JPS59212026A - Oscillation circuit for proximity switch - Google Patents

Abstract

PURPOSE:To perform temperature compensation at a specific rate of currents flowing through a couple of transistors (TR) regardless of the sensitivity adjustment resistance value of an oscillation circuit by providing a temperature compensating resistance which varies said current ratio according to temperature. CONSTITUTION:The proximity switch consists of a sensor 1, oscillation circuit 4, detecting circuit 5, level discriminating circuit 6, output circuit 7, and constant-voltage circuit 8, and TRs 2 and 3 of the oscillation circuit 4 constitute a current mirror circuit. The emitter of the TR2 is connected to the output of the constant-voltage circuit 8 through a resistance R2, and the emitter of the TR3 is connected through a resistance R3 and a temperature compensating resistance (e.g. linear positive temperature coefficient resistance) RT1 having a positive temperature coefficient, so the temperature compensation is carried out at the specific rate regardless of the sensitivity adjustment resistance value R1+VR1.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of the Invention The present invention relates to an oscillation circuit for a proximity switch used for object detection and the like.

ρ) Background of the Invention A proximity switch includes an oscillation circuit including a detection coil 9
Normally, this oscillation circuit is left in oscillation.

When an object approaches the detection coil for a predetermined distance or more, the conductance of the 9 oscillation circuit changes so that the amplitude of one oscillation decreases or stops, and this decrease in oscillation amplitude or stoppage of oscillation is extracted by level discrimination. There is one based on the principle of detecting the proximity of. In the oscillation circuit of this rice proximity switch, the various constants of the circuit change due to temperature changes, and therefore the conductance also changes, so the detection accuracy also changes depending on the temperature. Therefore, it is necessary to perform temperature compensation on the 9 oscillation circuit. This temperature compensation is not possible in conventional proximity switches where the detection coil and oscillation circuit are integrally formed.

A temperature compensation resistor may be connected in series with the sensitivity adjustment resistor provided in the oscillation circuit. Once the sensitivity is fixed,
It is sufficient to compensate for the change in sensitivity to temperature change by inversely changing it using a temperature compensation resistor.

However, in the so-called amplifier-separated type proximity switch that has been developed in recent years, the sensor section including the detection coil and the circuit section including the main part of the oscillation circuit are configured separately and the two are connected by a cable.

In the method of connecting a temperature compensation resistor in series with a sensitivity adjustment resistor, proper temperature compensation cannot be performed for the following reasons. With amplifier-separated proximity switches, depending on the purpose,
Various sensors are attached to the circuit section.

They are connected interchangeably, but if a different sensor is connected, the conductance of the detection coil inside the sensor will also be different, so the sensitivity must be adjusted using the sensitivity adjustment resistor in the excavation circuit of the 2nd circuit section in response to the connection of different sensors. will be carried out. This T
Since the resistance value of the sensitivity adjustment resistor is different for each sensor connected, even if a temperature compensation resistor is connected to the sensitivity adjustment resistor circuit, the compensation of the temperature compensation resistor for the sensitivity will vary. - It is not possible to provide reasonable compensation.

(c) Purpose of the Invention In view of the above, the purpose of the present invention is to maintain a constant value, regardless of the value of the conductance of the detection coil, and therefore, regardless of the value of the sensitivity adjustment resistance of the oscillation circuit. An object of the present invention is to provide an oscillation circuit for a proximity switch that is temperature compensated by the ratio.

B) Structure and Effect of the Invention To achieve the above objects, the oscillation circuit of the proximity switch of the present invention uses a current mirror circuit, that is, a first transistor connected as an emitter follower, and a second transistor connected as an emitter follower. and a current mirror circuit including a sixth transistor, the second transistor is connected in series with the first transistor, and a third transistor feeds back the output current of the first transistor; A current mirror circuit is connected to an oscillation circuit including a parallel resonant circuit consisting of a detection coil and a capacitor to which a feedback current is applied, and a T-column circuit that supplies a base current of the first transistor. A temperature compensating resistor is provided to change the ratio of current flowing through the sixth transistor depending on the temperature.

According to the oscillation circuit of the proximity switch of this invention.

Oscillation direction ll! A temperature compensation resistor is provided in the current mirror (b) constituting 1!1, and when the gain of the circuit changes due to temperature change, the resistance value of the temperature compensation resistor changes to cancel this change, and the current mirror circuit Since it changes the ratio of current flowing through a pair of transistors, that is, the optical feedback ratio, no matter what is connected to the detection coil and the sensitivity adjustment resistor is set to a value such as Temperature compensation can be made.

(e) Description of Embodiments The present invention will be explained in further detail with reference to embodiments shown in the following nine drawings.

FIG. 1 is a circuit diagram of a proximity switch showing one embodiment of the present invention. The proximity switch shown in the figure is composed of a sensor 1 containing a detection coil L, and a circuit section 3 to which the sensor 1 is connected via a cable 2. In other words, this proximity switch.

This is a so-called amplifier separated type in which the sensor 1 and the circuit section 5 are configured separately. The circuit section 6 includes 9 oscillation circuits 4 and a detection circuit 5 that receives the oscillation output of the oscillation circuit 4 and detects the wave. Detection circuit 5
Level discrimination circuit receives the output of and compares it with a reference signal level 6. It is comprised of an output circuit 7 which receives the output of the level discrimination circuit 6 and outputs an on/off signal indicating the presence or absence of an object in the vicinity, and a constant voltage circuit 8 which supplies a constant power supply correction to each circuit. Note that 9 is the power supply end, and 10 is the output end.

11 is a common end. The basic configuration of the T-coupler described above is not unique to this embodiment, but is well known as a high frequency oscillation type proximity switch. The invention of this application relates to an oscillation circuit, and since the characteristic part of the proximity switch shown here is the oscillation circuit 4, the internal circuit connections of the oscillation circuit 4 will be further explained and explained. The oscillation circuit 4 is an fJ-current feedback type oscillation circuit including a resonant circuit from a detection coil L connected to a capacitor C via a cable 2. The emitter of the transistor TR1 (first transistor) of this oscillation circuit 4 is a resistor) tl, the sensitivity adjustment volume V
li1. >Connect to the common end 11 through the transistor Tl, that is, the emitter follower connection.
The collector of t1 is a pair of transistors pT 142 ,
The commonly connected base of T R3 (second and fifth transistors) is connected to the collector of transistor T It 2. The transistor 'ra2゜1'R3 constitutes a current mirror 1, and the emitter of the transistor TR7 is connected to the trench T through the resistor R2. They are each connected to the output of the constant voltage circuit 8, i.e. 'c), to the power supply V via a compensation resistor (one word near positive temperature coefficient resistor) It'rt. To ζ et al.

The collector of the transistor TR3 is connected to the signal output terminal A of the resonant circuit consisting of the detection coil L and the capacitor 10.

A series connection circuit including a transistor TR4, resistors R4 and R5, and a volume VR2 for adding hysteresis is connected. The emitter of the transistor TR4 is connected to the base of the transistor TR8 of the detection circuit 5, and the detection circuit 5 is connected to the oscillation circuit 40.
The 011 resistor R to which the oscillation output is supplied
The connection terminal between Tyt4 and Tyt5 is connected to the base of transistor Tyt1, and the emitter voltage of transistor Tyt4 is divided by resistor R4, resistor R5, and volume VR2, and is supplied to the base of transistor Tyt1. ing. A transistor TR7 is connected between the center terminal of the hysteresis volume VR2 and the common terminal 11, and a transistor TR7F
! ! By turning it on, hysteresis is added. Transistor TR7 can be turned on and off in response to a signal from level discrimination circuit 6.

A resistor R6 is connected between the base and collector of the transistor TR4 in order to allow an appropriate current to flow through the transistor TR4.1. Between the base of the transistor TI't4 and the connection point A of the resonant circuit, the transistor T R5s T Rb
A series circuit includes a Darlington connection and a resistor R7, and an AC bypass capacitor C1 is connected in parallel to this series circuit.

Next, regarding the operation of the oscillation circuit 4 configured to be connected as described above, first, the general operation when no temperature compensation resistor is connected to the current mirror circuit will be described.

The output current IF flowing through the transistor TR1 is.

First, it is determined by the sensitivity adjustment resistor R1+■1 connected to the emitter. Corresponding to this output current IF, a current IA also flows through the transistor TR2 of the current mirror circuit, and the base of each of the transistors TR2 and TR3 of the current mirror circuit also flows. Since the voltages applied between and the power supply 7 are equal and the resistor R2 = R3, a current IB of 1:1 flows through the transistor TR3 in response to the current IA flowing through the transistor TR2.
This current is supplied to the resonant circuit. That is, the output current I
F will be fed back to the resonant circuit.

On the other hand, the base of transistor TR4 is connected to resistor R6.
A bias voltage determined by the forward voltage between the bases and emitters of the transistors TR5 and TR6 and the resistor R7 is applied, so that a bias current flows through the transistor TR4. Therefore, current also flows through the resistors R4 and R5 and the volume VR2, and the emitter voltage of the transistor TR4 is distributed between the resistors R4 and R5 and the volume VR2.

A bias voltage is applied to the base of transistor TR1. Even with this bias voltage, the transistor TR1
output current is affected.

For example, if the power is turned on and the voltage across the detection capacitor L, that is, the voltage at the connection point A of the resonant circuit increases, this causes the base potential of the transistor TR4 to also increase in an alternating current manner. Correspondingly, the potential on the emitter side of the transistor TR4 also increases slightly. Due to this rise, the voltage applied to the base of the transistor TRi also rises, and therefore the potential of the emitter of the transistor TR1 also rises, and the current I flowing through the resistor R1 and the volume VR1 increases.
F becomes large. Therefore, the current IA flowing between the emitter and collector of the transistor TR2 increases.

Therefore, the current IB flowing between the emitter and collector of the transistor TR, which corresponds 1:1 to the current IA, also increases. This current IR is then fed back to the resonant circuit. In this way, when the terminal voltage of the resonant circuit increases, positive feedback is applied as an increased current IB. Therefore, the oscillation continues to grow from then on.

As shown in Figure 1, the transistor T of the current mirror circuit
A temperature compensation resistor R is connected to the resistor R3 connected to the emitter of R3.
When T1 is connected, the transistor TR of the current mirror circuit
The voltages between the bases of TR2 and TR3 and the power supply 7 are both equal and can be expressed by a 9th order equation.

R2, IA-4-VF'2=(R3+RT1)IB+V
F3-(1) However, VF2: Base-emitter voltage of transistor TR2.

vF'3:) Base-emitter voltage of transistor TR3.

Here, VF 2 = VF3 is used, so the above formula %
Formula % (2) Generally, as the temperature rises, the gain of the transistor changes in an upward direction. When the gain of the transistor increases, the oscillation amplitude of the oscillation circuit 4 becomes larger than normal. The fact that the oscillation amplitude of the oscillation circuit 4 is large, that is, the oscillation intensity is large, means that a detection output cannot be obtained unless the object comes closer than usual, and therefore the detection distance becomes small. Therefore, when the temperature rises, it is preferable to make the feedback from the current mirror circuit smaller than in normal times in order to compensate for this. In the above equation (2), in order to reduce the feedback current IB, if R2·IA is constant, the resistance (R3+RT1) may be made large. Do not increase the resistance (R3+RT1).

A resistor having a positive temperature coefficient may be used as the temperature compensating resistor RT1. If the temperature compensation resistor RT1 with a positive temperature coefficient is connected to the emitter of the transistor TR3 in this way, even if the gain of each transistor increases due to temperature rise, the resistance value RTI will also increase and the feedback current IB will decrease. So, //! It is possible to compensate for the deterioration of the detection distance due to the degree of deterioration.

Note that in order to suppress the influence of transistor gain changes due to temperature changes, it is sufficient to change the ratio of the feedback current to the resonant circuit, so instead of the current mirror circuit of the embodiment shown in FIG. Transistor TR2 as shown in the figure
A temperature compensation resistor RT2 may be connected to the emitter side of the resistor RT2.

In this case.

(R2+RT2) IA=R3 fist IB Since the formula holds true, how to reduce IB/IA.

R2+RT2 can be made small. Therefore, as the temperature compensating resistor RT2, a resistor whose resistance value decreases as the temperature rises, that is, a resistor having a negative temperature coefficient may be used. There are thermistors and the like that have a negative temperature coefficient, but when using a temperature compensation resistor that has a negative temperature coefficient, the negative /l! Resistance R with variable coefficient
Two ordinary resistors i'm''R are connected in parallel to Tn as shown in Fig. 3, and this parallel gate circuit is connected between the emitter of the transistor TR2 of the above current mirror circuit and the resistor R2. Good too.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a proximity switch in which the present invention is implemented, Fig. 2 is a connection diagram showing another current mirror circuit applied to the above-mentioned proximity switch, and Fig. 3 is a temperature compensation having a negative temperature coefficient. It is a connection diagram for ensuring linearity of resistance. 4: Oscillation circuit. TR1: first transistor. TR2: second transistor. TR3: third transistor. L: detection coil, C: resonance capacitor. RTl: Temperature compensated resistor with positive temperature coefficient. RT2: Temperature compensated resistor with negative temperature coefficient. Patent applicant: Tateishi Electric Co., Ltd. Representative Patent attorney: Shigeru Nakamura (14)

Claims (3)

[Claims] (1) A first transistor connected as an emitter follower, and second and sixth transistors, the second transistor being connected in series with the first transistor, and the sixth transistor being connected in series with the first transistor;
a current mirror circuit in which the transistor feeds back the output current of the first transistor; a parallel resonant circuit consisting of a detection coil and a capacitor to which the feedback current from the third transistor is applied; and a base current of the first transistor. In a proximity switch oscillator circuit including a supply reservoir circuit. An oscillation circuit for a proximity switch, characterized in that the current mirror circuit is provided with a temperature compensation resistor that changes the ratio of current flowing through the second and third transistors depending on the temperature. (2) The oscillation circuit for a proximity switch according to claim 1, wherein the temperature compensation resistor has a positive temperature coefficient and is connected in series with the third transistor. (3) The proximity switch according to claim 1, wherein the temperature compensation resistor has a negative temperature coefficient and is connected in series with the second transistor.