voltage for offsetting the voltage waveform by a predetermined value, and a combination of the offset voltage and the sawtooth waveform voltage. And an amplifier 18 to be inputted.

As the voltage set by the resistor 17, a voltage equivalent to a sensor signal output generated by a predetermined pressure applied to the pressure-sensitive element 2 is employed. For this purpose, the relationship between the pressure applied to the pressure-sensitive element 2 and the sensor signal output is measured in advance, and the voltage to be set is determined with reference to this relationship. Further, the amplitude of the sawtooth wave generated by the oscillation circuit 16 is set to be larger than the hysteresis width (L described above) of the comparator 9.

The switch 11 may be integrally formed as a part of the hybrid integrated circuit, or may be provided outside. The same applies to the level adjustment circuit 15.

Reference numeral 21 denotes a light-emitting diode (LED) that is turned on by a high-level signal from the comparator 9 and turned off by a low-level signal, for example, according to the determination result of the comparator 9.

With this configuration, when adjusting the reference voltage input to the comparator 9, the switch 11 is switched to close the contact f, and the output from the level adjustment circuit 15 is input to the comparator 9. Then, the resistance value of the variable resistor 8 is changed so that the LED 21 blinks.

When LED21 described further Figure 2 how to blink the, whereas sawtooth wave located above by a voltage (V _OFFSET) component that is offset, the characteristics of the comparator 9 (i.e. hysteresis position), the reference voltage By changing, it moves up and down in the figure. Note that L is the width of the hysteresis, and W is the amplitude of the sawtooth wave.

By the way, for the comparator 9 having a large L, the center of the hysteresis (indicated by a two-dot chain line) is desired to coincide with V _OFFSET (indicated by a one-dot chain line). Therefore, what should be done is to raise or lower the reference voltage so that the position of the steresis falls within the amplitude of the sawtooth wave as shown in the figure.
LED21 blinks. That is, if the LED 21 is made to blink, the center of the hysteresis can be brought closer to V _OFFSET . Here, for adjusting the reference voltage, it is not necessary to actually apply pressure to the pressure-sensitive element 2, so that a pressure verifier becomes unnecessary, and the trouble of attaching the sensing unit 1 to this verifier is released. .

In addition, since the adjustment of the reference voltage is performed with reference to the visualization signal that the LED 21 blinks, the adjustment operation is easy and can be performed with high accuracy.

On the other hand, according to FIG. 2, although the center of the hysteresis is close to V _OFFSET , it does not completely match. Therefore, as shown in FIG.
By adjusting the reference voltage up and down so that the waveform of the sawtooth wave is symmetrical and the ratio of the _ON time (T _ON ) and the OFF time (T _OFF ) of the LED 21 is equal, the center of the hysteresis is completely set to V _OFFSET. Can be matched.

Further, since the variable resistor 17 is used in determining the offset voltage V _OFFSET , the pressure level determined by the comparator 9 can be adjusted arbitrarily.

Finally, although the embodiment has been described using a sawtooth wave, a square wave may be used. Further, in addition to the LED, a lamp or a buzzer may be used.

(Effect of the Invention) In the present invention, a voltage of a periodic waveform offset by a voltage corresponding to the pressure level determined by the comparator and having an amplitude larger than a hysteresis width of the comparator is set as a reference value. Means, means for inputting the set voltage to the comparator instead of the sensor signal output, and means for informing the determination result of the comparator are provided, so that even if the pressure-sensitive element is not actually applied with pressure, Since the reference voltage to be input to the comparator can be adjusted, the adjustment operation is facilitated, and the reference voltage can be adjusted with high accuracy even when the hysteresis of the comparator is large.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, FIGS. 2 and 3 are waveform diagrams for explaining the operation of this embodiment, FIG. 4 is a circuit diagram of a conventional example, and FIG. FIG. 4 is a waveform diagram illustrating input / output characteristics. DESCRIPTION OF SYMBOLS 1 ... Sensing part, 2 ... Pressure sensitive element, 3-5 ... Reference resistance, 6 ... Regulator, 7 ... HIC, 8 ... Variable resistance, 9 ... Comparator, 10 ... Transistor, 11 ...
Changeover switch, 15: Level adjustment circuit, 16: Transmission circuit, 17: Variable resistor, 18: Amplifier, 21: LED.

Claims (1)

(57) [Claims] 1. A voltage source for applying a constant voltage to a bridge in which a pressure-sensitive element and three reference resistors are connected in series, and potentials between two adjacent connection points to which a constant voltage is applied are inputted. An amplifier that outputs according to the potential difference, and a unit that can variably set a reference voltage input to the comparator;
In a pressure sensor including a comparator that determines a pressure level by comparing the reference voltage with an output voltage from the amplifier, the pressure sensor is offset by a voltage corresponding to the pressure level and is wider than a hysteresis width of the comparator. Means for setting a voltage of a periodic waveform having a large amplitude as a reference value, means for switching between the set voltage and the amplifier output and inputting the voltage to the comparator, and means for notifying the judgment result of the comparator are provided. Pressure sensor.