JP2509090Y2 - Heat sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a heat detector that detects a temperature rise due to a fire by using a temperature sensitive element such as a thermistor.

[Prior Art] In the conventional heat detector, a constant temperature type heat detector that detects the arrival at a predetermined temperature and outputs a fire signal, and a detector that detects that the temperature rise rate has reached a predetermined value Two types of differential heat detectors that output a fire signal are known.

On the other hand, as a recent heat sensor, a so-called semiconductor heat sensor using a temperature sensitive element such as a thermistor whose resistance value changes with a change in temperature has been put into practical use.

This semiconductor type heat sensor also has a constant temperature type that detects when the resistance value of the temperature sensing element reaches a predetermined value and the rate of change of the resistance value of the temperature sensing element reaches a predetermined value. There is a differential type that detects that a predetermined temperature rise rate has been obtained by doing so, and in order to improve the detection performance, a composite type thermal sensor equipped with both constant temperature type and differential type detection functions. Has been put to practical use.

[Problems to be Solved by the Invention] However, in such a conventional semiconductor thermal sensor, a temperature sensitive element and a determination circuit are separately provided for each of the constant temperature type and the differential type, or the temperature sensing element and the determination circuit are separately provided. Even if the temperature element is the same, the judgment circuit is individually provided, and there is a problem that the number of parts increases and the cost increases.

The present invention has been made in view of such conventional problems, and an object thereof is to provide a heat sensor capable of realizing both constant temperature type and differential type detection functions with the same temperature sensitive element and determination circuit. And

[Means for Solving the Problems] The present invention which achieves this object is configured as follows. The numbers in the drawings of the embodiments are also shown.

First, the present invention provides a constant temperature method for detecting that the temperature of the temperature sensing element reaches a predetermined value, and a predetermined value when the rate of change of the resistance value of the temperature sensing element reaches a predetermined value. The present invention is directed to a composite heat sensor having both differential detection functions for detecting that the temperature rise rate is obtained. In the present invention for such a heat detector, a temperature sensitive element 2 whose resistance value Rt changes with a change in temperature, a first resistor R1, and a parallel circuit of a second resistor R2 and a capacitor C1 are connected in series. The temperature detection circuit 1 is connected to form the temperature detection circuit 1, and the first resistance R1 indicates that the resistance value Rt of the temperature sensing element 2 of the temperature detection circuit 1 becomes a value corresponding to a predetermined detection temperature or a predetermined temperature rise rate. Potential difference Vbe
The determination means 3 is provided to generate a constant temperature type and a differential type fire detection output by making a determination based only on the above.

[Operation] According to the heat sensor of the present invention having such a configuration,
When the ambient temperature rises sharply, the resistance value Rt of the thermistor as the temperature sensing element 2 is increased with the rapid rise in temperature.
Decreases and the potential at point a of the first resistor R1 on the temperature sensitive element 2 side rises sharply, but at point b on the second resistor R2 side is a capacitor.
It rises with a delay due to the charging of C1, and the potential difference across the first resistor R1 increases. Therefore, the first resistance
By controlling the base-emitter voltage of the transistor as the determination means 3 by the potential difference generated in R1, the transistor is turned on when a predetermined temperature rise rate is obtained, and differential fire detection can be performed.

On the other hand, when the ambient temperature gradually rises, the first resistance is applied to the change in the resistance value Rt of the temperature sensitive element 2 due to the temperature rise.
Since the rate of change of each potential at both ends of R1 is different and the potential difference generated in the first resistor R1 increases as the temperature rises, by applying this potential difference between the base and emitter of the transistor as the judging means 3, The constant temperature type fire detection can be performed by turning on the transistor when a predetermined temperature is reached.

[Embodiment] FIG. 1 is a block diagram of an embodiment showing one embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a temperature detection circuit, which is a thermistor 2 as a temperature sensitive element whose resistance value changes with temperature change, a delay circuit in which a first resistor R1 and a second resistor R2 and a capacitor C1 are connected in parallel. 4 are connected in series. The thermistor 2 as a temperature sensing element has a resistance value Rt, and the resistance value Rt of the thermistor 2 has a negative temperature coefficient that decreases substantially linearly with a temperature rise.

A judgment circuit 3 is provided for the temperature detection circuit 1. In this embodiment, the judgment circuit 3 includes a transistor 5 and a resistor R3.
Composed of. That is, the base of the NPN transistor 5 is connected to the connection point a between the thermistor 2 of the temperature detection circuit 1 and the first resistor R1.
And the emitter of the transistor 5 is connected to the connection point b between the first resistor R1 and the second resistor R2 of the temperature detecting circuit 1, so that the transistor 5 is connected to the first resistor R1 of the temperature detecting circuit 1.
It receives a bias due to the potential difference Vbe generated in the resistor R1 of.

The emitter of the transistor 5, which is the output of the judgment circuit 3, is
It is connected to the gate of SCR6 via a gate circuit consisting of resistor R6 and capacitor C3, and when transistor 5 is turned on, it triggers SCR6 and is connected between terminals L and C and has a low impedance between the power supply and signal line from the receiver. It is short-circuited to and the alarm current is made to flow.

Further, a diode bridge 7 is provided following the terminals L and C, and the terminals L and C for the power supply / signal line from the receiver are provided.
The connection polarity of is made non-polar. Diode bridge 7
After that, a constant pressure circuit 8 is provided, and a constant voltage by the constant voltage circuit 8 is supplied to the circuit section after the judgment circuit 3.

Further, a power-on reset circuit 9 is provided following the temperature detection circuit 1. The power-on reset circuit 9 has a transistor 10, resistors R4, R5, and a capacitor C2 are connected in series as a base circuit of the transistor 10. The base of the transistor 10 is connected between the resistors R4 and R5, and the resistor R4 A diode D1 is connected in parallel with.

This power-on reset circuit 9 is a judgment circuit 3 based on the detection output of the temperature detection circuit 1 when the sensor is powered on.
It is provided to prevent the malfunction of. That is, immediately after the power is turned on, the charging of the capacitor C2 is started via the resistors R4 and R5, so that the transistor 10 is turned on while the charging current is flowing through the capacitor C2. When the transistor 10 is turned on, the capacitor C1 is rapidly charged through the resistor R7, the potential at the point b is increased, the potential difference generated in the resistor R1 is controlled so as not to reach the bias voltage of the transistor 5, and the judgment circuit 3 is forced. The cut-off state is maintained, and the transistor 5 turns on in the unstable state immediately after the power is turned on and SC
Prevents malfunction of R6 being triggered.

 Next, the operation of the embodiment shown in FIG. 1 will be described.

First, the voltages Va and Vb at the points a and b of the first resistor R1 in the temperature detection circuit 1 are as follows.

Va = Vcc- (R1 + Ry) / (Rt + R1 + Ry) (1) Vb = Vcc-Ry / (Rt + R1 + Ry) (2) where Ry = R2 R3 / (R2 + R3) From the first (1) and (2) equations As is apparent, when the resistance value Rt of the thermistor 2 decreases due to the rise in ambient temperature, the voltages Va and Vb across the first resistor R1 increase. However, the rate of increase is larger at point a given by equation (1) and smaller at point b given by equation (2).

On the other hand, the resistance value of the thermistor 2 increases due to the sudden rise in ambient temperature.
When Rt sharply decreases, the voltages Va and Vb at points a and b on both ends of the first resistor R1 also increase as the resistance value Rt decreases.
For the voltage Vb at the lower b point, the voltage at the a point is set because the delay circuit 4 in which the resistor R2 and the capacitor C1 are connected in parallel is provided.
The voltage Vb at point b is delayed with respect to Va.

Figure 2 shows the first resistance when the ambient temperature increases rapidly.
The changes in the voltages Va and Vb across R1 are shown.

That is, in FIG. 2, the temperature gradually increased until time t1, but when the temperature started to increase rapidly from time t1, one voltage Va rapidly increased, while the other voltage Vb was delayed. Due to the delay caused by the circuit 4, the rate of increase is suppressed. Therefore, the potential difference between points a and b, that is, Vbe = Va-Vb, increases with a rapid temperature rise, and Vbe = 0.6V at time t2.
When it reaches, the transistor 5 of the judgment circuit 3 is turned on to generate a differential fire detection output, trigger the SCR 6, and send a warning current to the fire receiver.

FIG. 3 shows changes in the voltages Va and Vb across the resistor R1 when the ambient temperature rises slowly. As is clear from the equations (1) and (2), the voltage Va Since the rate of change is larger with respect to the voltage Vb and the temperature rise is slower at this time, the delay on the voltage Vb side due to the delay circuit 4 can be almost ignored, and the voltages Va and Vb are expressed by the equations (1) and (2) above. It rises at a rate determined by the resistance voltage division ratio of. Then, at time t1, when the potential difference generated in the resistor R1, that is, Vbe = Va−Vb reaches 0.6V, the transistor 5 is turned on, the fire detection output by the constant temperature type is generated, the SCR6 is triggered, and the alarm current is sent to the receiver. It will be sent out.

Although the thermistor is taken as an example of the temperature sensitive element in the above-described embodiment, an appropriate element such as a varistor whose resistance value changes with temperature change can be used.

[Effects of the Invention] As described above, according to the present invention, the temperature detection circuit and the determination circuit provided with a single temperature sensitive element generate a fire detection output when a predetermined temperature is reached, and a temperature rise. It is possible to realize both differential fire detection functions that generate a fire detection output when the rate reaches a predetermined value, and it is possible to minimize the number of parts and achieve a significant cost reduction.

[Brief description of drawings]

 FIG. 1 is a block diagram of an embodiment showing an embodiment of the present invention; FIG. 2 is an explanatory diagram of a differential detection operation of the present invention; and FIG. 3 is an explanatory diagram of a constant temperature fire detection operation of the present invention. is there. 1: Temperature detection circuit 2: Thermistor (temperature sensitive element) 3: Judgment circuit (means) 4: Delay circuit 5,10: Transistor 6: SCR 7: Diode bridge 8: Constant voltage circuit 9: Power-on reset circuit R1: First 1st resistance R2: 2nd resistance C1: Capacitor

Claims (1)

(57) [Scope of utility model registration request] 1. A constant temperature method for detecting the arrival of a predetermined temperature when the resistance value of the temperature sensitive element reaches a predetermined value, and a rate of change of the resistance value of the temperature sensitive element reaches a predetermined value. In a composite type heat sensor having both a differential type detection function for detecting that a predetermined temperature rise rate is obtained, the resistance value changes as the temperature changes and the temperature sensing element, the first resistance, and the A temperature detection circuit is configured by connecting a parallel circuit of two resistors and a capacitor in series, and the resistance value of the temperature sensing element of the temperature detection circuit has reached a predetermined detection temperature or a value corresponding to a predetermined temperature rise rate. A heat detector characterized by comprising a judging means for generating the constant temperature type and the differential type fire detection outputs by discriminating only from a potential difference generated in the first resistance.