JPS604868A - Sensor circuit - Google Patents

Abstract

PURPOSE:To make it possible to prevent the damage of electronic equipment by certainly generating an alarm signal even if there is cable pulling-off or contact inferiority, by providing a transistor to a sensor detection circuit while inserting a resistor in series with respect to a sensor. CONSTITUTION:If the resistance value of a temp. sensor 1 is lowered by the rising in temp. and a resistance value Ri becomes small, voltage V1 is contrarily rises. When V1 reaches a certain value or more, a comparator circuit 10 is operated to generate an alarm signal. Therefore, when cable is not connected by mistake and so called cable pulling-off is generated, V1=Vcc is formed and the generation of abnormality is judged to issue the alarm signal. In addition, even when the connection of the cable is bad and contact inferiority is generated, V1 becomes high in the same way as the reduction in the resistance value R1 of the temp. sensor 1 and, if the operation condition of the comparator circuit 10 is set to a certain value, abnormality is judged to enable the generation of the alarm signal.

Description

[Detailed description of the invention] fat Technical field of invention The present invention relates to sensor circuits.

(bl Technology background) In recent years, with the expansion of the functions of electronic devices, various functions have been added and their control systems have been automated, and with the development of high-quality sensors, sensors are often incorporated into control systems. The number is increasing.

Monitors abnormalities in physical phenomena within the power supply control system and main processing equipment of electronic equipment, detects any abnormality, sends an abnormality alarm signal, and prevents destruction due to abnormalities in physical phenomena. A variety of sensors have been developed that serve to protect electronic devices from

Among various sensors, temperature sensors that detect the surface temperature inside devices and electronic components are commonly used, but there are also optical sensors that detect the position of objects and other sensors that detect changes in physical phenomena electrically. A conversion and control method has been developed, and the spread of automated monitoring functions using sensors has been remarkable, replacing human monitoring functions. Even with these high-quality sensors, if there is a malfunction in the peripheral circuitry and a situation occurs in which an abnormality is not detected, the damage incurred will be enormous and there is a fear that it will affect a wide variety of fields.

(C1 Prior Art and Problems The conventional detection circuit of this type of general sensor will be explained. Figure 1 shows a block diagram of the circuit configuration of the conventional sensor detection circuit. In this circuit configuration, the sensor changes resistance. This is explained as a temperature sensor 1 with a negative characteristic that the resistance value decreases as the temperature rises. 2 and 3 are cables that connect the temperature sensor 1 and the detection circuit. Voltage is supplied from the input power supply VCC through the resistor 4. The output of the cable 2 on one side to which is applied is connected to the comparator circuit 5, and the output of the cable 3 on the other side is grounded. is lower than the reference potential 6, an alarm signal is sent from the signal terminal 7 and connected to an alarm circuit (not shown).

Considering the case where an alarm signal is generated when the temperature exceeds a certain temperature To, the resistance value of the temperature sensor 1 is Ro, the resistance value of the resistor 4 is Rf, the voltage at the input terminal of the comparator circuit 5, that is, the output of the cable 2 is vl, If the voltage of the power supply is Vcc, when Vl > (Ro/Ro+Rf) Vcc, normal when Vl < (Ro/Ro+Rf) Vcc
It becomes normal when the abnormal cable is disconnected (Vl = Vcc). That is, in the conventional detection circuit, the resistance value of the temperature sensor 1 decreases as the temperature rises, Ro decreases, and vl
When the value decreases to below a certain value, the comparison circuit 5 operates and generates an alarm signal. However, if the cable is not connected by mistake, a so-called cable disconnection phenomenon, the vl
It had a serious drawback that V1=Vcc without decreasing, and the phenomenon of cable disconnection was judged as normal.

(dl OBJECT OF THE INVENTION The present invention aims to solve this conventional drawback.

te+ Structure of the Invention The above object is to provide a comparison circuit including a reference voltage input terminal and a voltage to be measured input terminal, and a sensor whose one end is connected to the voltage to be measured input terminal via a series resistor and the other end is grounded. and a transistor whose collector is connected to the voltage input terminal to be measured, whose emitter is grounded, and whose base is connected to the connection point between the series resistor and the sensor. achieved.

In other words, by using changes in the voltage between the base and emitter of the transistor, which is the voltage across the temperature sensor, as the resistance value of the temperature sensor decreases, the output voltage of the sensor circuit increases and exceeds a certain set value. This circuit is configured to generate an alarm signal when the cable is disconnected, and to provide a circuit that reliably generates an alarm signal even in the event of cable disconnection or poor contact due to poor connection.

(fl Embodiment of the Invention An embodiment of the present invention will be described below. FIG. 2 shows a circuit configuration block diagram of a sensor detection circuit according to the present invention. In this figure, the same objects are designated by the same symbols as in FIG. 1. 8 is a resistor connected in series with the temperature sensor 1, 9 is a transistor provided at the input end of the sensor circuit, 10 is a comparison circuit, and 11 is a reference potential of the comparison circuit 10.The collector of the transistor 9 is connected to the cable 2 side. , the emitter is connected to the cable 3 side, and the base is connected to the connection point between the temperature sensor 1 and the resistor 8.The comparator circuit 10 connects when the potential at the input end applied via the cable 2 is higher than the reference potential 11. It is configured to send out an alarm signal from the signal terminal 7 when the alarm occurs.

In this figure, considering the case where an alarm signal is generated when the temperature exceeds a certain temperature To, the resistance value of temperature sensor 1 is set to R.
o, the resistance value of the resistor 8 is Ri, the voltage at the input terminal of the comparator circuit 10 is vl, and the voltage between the base and emitter of the transistor 9 is VBB, then Vl-(1+Ri/Ro) VBE, and Vl > (1+Ri/ Ro) When VBE, abnormal Vl < (1+Ri/Ro) When VBE, normal cable disconnection (Vl = Vcc) An abnormality occurs. That is, in the detection circuit according to the present invention, the resistance value of the temperature sensor l decreases as the temperature rises, and R.

Conversely, when vl becomes smaller, vl increases, and when it exceeds a certain value, comparator circuit 5 operates and generates an alarm signal. Therefore, if the cable is not connected by mistake, so-called cable is disconnected, V1=Vcc, and it is determined that there is field lightning and an alarm signal is generated.

Furthermore, even if the cable is poorly connected and there is a contact failure, vl increases in the same way as the resistance value Ro of the temperature sensor 1 decreases, and if the operating conditions of the comparator circuit 10 are set to a certain value, an alarm signal is issued as an abnormality. can be generated.

In the present invention, a case has been described in which a temperature sensor with a negative characteristic becomes abnormal when the temperature becomes high, but the same applies to a case where a temperature sensor with a positive characteristic becomes abnormal when the temperature becomes low.

(gl As explained in detail about the invention, by providing a transistor in the sensor detection circuit and inserting a resistor in series with the sensor, an alarm signal can be reliably generated even if the cable is disconnected or there is a poor connection.) This has the effect of preventing damage to electronic equipment.

[Brief explanation of the drawing]

FIG. 1 shows a circuit configuration block diagram of a conventional sensor detection circuit, and FIG. 2 shows a circuit configuration block diagram of a sensor detection circuit according to the present invention. In the drawing, 1 is the temperature sensor number, 12 and 3 are the cables,
8 is a resistor, 9 is a transistor, 10 is a comparison circuit, and 11 is a reference potential.

Claims (1)

[Claims] a comparison circuit including a reference voltage input terminal and a voltage to be measured input terminal; a sensor having one end connected to the voltage to be measured input terminal via a series resistor and the other end being grounded;
Its collector is connected to the voltage input terminal to be measured,
A sensor circuit comprising a transistor whose emitter is grounded and whose base is connected to a connection point between the series resistor and the sensor.