JPH0332029B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a reflective photoelectric switch that irradiates a light beam onto an object to be detected using a projector and receives the diffusely reflected light with a receiver to detect the presence or absence of the object to be detected. It is related to.

[Background Art] As shown in FIG. 2, a reflective photoelectric switch receives diffusely reflected light from the surface of an object with a light receiving element 2, and
After converting into a voltage signal in the light receiving circuit 3, logarithmic conversion is performed in the logarithmic amplifier circuit 4, and this output Vin is inputted to the object detection comparison circuit 5 and compared with the detection level setting voltage Vs for adjusting the sensitivity. When Vin is larger, a detection signal is output. Signal processing circuit 10
In this case, external light noise is removed by sampling the output of the comparison circuit 5 at the pulse timing when the light beam is generated from the projector, and the output of this signal processing circuit 10 is used as the output for driving the relay and indicator lamp. It is added to circuit 6. The logarithmic amplifier circuit 4 uses an operational amplifier G and a feedback diode D to perform logarithmic conversion of the received light signal output, thereby making the distance to the object proportional to the detection signal level, expanding the dynamic range, and achieving highly accurate detection. This is what makes it possible. Conventionally, this signal was input to the comparator circuit 5 and compared with the reference voltage Vs set by the resistors Ra and Rb.
The logarithmic amplifier circuit 4 utilizes the logarithmic characteristics of a silicon diode, and its temperature characteristics depend on changes in carrier concentration due to changes in the temperature of the PN junction. It is impossible to provide the same temperature characteristics as the logarithmic amplifier circuit 4 by using a temperature sensing element such as a thermistor, and there is no suitable temperature compensation method.

Therefore, the present inventors proposed a temperature compensation method as shown in FIG. 3a in Japanese Patent Application No. 58-76818. In the figure, the output of a variable resistor 7 for setting a reference voltage is amplified by a second logarithmic amplifier circuit 9 to become a reference voltage Vs. With this configuration, the first
The temperature drift of the second logarithmic amplifier circuit 4 is offset by the temperature drift of the second logarithmic amplifier circuit 9 and corrected appropriately, but on the other hand, the rotational operation amount of the reference voltage setting variable resistor 7 can be detected. The relationship with distance becomes non-linear, and as shown in Figure b, the farther the distance, the larger the change in distance Δl for a slight change in rotation angle Δθ, making it difficult to set with high precision. Ta.

[Object of the Invention] The present invention has been made in view of the above-mentioned problems, and its purpose is to be able to perform appropriate temperature compensation for a logarithmic amplifier circuit, and to
To provide a photoelectric switch whose sensitivity setting variable resistor can be easily set.

[Disclosure of the Invention] The present invention provides a logarithmic amplifier circuit that logarithmically converts the output of a receiving element disposed on a light-converging surface of a light-receiving optical system, and a comparison circuit that compares and discriminates the output of the logarithmic amplifier circuit with a reference voltage. In a photoelectric switch equipped with
An exponential amplifier circuit that exponentially converts the output of the reference voltage setting variable resistor and a second logarithmic amplifier circuit that logarithmically converts the output of the exponential amplifier circuit are provided, and the output of the second logarithmic amplifier circuit is converted to the output of the comparison circuit. The feature is that the reference voltage is used as a reference voltage, and the reference voltage setting input, which is unavoidably logarithmically converted via a second logarithmic amplifier circuit for temperature compensation, is inversely converted in advance. By doing so, the relationship between the rotational operation angle of the variable resistor and the detection limit distance is kept linear.

FIG. 1a shows an embodiment of the present invention, in which the output current of a light-receiving element 2 disposed on the light-converging surface of a light-receiving optical system 1 is amplified and converted into a signal voltage by a light-receiving circuit 3, and then a logarithmic amplifier circuit 4 performs logarithmic conversion, and logarithmic amplification circuit 4
The output Vin is compared with the reference voltage Vs by a comparator circuit 5, and the output is input to an output circuit 6 comprising a load control relay or the like. Further, the output of the reference voltage setting variable resistor 7 is exponentially converted in an exponential amplifier circuit 8, and then logarithmically converted in a second logarithmic amplifier circuit 9, and the output of this logarithmic amplifier circuit 9 is the reference voltage Vs.
It is input to the comparator circuit 5 as . With this configuration, as shown in Figure b, the variable resistor 7
The rotation angle of the rotation angle and the detection limit distance set thereby can be made approximately proportional.

[Effects of the Invention] As described above, the present invention sets the reference voltage setting input to the second level in order to compensate for the temperature of the logarithmically amplified output of the received light signal.
By passing it through the logarithmic amplifier circuit and inversely converting the setting input in advance, the relationship between the rotary operation angle of the variable resistor and the setting sensitivity is maintained linearly. In addition to being able to perform appropriate temperature compensation, the reference voltage setting variable resistor can be easily set.

[Brief explanation of drawings]

FIG. 1a is a block circuit diagram showing an embodiment of the present invention, FIG. 1b is an operational characteristic diagram of the same as above, FIG. 2 is a block circuit diagram showing a conventional example, and FIG. The block circuit diagram, FIG.

Claims (1)

[Claims] 1. In a photoelectric switch equipped with a logarithmic amplifier circuit that logarithmically converts the output of the light receiving element disposed on the light collecting surface of the light receiving optical system, and a comparison circuit that compares and discriminates the output of the logarithmic amplifier circuit with a reference voltage, the reference voltage an exponential amplifier circuit that exponentially converts the output of the setting variable resistor;
A photoelectric switch comprising: a second logarithmic amplifier circuit for logarithmically converting the output of the exponential amplifier circuit; and the output of the second logarithmic amplifier circuit is used as a reference voltage of the comparison circuit.