JPS635495A - Differential type heat sensor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] 〔Technical field〕 The present invention relates to improvements in differential heat sensors.

[Background technology]

A conventional heat sensor of this type is configured to detect a temperature rise based on the temperature difference between two thermistors having different thermal time constants.

FIG. 7 shows an example of a differential heat sensor. A is a switching circuit operated by the output signal of the comparator CP, and B is a power supply circuit. TH1' is a thermistor with a fast thermal time constant and is installed in a place that is directly in contact with the outside air, and TH2' is a thermistor with a slow thermal time constant that is installed in a place that is not in direct contact with the outside air, e.g.
Provided inside the sensor. Thermistor THI', TH
Resistors R1 and R2 constitute a voltage dividing circuit together with each of 2'.
The voltage Va' at point a' is the voltage Va' at point b' at room temperature.
The value is selected to be slightly lower than b'.

To explain the operation of such a heat sensor, when a sudden temperature rise occurs, the resistance value of thermistor THI' decreases, so when Va'>Vb', the output of comparator CP becomes high level rHJ, and switching Operate circuit A. In addition, when the temperature rises slowly, T
Since the resistance value of l(2' decreases, Va'<Vb', the output of the comparator CP maintains the low level rLJ, and the switching circuit A is not operated.

By the way, if we consider the actual conditions of use of such a heat sensor and consider it further, we will find that the power supply voltage is IOV, R
1 is IMΩ, and the thermistor TH1' is IOMΩ at -10°C.

0℃〃〃　　5MΩ.

20℃〃〃　　1MΩ.

30″c #500Ω.

50'C# 200Ω.

60℃　　　　　　100KΩ.

Let's consider the case of using a resistor with a resistance value of .

First, when the temperature rises rapidly from 20℃ to 30℃,
The voltage increase ΔVa' at this time is 1M + IM 500 + 1M -6,7V, so °, ΔVa,'=Va' (30℃) - Va' (20℃
)=1.7V, which increases by about 1.7V.

Also, the voltage increase ΔV when changing from -10℃ to 0℃
a' is 10M+IM 5M+IM, °, ΔVa'-++Va' (0℃) -Va' (
-10℃) = O, SV, which increases by about 0.8 ■.

Furthermore, if the temperature changes from 50℃ to 60℃, the temperature increases to 200+
+1M to 1M 100, .DELTA.Va' = Va' (60℃) - Va'(
50°C) -0.8V, which increases by about 0.8V.

On the other hand, the voltage of ■b' is 6.7V at 20°C.
To make it, 1M+R2,', R2=2.0MΩ Therefore, choose the value of resistor R2 to be 2.0MΩ, then -10
Voltage V b ' at point b in case of °C (-10 °C)
is 10M + 2M Similarly, in the case of 50℃, if the voltage vb' at point b' is set 1.7v higher than the voltage Va' at point a' at 20℃, as above +2M to 200, the voltage at 10℃ Due to the temperature rise, Va'>Vb' and the sensor will operate. However, even with the same temperature increase of 10°C, from 20°C to 30°C, Va' increases by 1.7V, whereas from -10°C to 0°C, it increases by 0.8V, 50°C.
Since the temperature rises by only 0.8 VL from .degree. C. to 60.degree. C., considering the variation in the thermistor constant, it can be seen that the operating sensitivity is affected by the temperature of the atmosphere. Therefore, even if the device is set to operate normally when the temperature rises from room temperature, the sensitivity changes significantly when the temperature rises from a low temperature or from a high temperature, resulting in low reliability.

[Purpose of the invention]

The present invention was developed in view of the above circumstances, and has the purpose of providing a highly reliable differential heat sensor that operates accurately against sudden temperature rises in any temperature atmosphere. There is.

[Disclosure of the invention]

The present invention is proposed to achieve the above objects,
Using a common power supply voltage, an impedance voltage divider circuit and a CR
circuits are connected in parallel, and a diode is interposed between the intermediate connection points of these two circuits so that its cathode is connected to the intermediate connection point of the voltage divider circuit, and the voltage difference between the two intermediate connection points is The differential heat sensor is configured to detect and operate, and the voltage divider circuit connects two thermistors in series that have the same resistance value, the same thermistor constant, and different thermal response characteristics. It is characterized by being configured by being connected to.

FIG. 1 shows a configuration diagram of a differential heat sensing section (2) which constitutes the essential part of the present invention.

As shown in the figure, the heat sensing section I has an impedance voltage divider circuit l and a CR circuit 2 connected in parallel with each other using a common power supply voltage. A diode D is interposed between the connection point a and the connection point A of the CR circuit 2 so that its cathode is connected to the connection point a of the voltage divider circuit 1, and when there is a sudden change, the voltage Va and A voltage difference is generated between voltage vb and the sensor is activated.

Here, the impedance voltage divider circuit 1 includes two thermistors Zl and Z2 that have the same resistance value and thermistor constant (hereinafter referred to as B constant) and have different thermal response characteristics (in the configuration example, Zl has a thermal time constant A fast one and a slow one with a slow thermal constant are selected for Z2) connected in series.

In the heat sensor of the present invention having such a heat sensing part (2), two thermistors Zl and Z
Since the resistance values of 2 are equal, the voltage Va at point a is a constant value (1/2 of the power supply voltage ■0), but when capacitor C of CR circuit 2 is charged via resistor R, the capacitor C That is, since the voltage vb at point b is higher than the forward voltage drop Vd of the diode D, the condition of Va<Vb is satisfied and the sensor is not activated.

However, when a sudden change in temperature occurs, the resistance value of thermistor Z1 decreases and thermistor Z2 does not change because its thermal response is slow), and Va rapidly increases, so diode D becomes reverse biased and becomes non-conductive. Therefore, capacitor C is charged via resistor R. However, since the capacitor C of the CR circuit 2 has a resistor R, the charging speed is slow.
Since the voltage rise of vb is delayed and becomes Va>Vb, the sensor is activated at this time.

To explain the operation of the present invention more specifically, for example, 20
When the temperature suddenly rises from a temperature atmosphere of ℃ to 10℃, the resistance value of Zl changes from LMΩ to 500Ω, but the resistance value of Z2 remains the same, so 1, °, AV = Va - Vb = 1
．． 7V, and when the temperature rises rapidly from -10℃ to 0℃, 1, . ΔV=Va-Vb-1,7V Furthermore, when the temperature atmosphere changes from 50°C to 60°C, ZυOK+200K, ·, ΔV=Va-Vb-1. 7V, the voltage difference between Va and Vb is constant no matter the temperature, and a temperature rise can be detected.

EXAMPLES Specific examples of the present invention will be described below with reference to the accompanying drawings.

Figure 2 shows a thermistor THI with negative resistance-temperature characteristics.
, TH2 shows an example in which the impedance voltage divider circuit 1 is configured with the same resistance value and B constant, THI has a fast thermal time constant, and TH2 has a slow thermal time constant. There is. A comparator CP compares the voltage Va at the intermediate connection point a of the impedance voltage divider circuit l with the voltage vb at the intermediate connection point S of the CR circuit.

In an atmosphere with no temperature change, the voltage Va at point a is Vo/
2 (here, Vo is the power supply voltage), and the voltage at point b is vb
is higher than the voltage at point a by the voltage drop Vd of diode D, so the input condition for comparator CP is V
Since a<Vb, the output is low level, and the switching circuit A is not activated.

However, when a sudden temperature rise occurs, the resistance value of THI decreases and Va rises rapidly, but the rise of vb is delayed due to the large self-constant of the CR circuit, and the input condition of comparator CP is Va> Vb and a high level output, so switching circuit A is activated at this time. In addition, B
is the power supply circuit.

FIG. 3 shows a second embodiment, in which V
a and Vb are compared.

Thermistor THI constituting impedance voltage divider circuit 1
TH2 is the same as that shown in Figure 2, and the switching circuit A is configured to operate by making the transistor Tl conductive by the output of PUT and sending a gate trigger signal to the SCR. The power supply circuit B uses a full-wave rectifier circuit BD. The part surrounded by C is a charging circuit that charges the capacitor C of the CR circuit 2 when the power is turned on.
It is composed of a PNP type transistor T2. Note that CI is a capacitor and R1-R4 are resistors.

FIG. 4 shows an example of another arrangement of the present invention in which a constant temperature sensing section (2) is provided after the differential heat sensing section (1) shown in FIG. 3 to constitute a thermal composite sensor. ing.

The parts that overlap with those in FIG. 3 are given the same reference numerals and their explanations are omitted.
The gate of I is the impedance voltage divider circuit 1 of the heat sensing part I.
, the anode is connected to the intermediate connection point C of a voltage dividing circuit consisting of a resistor R5 and another thermistor TH3, and the cathode is commonly connected to the cathode of PUT of the heat sensing section I. Transistor T of switching circuit A
It is connected to the base of 1.

THI to TH3 have the same resistance value and B constant, but THI has a fast thermal time constant, and TH2 and TH3 have a slow thermal time constant.

Now, to simplify the explanation, THI at 20℃~
The resistance value of TH3 is 900Ω, and it is 1 at 70℃.
Considering the case where 00 is Ω and R5 is 100KΩ, the voltage Va at point a is: 900Ω+900Ω The voltage Vc at point 0 is: 100Ω+900Ω.

Here, when the temperature suddenly rises to 70°C, only THI, which has a fast thermal time constant, responds, so Vc does not change.
The voltage Va at point a becomes 100Ω+900Ω, and PUTI is turned on.

FIG. 5 shows an operation time chart in this case.

On the other hand, when the temperature rises slowly, TH2,
The resistance value of TH3 also decreases, but since the resistance value of THI does not change, Va does not change, Vc decreases, becomes 100Ω, 100Ω+100KΩ, and PUTI is turned on.

FIG. 6 shows an operation time chart in this case.

Thus, in this example, three thermistors THI
By using .about.3, the temperature increase rate and constant temperature point can be detected with high accuracy.

〔Effect of the invention〕

As can be understood from the above explanation, according to the differential heat sensor of the present invention, the voltage difference can be kept constant when the temperature rises, regardless of the temperature of the atmosphere, so the temperature rise can be accurately detected. A highly reliable differential heat sensor can be obtained.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the principle of the heat sensing section of the differential heat sensor of the present invention, FIGS. 2 to 4 are illustrations of specific embodiments of the differential heat sensor, and FIGS. FIG. 6 is a time chart explaining the operation of the heat sensor shown in FIG. 4, and FIG. 7 is a layout of a conventional differential heat sensor. (Explanation of symbols) 1... Impedance voltage divider circuit 2... CR circuit ■... Differential heat sensing section ■... Constant temperature heat sensing section

Claims (1)

[Claims] Using a common power supply voltage, an impedance voltage divider circuit and a CR
circuits are connected in parallel, and a diode is interposed between the intermediate connection points of these two circuits so that its cathode is connected to the intermediate connection point of the voltage divider circuit, and the voltage difference between the two intermediate connection points is The differential heat sensor is configured to detect and operate, and the voltage divider circuit connects two thermistors in series that have the same resistance value, the same thermistor constant, and different thermal response characteristics. A differential heat sensor characterized in that it is configured by being connected to.