JPH0944784A - Two-wire sensor and sensor structure using this - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a two-wire sensor circuit and a sensor structure which are capable of improving the versatility by extending applicable load by the increase of load current, while maintaining the condition by leaked current and internal dropped voltage to an optimum state and simplifying the assembling, improving the bend resistance and waterproof by a mold casting. SOLUTION: This circuit is made to be a two-wire sensor circuit to be used for the detection of the location of a fluid pressure actuating equipment and is composed of a bridge circuit 1 defining MR elements 1a to 1d as four sides, the amplifier 2 of this detection signal, a Darlington connection circuit 3 to be connected with the amplifier 2, a light emitting diode LED, PNP shape transistors Q1 and Q2 composed of mirror circuits, a resistance R1 and a constant current diode ID. In particular, the current IF flowing in the light emitting diode LED is determined by the VEB of the PNP shape transistors Q1 and Q2 and the value of the resistance R1 connected with these transistors in parallel and almost constant current is made to flow even if load changes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-wire type sensor circuit technology, and in particular, in a sensor circuit used as a position detection device for fluid pressure actuated equipment such as a cylinder, improvement in versatility and assembly due to increase in load current. The present invention relates to a two-wire sensor circuit suitable for simplification and improvement of environment resistance, and a technique effectively applied to a sensor structure using the same.

[0002]

2. Description of the Related Art For example, according to a study conducted by the inventor, a sensor circuit used for detecting the position of a fluid pressure actuated device includes a bridge circuit using an MR element, an amplifier for this output signal, and a detection / non-detection state. It is conceivable that the light emitting diode is configured to display, and the detection state can be confirmed by turning on the light emitting diode together with the signal output in the detection state or the non-detection state.

Further, a position detecting device using such a sensor circuit is used by being mounted on a fluid pressure operating device such as a cylinder, and the position detecting device is miniaturized with the miniaturization of the fluid pressure operating device to be detected. Also, while there is a trend toward miniaturization, further cost reduction, and specification reduction, in sensor circuits, leakage current, load current, and internal voltage drop are the main specifications.

For example, the actual Kaihei 7- proposed by the present inventor
In the two-wire sensor circuit described in Japanese Patent No. 2923, as shown in FIG. 7, a bridge circuit 1 having four sides of MR elements 1a to 1d and a sensor IC by an amplifier 2 for amplifying the detection signal are connected to a Darlington connection. The circuit 3, the light emitting diode LED, the PNP transistor Q1, the resistor R1, the constant current diode ID and the like are connected and configured.

[0005]

By the way, in the sensor circuit technology as described above, a dark current is prevented from flowing through the light emitting diode at the time of non-detection, and further, a voltage drop at the time of detection is corrected to ensure stable operation. However, among the main specifications of the sensor circuit, which are leakage current, load current, and internal voltage drop, it is conceivable that the model to be applied to relays will be limited due to the reduction of the load current.

A position detecting device using such a sensor circuit has a general-purpose S having a circuit structure as shown in FIG. 8, for example.
The MD component is mounted on the printed circuit board 7, and the printed circuit board 7 is housed in the case 8a, and is molded and assembled by injection of the resin material 11a from the side of the lead wire grommet portion 10a for external connection. In this case, it is conceivable that the fixed state of the lead wire grommet portion 10a is not stable and a problem occurs in the flexibility.

Therefore, an object of the present invention is to provide a load which determines the capacity of the load by a mirror circuit configuration of a pair of transistors while optimally maintaining the non-detection condition by the leakage current and the detection condition by the internal voltage drop as described above. It is an object of the present invention to provide a two-wire sensor circuit capable of increasing a current and expanding a load applied to a relay or the like to improve versatility.

Another object of the present invention is to simplify the assembly by mold casting from the opening in the opposite direction to the lead wire grommet portion of the printed circuit board, and to further improve resistance by mold casting of the lead wire grommet portion. An object of the present invention is to provide a sensor structure using a two-wire sensor circuit that can improve flexibility and water resistance.

The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

[0010]

SUMMARY OF THE INVENTION Among the inventions disclosed in the present application, the outline of a representative one will be briefly described.
It is as follows.

That is, the two-wire sensor circuit of the present invention is
It is used for position detection of fluid pressure operated equipment and is connected to an amplifier that amplifies a detection signal from a bridge circuit by a detection element, a Darlington connection circuit, a light emitting diode connected to this Darlington connection circuit, and this light emitting diode. A first transistor and a second transistor and a resistance element having a connected mirror circuit configuration;
A constant current diode connected to the first transistor, the emitter terminal and the resistance element of the first transistor and the second transistor having a mirror circuit configuration are connected to the signal terminal for external connection, and the common terminal is connected to the common terminal. It connects the emitter terminal of the Darlington connection circuit and the collector terminal of the second transistor.

With this circuit connection, when the Darlington connection circuit is turned on in the detection state by the detection element of the bridge circuit, the load current of the external load connected between the signal terminal and the common terminal is, for example, parallel connection from the signal terminal side. It flows to the common terminal through the first and second transistors of the mirror circuit configuration, the resistance element, the light emitting diode, and the Darlington connection circuit.

Here, the current IF flowing through the light emitting diode
Is [(voltage value between emitter and base of first and second transistors of mirror circuit configuration: VEB) / (resistance value of resistance element: R1) + 2 × (first and second transistors of mirror circuit configuration) Base current value: IB)],
The relationship between (VEB / R1) and 2IB is (VEB / R1) >> 2
Since it becomes IB, the current IF becomes almost constant. Therefore, even if the external load changes, a constant current flows in the light emitting diode and constant current driving is performed, so that a large load current as a sensor circuit can be obtained.

In this sensor circuit, the circuit configuration as described above determines the leakage current by the constant current diode when the detection element is not detected, and the bases of the first and second transistors when the detection element is detected. Since the output voltage of the detection signal can be determined by the voltage between the emitter terminals, the forward voltage of the light emitting diode, and the voltage between the collector and emitter terminals of the termination transistor of the Darlington connection circuit, non-detection conditions by leakage current, detection by internal voltage drop It is assumed that the conditions are kept optimal.

Further, the sensor structure of the present invention is constructed by incorporating the first transistor and the second transistor of the mirror circuit configuration in the same package, and mounting the two-wire type sensor circuit on the printed board. The opening of the case for accommodating the printed circuit board is provided in the opposite direction of the lead wire grommet portion for external connection connected to the printed circuit board.

With this sensor structure, when assembling the sensor, the printed circuit board can be housed in the case and then mold-molded from the opening, so that it can be manufactured from the opening opposite to the lead wire grommet. Mold casting simplifies the assembly, and since the lead wire grommet portion is also mold cast, the bending resistance and water resistance can be improved.

[0017]

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

FIG. 1 is a circuit diagram showing a two-wire type sensor circuit according to an embodiment of the present invention, and FIGS. 2A and 2B show a sensor using the two-wire type sensor circuit according to the present embodiment as a fluid. FIG. 3 is a sectional view showing an example of a sensor structure, FIG. 4 is an explanatory view showing load current characteristics, FIG. 5 is a characteristic view showing load current characteristics, and FIG. 6 is a cross-sectional view showing a modified example of the sensor structure.

First, the configuration of the two-wire type sensor circuit of the present embodiment will be described with reference to FIG.

The two-wire type sensor circuit of this embodiment is used, for example, for position detection of a fluid pressure operating device, and is provided with a signal terminal and a common terminal for outputting a detection signal from a bridge circuit by a detection element through an amplifier. A linear sensor circuit, a bridge circuit 1 having four sides of MR elements 1a to 1d (detection elements) sensitive to magnetic force, an amplifier 2 for amplifying a detection signal from the bridge circuit 1, and a Darlington connected to the amplifier 2. Connection circuit 3, light emitting diode LED, light emitting diode LE connected to Darlington connection circuit 3
It is composed of a pair of PNP type transistors Q1 and Q2 connected to D in a mirror circuit configuration, a resistor R1, and a constant current diode ID connected to the PNP type transistor Q1.

The emitter terminals of the PNP type transistors Q1 and Q2 and the resistor R1 having the mirror circuit configuration.
Is connected to the signal terminal OUT, the emitter terminal of the Darlington connection circuit 3 and the collector terminal of the PNP transistor Q2 are connected to the common terminal GND, and the current flowing through the light emitting diode LED is P in the mirror circuit configuration.
The constant current is determined by the emitter-base voltage of the NP transistors Q1 and Q2 and the resistance value of the resistor R1, and the leak current is determined by the constant current diode ID when the bridge circuit 1 does not detect the current, and at the time of detection. The output voltage of the detection signal is determined by the base-emitter terminal voltage of the PNP transistors Q1 and Q2, the forward voltage of the light emitting diode LED, and the collector-emitter terminal voltage of the termination transistor of the Darlington connection circuit 3. There is.

The Darlington connection circuit 3 is a circuit in which a plurality of transistors having the same polarity are directly connected to form a single transistor having an apparently excellent characteristic. The Darlington connection circuit 3 is in an ON state or a non-detection state when the bridge circuit 1 detects it. It is sometimes turned off and is composed of, for example, two NPN type transistors Q3 and Q4 and resistors R2 and R3. The base terminal of the first-stage NPN transistor Q3 is connected to the amplifier 2, the emitter terminal of the last-stage NPN transistor Q4 is connected to the common terminal GND, and both NPN transistors are connected.
The collector terminals of the transistors Q3 and Q4 are connected to the light emitting diode LED.

The light emitting diode LED is an indicator light which is turned on when the Darlington connection circuit 3 is ON during detection and is turned OFF when the Darlington connection circuit 3 is OFF during non-detection. The cathode terminal is connected to the Darlington connection circuit 3. The anode terminals are connected to PNP type transistors Q1 and Q2 having a mirror circuit configuration connected in parallel and a resistor R1.

The PNP transistors Q1 and Q2 having the mirror circuit configuration determine the current flowing through the light emitting diode LED by the resistor R1 connected in parallel, and at the time of detection, the light emitting diode LED and the Darlington connection circuit 3 are connected.
The output voltage is determined by the NPN-type transistor Q4, and two composite transistors contained in the same package are used. The base terminals of the PNP type transistors Q1 and Q2 are commonly connected to the light emitting diode LE.
The D and collector terminals are respectively connected to both ends of the bridge circuit 1, and the emitter terminals are commonly connected to the signal terminal OUT. Also, the collector of the PNP transistor Q1
A constant current diode ID is connected between the emitter terminals.

The constant current diode ID determines the leak current of the two-wire type sensor circuit when it is not detected, and its cathode terminal is connected to the emitter terminal of the PNP transistor Q1 and its anode terminal is connected to its collector terminal, respectively.

The bridge circuit 1, the amplifier 2 and the resistor R4 for adjusting the current or voltage in the present embodiment are used.
˜R6 are built in the sensor IC, and a capacitor C is inserted between the output terminals thereof, that is, between the signal terminal OUT and the common terminal GND, in consideration of the delay time, for compensation by external noise, and the surge voltage is further increased. A constant voltage diode D as a countermeasure is connected.

The components of these two-wire sensor circuits are mounted on a printed circuit board (not shown) using general-purpose SMD (surface mount device) components, and are further housed in a case to form a two-wire sensor. Position detecting device 4 and, for example, as shown in FIG.
(Fluid pressure actuated device) is fitted and mounted in the mounting groove 6 and used for detecting the position of the cylinder 5.

The structure of this two-wire sensor is shown in FIG.
As shown in FIG. 3, a general-purpose SMD component having a circuit configuration is mounted on the printed circuit board 7, and the opening 9 of the case 8 for accommodating the printed circuit board 7 has a lead wire grommet portion 10 for external connection connected to the printed circuit board 7. It is provided in the opposite direction. At the time of assembling the sensor, the printed circuit board 7 is housed in the case 8 and then manufactured by mold casting with the resin material 11 through the opening 9.

Next, the operation of this embodiment will be described in order of the load current characteristic that determines the capacitance condition of the external load, the leakage current characteristic that determines the non-detection condition, and the internal voltage drop characteristic that determines the detection condition.

(1). Load current characteristic An external load and a power source are connected between the signal terminal OUT of the sensor and the common terminal GND, and the pair of PNP type transistors Q1 and Q2 are mirror circuits in the same package, that is, one transistor. When the Darlington connection circuit 3 is turned ON, the Darlington connection circuit 3, the light emitting diode LED, and the mirror circuit of the parallel connection are connected to each other when the current is applied to the other transistor. A drive current flows through the load by the PNP transistors Q1 and Q2 and the resistor R1.

Here, the voltage value between the emitter and base of the PNP type transistors Q1 and Q2 of the mirror circuit configuration is VE.
B, the resistance value of the resistor R1 is R1, the PNP transistor Q
When the current value of the bases of 1 and Q2 is IB, the current IF of the light emitting diode LED is substantially IF = VEB / R1
Since + 2IB and (VEB / R1) >> 2IB, the current IF becomes almost constant.

The base-emitter voltage VB of the PNP transistors Q1 and Q2 is balanced by VEB of the PNP transistor Q1 and VBE of the PNP transistor Q2 + the input impedance RIN of the sensor IC including the bridge circuit 1 and the amplifier 2. It Therefore, even if the load changes, the light emitting diode LED is driven with a constant current.
The load current of the sensor circuit can be increased.

This circuit characteristic gives a measurement result as shown in FIG. 4, for example, which is shown in the graph of FIG.
The current IF flowing through the light emitting diode LED is almost constant with respect to the increase of the load current IL of ˜50 mA, so that the characteristic without load dependency can be confirmed. It is considered that this is because the increase in the load current IL can be completely absorbed by the PNP transistor Q2. Further, the voltage drop of the constant current diode ID when ON is a negligible value of 50 mV or less because the PNP transistor Q1 is ON.

Specifically, when the load current IL flows, the load current IL is shunted to the PNP transistors Q1 and Q2 and the resistor R1 by the input impedance. Of these, the base current is 1 / (hFE + 1) due to the current amplification degree hFE of Q2 in the PNP transistor Q2.
As the collector current, a current of hFE / (hFE + 1) times flows.

At this time, V of the PNP transistor Q2
EB is determined by the IB-VEB characteristic of the transistor. This VBE
Has less current dependency, the current flowing through the resistor R1 is V
It becomes a constant current of EB / R1. On the other hand, the PNP transistor Q1 has an impedance on the sensor IC side of 5 to 6 kΩ.
Since the base current is not the same as that of the PNP transistor Q2 because it is larger than that of the PNP transistor Q2, the PNP transistor Q1 is turned on in a completely saturated state.

With respect to the PNP type transistors Q1 and Q2 having this mirror circuit configuration, since VEB is set to Q1 = Q2, pair transistors are used as Q1 and Q2. However, when VEB is Q1> Q2, there is a problem that Q1 does not reach the saturation region, and when VEB is Q1 <Q2, the current of Q1 becomes large and the current of the light emitting diode LED increases accordingly. Does not have a constant current. From the above, PN
As the P-type transistors Q1 and Q2, it is necessary to use two composite transistors contained in one package.

As a result, the current IF flowing in the light emitting diode LED is determined by the VEB of the PNP type transistors Q1 and Q2 of the mirror circuit configuration in one package and the resistance value of the resistor R1 connected in parallel with it. Since a substantially constant current flows through the light emitting diode LED, a large load current can be taken.

(2) Leakage current characteristic When the sensor IC having the built-in bridge circuit 1 of the MR elements 1a to 1d does not detect, the leakage current of the circuit is determined by the pinch-off current of the constant current diode ID. For example, a constant current is supplied to the sensor IC from the signal terminal OUT through the constant current diode ID via a load from a power supply DC24V connected to the outside.

At this time, the output of the amplifier 2 incorporated in the sensor IC is at the Low level, the NPN type transistors Q3 and Q4 of the Darlington connection circuit 3 are cut off, and the PNP type transistors Q1 and Q2 are also turned off.
The state becomes the FF state. In this case, the leakage current at the time of OFF is determined by the constant current diode ID. For example, the pinch off current of the constant current diode ID has a manufacturer standard value of 0.6.
It is 0 to 0.92 mA, and the leakage current satisfies 1 mAMAX.

The voltage applied to the sensor IC is determined by the leakage current, but the impedance of the sensor IC is the resistance of the MR elements 1a to 1d of the bridge circuit 1 (for example, 6).
(kΩ x 4 elements), so the current consumption is 0.6
It becomes 3.6V in mA, and the working voltage range of the sensor IC (3 ~
30V) is satisfied. The power supply voltage of this sensor IC must always be within that range.

As a result, the leakage current of the two-wire type sensor circuit is determined by the characteristics of the constant current diode ID when no detection is performed. Therefore, for example, a constant current is formed by the forward voltage of the transistor, the resistor, and the light emitting diode, and the leakage current is varied between manufacturing lots. The variation in the leakage current value can be reduced as compared with the case where the variation in the characteristics of each element has a great influence. In particular, a device manufacturer of a constant current diode ID can clearly manage the current value with a single lot-controlled component.
The manufacturing control can be simplified and the yield can be improved.

In addition, PNP type transistors Q1 and Q2
Since it is possible to prevent the dark current from flowing from the base terminal to the NPN transistor Q3, it is possible to surely turn off the light emitting diode LED without the dark current flowing through the light emitting diode LED.

(3). Internal voltage drop characteristics During detection by the sensor IC having the built-in bridge circuit 1 of the MR elements 1a to 1d, the internal voltage drops are VBE of the PNP transistors Q1 and Q2, VCE of the NPN transistor Q4 and light emission. Determined by VF of diode LED.

That is, at the time of detection, the output of the sensor IC becomes the High level, and the NPN type transistors Q3 and Q3.
4 is turned on. Here, the PNP transistor Q from the signal terminal OUT through the load from the power supply DC24V
A base current flows through the NPN transistor Q3 through the emitter terminals of 1 and Q2.

At this time, the PNP type transistors Q1 and Q
The emitter potential of 2 is VA = (VEB of PNP type transistors Q1 and Q2) +
It is determined by (VF of light emitting diode LED) + (VCE of NPN transistor Q4), and this becomes the internal voltage drop.

Here, (V of NPN transistor Q4
CE) = (VCE of NPN transistor Q3) + (resistance R
3 voltage drop) + (VBE of NPN transistor Q4)
And (VCE of NPN transistor Q3) + (NP
Since VBE of N-type transistor Q4) >> (voltage drop of resistor R3), VA = (VEB of PNP-type transistors Q1 and Q2) +
(VF of light emitting diode LED) + (VCE of NPN transistor Q3) + (VB of NPN transistor Q4)
It can also be expressed as E).

At this time, the power supply voltage of the sensor IC is also PN
Since the P-type transistors Q1 and Q2 are in the ON state, they become almost equal to the internal voltage drop. With respect to this internal voltage drop, when the design value is calculated with reference to the standard table, the operating voltage range of the sensor IC is satisfied.

As a result, at the time of detection, the residual voltage is determined by the VBE of the PNP transistors Q1 and Q2, the forward voltage of the light emitting diode LED, and the VCE of the NPN transistor Q4, so that the voltage drop can be corrected to stabilize the operation. it can.

Moreover, since the output impedance on the side of the amplifier 2 can be increased by the Darlington connection circuit 3, the voltage at the time of detection can be stabilized for operation. That is, in the 2-wire type sensor circuit, the circuit current is 0.8 mA.
In order to suppress it to a certain degree, it is necessary to configure the inside of the sensor IC with a high impedance circuit, the output impedance on the amplifier 2 side becomes high, and one stage of the transistor cannot be driven. Therefore, it is an important element to configure with the Darlington connection circuit 3. Become. Further, the threshold value (threshold level) can be raised by the Darlington connection circuit 3, and the matching with the output of the operational amplifier becomes good.

Therefore, according to the two-wire type sensor circuit of this embodiment, the Darlington connection circuit 3, the light emitting diode LED, and the PN of the mirror circuit configuration connected in parallel are connected to the sensor IC.
By connecting the P-type transistors Q1 and Q2, the resistor R1, the constant current diode ID, etc., in the load current characteristics, even if the external load changes, a substantially constant current flows in the light emitting diode LED, and constant current driving is performed. So
It can take a large load current as a sensor circuit,
Therefore, it can be applied to a load having a large capacity such as a relay. Furthermore, even if the load current changes significantly, a substantially constant current flows through the light emitting diode LED,
The stability of the internal voltage drop is improved, and the matching with the load is improved.

Regarding the leakage current characteristic, when it is not detected, the leakage current is determined only by the characteristic of the constant current diode ID, so that the variation of the leakage current value can be reduced and the dark current to the NPN transistor Q4 can be reduced. Does not flow, the light emitting diode LED can be reliably turned off.

Further, in the internal voltage drop characteristic, since the voltage is determined by the PNP type transistors Q1 and Q2, the light emitting diode LED and the NPN type transistor Q4 at the time of detection, it is possible to stabilize and operate the voltage, and Darlington. The connection circuit 3 can be a general-purpose component for increasing the output impedance, and can be configured with a minimum number of components.

In the sensor structure, when the printed board 7 is housed in the case 8, after being housed through the opening 9 provided in the direction opposite to the lead wire grommet portion 10,
Since the resin material 11 can be assembled from the opening 9 by molding, the sensor can be easily assembled, and the lead wire grommet portion 10 is molded and molded, and the lead wire is resistant to bending and water. Can be improved.

Although the invention made by the inventor has been specifically described based on the embodiments of the present invention, the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the scope of the invention. Needless to say, it can be changed.

For example, as for the two-wire type sensor circuit of the above-mentioned embodiment, a case where the sensor circuit is mounted by assembling only by mold casting from the opening 9 of the case 8 with the resin material 11 will be described. However, the present invention is not limited to the above-described embodiment, and various modifications can be made to the sensor structure, such as when the lid 12 is provided in the opening 9 of the case 8 as shown in FIG. In particular, this mold makes it possible to improve the bending resistance and water resistance of the lead wire grommet portion 10.

In the circuit configuration, the case where the capacitor C for external noise countermeasures and the constant voltage diode D for surge voltage countermeasures are connected between the terminals of the sensor IC has been described. When used in an environment in which no occurrence of these occurs, these countermeasure parts are unnecessary.

In the above description, the invention mainly made by the inventor is the cylinder 5 to which the invention belongs.
The case where the present invention is applied to a two-wire type sensor circuit used for position detection has been described, but the present invention is not limited to this, and a position detection device for other fluid pressure operated equipment such as a rotary actuator and a detection function are required. It is also widely applicable as a sensor circuit for other devices.

[0058]

Advantageous effects obtained by typical ones of the inventions disclosed in the present application will be briefly described.
It is as follows.

(1). By connecting a Darlington connection circuit, a light emitting diode, a pair of transistors and a resistance element having a mirror circuit configuration connected in parallel, and a constant current diode to the output stage of the sensor circuit, the capacitance of the external load is increased. In the load current characteristic that determines the condition, the load current that determines the capacity of the load can be made large by making the current flowing through the light emitting diode almost constant.
By expanding the load applied to relays, etc., it becomes possible to improve versatility from small capacity to large capacity.

(2). In the leakage current characteristic that determines the non-detection condition, since the leakage current is determined by the constant current diode, it is possible to reduce the variation in the current value by controlling the characteristic of this constant current diode, and Since dark current does not flow from the transistor of the mirror circuit configuration to the Darlington connection circuit, it is possible to stabilize on the circuit and prevent the current from flowing completely to the light emitting diode, so it is possible to turn off the light emitting diode without fail. .

(3) In the internal voltage drop characteristics that determine the detection conditions, the output voltage of the detection signal is the base-emitter terminal voltage of the transistor, the light-emitting diode forward voltage, and the collector-emitter terminal voltage of the Darlington connection circuit. Since the current of the light emitting diode is almost constant, the voltage drop can be compensated for the change of the load current, and stable operation in the optimum state becomes possible. Furthermore, by using the Darlington connection circuit, the amplifier side Since the output impedance can be increased and the threshold value can be increased, the operation of the sensor circuit can be stabilized.

(4). A sensor structure using a two-wire type sensor circuit can be manufactured by housing a printed circuit board on which the sensor circuit is mounted in a case, and then performing mold casting from the opening of the case. Therefore, it is possible to simplify the assembly by the mold casting, and since the mold is cast even to the lead wire grommet portion, it is possible to improve the environmental resistance such as bending resistance and water resistance.

(5). A small number of general-purpose SMD parts, which are about the same number as the number of conventional parts, make it possible to construct a circuit with good performance. Can be realized.

(6). By using general-purpose SMD parts,
The development cost of the IC is reduced to reduce the development cost. Since it is a general-purpose product, it is easy to obtain and the characteristics are controlled, so it is possible to reduce the number of development days. Since there are almost no factors, it is possible to improve the manufacturing yield and obtain a two-wire sensor circuit in which the quality can be easily stabilized.

(7) Especially, by using the two-wire type sensor circuit for the position detection of the fluid pressure operating device, it is possible to obtain the position detection device capable of highly reliable position detection by the stable operation of the sensor circuit. it can.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a two-wire sensor circuit according to an embodiment of the present invention.

2 (a) and 2 (b) are a front view and a side view showing a state in which a sensor using the two-wire type sensor circuit of the present embodiment is mounted on a fluid pressure operating device.

FIG. 3 is a sectional view showing an example of a sensor structure according to the present embodiment.

FIG. 4 is an explanatory diagram showing load current characteristics in the present embodiment.

FIG. 5 is a characteristic diagram showing a load current characteristic in the present embodiment.

FIG. 6 is a cross-sectional view showing a modified example of the sensor structure according to the present embodiment.

FIG. 7 is a circuit diagram showing a two-wire sensor circuit which is a comparative example of the present embodiment.

FIG. 8 is a sectional view showing an example of a sensor structure in a comparative example of the present embodiment.

[Explanation of symbols]

 1 bridge circuit 1a to 1d MR element (detection element) 2 amplifier 3 Darlington connection circuit 4 position detection device 5 cylinder (fluid pressure operation device) 6 mounting groove 7 printed circuit board 8, 8a case 9 opening 10 and 10a lead wire grommet part 11, 11a Resin material 12 Lid C Capacitor D Constant voltage diode GND Common terminal IC sensor ID Constant current diode LED Light emitting diode OUT Signal terminal Q1, Q2 PNP transistor Q3, Q4 NPN transistor R1 to R6 Resistance

Claims (2)

[Claims] 1. Used for position detection of a fluid pressure operated device,
A two-wire sensor circuit having a signal terminal for outputting a detection signal from a bridge circuit by a detection element through an amplifier and a common terminal, the Darlington connection circuit having a base terminal connected to the output terminal of the amplifier, A light emitting diode whose cathode terminal is connected to the collector terminal of this Darlington connection circuit, and a first transistor and a second transistor having a mirror circuit configuration in which a base terminal is connected to the anode terminal of this light emitting diode and one end are connected A first element and a second transistor having the mirror circuit configuration, each including a resistance element and a constant current diode connected between the emitter and collector terminals of the first transistor in a forward direction from the emitter terminal to the collector terminal. Other than the emitter terminal and the resistance element There is connected to the signal terminal, two-wire sensor circuit emitter and collector terminals of said second transistor is characterized in that it is connected to the common terminal of the Darlington connection circuit. 2. A sensor structure using the two-wire type sensor circuit according to claim 1, wherein the first structure has the mirror circuit configuration.
And the second transistor are built in the same package, and the two-wire sensor circuit is mounted on a printed circuit board, and an opening of a case for accommodating the printed circuit board is formed on the printed circuit board. A sensor structure, which is provided in a direction opposite to a lead wire grommet portion for external connection to be connected, and is manufactured by being mold-molded from the opening after the printed circuit board is housed in the case.