JP2685854B2 - Differential heat sensor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a differential heat sensor using a thermistor as a heat sensitive element.

[Prior Art] A differential heat sensor generates a detection output when the ambient temperature rises at a constant temperature rise rate or more. As this type of differential thermal sensor, there is a thermal sensor using a thermistor.

[Problems to be Solved by the Invention] However, a differential thermal sensor using this type of thermistor cannot ignore the change in sensitivity due to the ambient temperature. In other words, the resistance change rate of the thermistor decreases as the normal temperature rises, so the sensitivity is poor when the ambient temperature rises from a high temperature, and the sensitivity is sensitive when the ambient temperature rises from a low temperature. It becomes.

The present invention has been made in view of the above points, and an object of the present invention is to provide a differential thermal sensor having a small sensitivity change even if the ambient temperature rises from any temperature. It is in.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a reference output generating means in accordance with the ambient temperature in a direction in which the detection sensitivity of the comparison circuit is made constant regardless of the ambient temperature at the time when the temperature rise starts. Is equipped with a temperature compensation circuit for varying the output of the.

[Operation] According to the present invention, by providing the above-mentioned temperature compensating circuit and varying the output of the reference output generating means in accordance with the ambient temperature,
The detection sensitivity of the comparison circuit is made constant irrespective of the ambient temperature at the start of the temperature rise, so that the sensitivity change is reduced even if the ambient temperature rises from any temperature.

[Embodiment] FIG. 1 shows a circuit configuration of an embodiment of the present invention, and FIG. 2 is a block diagram showing a schematic configuration thereof. This differential heat sensor (hereinafter referred to simply as "sensor") is connected to a fire receiver by a sensor line 1 consisting of a pair of signal lines, and this sensor causes the ambient temperature to rise to a constant temperature. When it is detected that the rate is higher than the rate, the detection output is sent to the fire receiver by short-circuiting the signal lines of the sensor line 1 to which the voltage is applied.

In the sensor of this embodiment, a diode bridge DB is provided at the input so that the sensor can be connected to the sensor line 1 with no polarity. The capacitor C ₈ and Zener diode ZD ₁ connected to the output of this diode bridge DB are for absorbing surge.

The power supply circuit 2 makes the output voltage of the diode bridge DB a constant voltage and supplies power to the latter stage circuit. The power supply circuit 2 includes a constant voltage section composed of a transistor Q ₃ , a zener diode ZD ₂ and a resistor R ₅ , and a transistor Q ₄ And a resistor R ₈ and an inrush current limiter. The inrush current limiting unit, when a predetermined value or more current flows into the resistor R _8, transistor Q ₃
In order to prevent the above-mentioned current from flowing by lowering the base potential of, the inrush current at power-on is limited.

From the power supply circuit 2 to the temperature detection circuit 3 and the comparison circuit 4
Is supplied with power. As shown in FIG. 5, the temperature detection circuit 3 includes a thermistor TH ₁ that responds quickly to the ambient temperature by exposing the heat-sensitive part to the outside of the housing 6 of the sensor, and a gentle response to the ambient temperature that is housed in the housing 6. A thermistor
With TH ₂ . These thermistors TH ₁ and TH ₂ are connected in series to the output of the power supply circuit 2, and the thermistor TH ₁ and TH ₂ differ in response speed with respect to the ambient temperature.
_The sense output V _S appears as a voltage signal at the connection point between ₁ and TH ₂ .
That is, when the ambient temperature is constant, the thermistors TH ₁ , TH ₂
When the ambient temperature rapidly rises due to the voltage determined by the voltage division ratio of the resistance component of the thermistor output V _s , the resistance value of the thermistor TH ₁ rapidly decreases and the thermistor T 1
Since the resistance value of H ₂ gradually decreases without following the increase of the ambient temperature, the difference in resistance value is generated between the thermistors TH ₁ and TH _2, and the sensing output V _s decreases. If the temperature rise stops halfway, the sensing output V _s
Is stable at a constant value. Also, when the rate of temperature rise is extremely gentle, the change in resistance value of the thermistor TH ₂ follows the change in ambient temperature, so the resistance values of the thermistors TH ₁ and TH ₂ decrease at approximately the same rate. The sensing output V _s is kept almost constant.

The sensing output V _s is input to the comparison circuit 4 described later and also to the reference output generation unit that creates the reference output of the comparison circuit 4. This reference output generator is composed of buffers B ₁ ,
B ₂ , transistor Q ₅ , diodes D _{1 to} D ₃ , capacitor C ₃
〜C ₅ and resistors R ₁₀ 〜 R _13, it keeps the voltage according to the sensing output V _s when the ambient temperature is not rising, and keeps it constant from the holding voltage at the start of rising when the ambient temperature rises. The output is reduced at the rate of change. Here, when the power is turned on, at this time, the sensing output V _s determined by the voltage division ratio of the thermistors TH ₁ and TH ₂ is output. Therefore, the transistor Q ₅ and the diodes D ₁ and D ₃ are turned on and the capacitor C
₃ is charged to a predetermined voltage according to the sensing output V _s . The voltage V _C charged to this capacitor C ₃ is V _C = V _S −V _BE −V _F1 −V _F3 where V _{BE is} the base-emitter voltage of transistor Q ₅ , and V _{F1 is} the forward direction of diode D ₁ . Voltage, V _F3 : Diode D ₃
Forward voltage. If the temperature rises now, the sensing output V _s decreases as described above, so that the transistor Q ₅ and the diodes D ₁ and D ₃ are turned off, and the charge of the capacitor C ₃ is charged by the diode D ₂ and the resistor R ₁₂ , Is discharged via R ₁₃ . Therefore, the output of the reference output generator decreases at a constant rate of decrease. When the temperature rise stops or the temperature falls, the decrease of the sensing output V _s stops or rises, so the transistor Q ₅ and the diodes D ₁ and D ₃ are turned on and the sensing output V _s is changed according to the sensing output V _s . Voltage is charged in the capacitor C ₃ . The output of this reference output generator is divided by resistors R ₁₀ and R ₁₁ and output to reference circuit 4 as reference voltage V _r . here,
The output of the buffer B ₂ is provided with the diodes D ₄ and D ₅ which compose the temperature compensating circuit 1 according to the present invention. The operation of the temperature compensating circuit 1 will be described later. As is apparent from the above description, this reference output generation unit determines the rate of increase in the ambient temperature for determining a fire. Incidentally, it is possible to adjust the sensitivity of the sensor by changing the resistance value of the resistor R ₁₀ to R ₁₃ of the reference output generating unit. Also the buffer
B ₁ and B ₂ are capacitors C ₄ and C ₅ for impedance conversion.
Is provided for noise absorption.

The comparator circuit 4 compares the sensing output V _s with the reference output V _r to detect that the rate of increase in ambient temperature is above a certain level. Now, when the ambient temperature is constant, the sensing output V _s is higher than the reference output V _r , so the output of the comparison circuit is at a low level. However, the ambient temperature rises rapidly due to fire, etc.
When it becomes larger than the reference rate of rise determined by the discharge time constant of C ₃ , the sensing output V _s falls below the reference output V _r , and the comparison circuit 4
Output becomes high level.

The output of the comparison circuit 4 drives the switching circuit 5. This switching circuit 5 is a diode bridge DB
SCRQ _0, which is connected to the output of the sensor and shorts the sensor line 1, and the transistors Q ₁ and Q ₂ that trigger this SCRQ ₀ and the capacitors
It is composed of a trigger circuit composed of C ₁ , C ₂ , C ₇ and resistors R _{1 to} R ₇ , and when the output of the comparison circuit 4 becomes high level, the transistors Q ₁ , Q ₂ are turned on and SCRQ ₀ Trigger. When SCRQ ₀ is turned on in this manner, the signal lines of the sensing circuit 1 are short-circuited and the sensing output is sent to the fire receiver.

FIG. 5 shows the structure of the sensor head, which is mounted on a base mounted on the construction surface. The housing 6 of this head is composed of a body 7 and a cover 8, and a thermistor TH ₂ and electronic parts constituting the above circuit are mounted on a printed circuit board 9 housed in the body 7. The thermistor TH _{1 is} also mounted on the printed circuit board 9, but the thermistor TH ₁ is formed in the shape of a match rod to have a high height, and the insertion hole 10 drilled in the central portion of the cover 8 is used. Is mounted upright on the printed circuit board 9 so that the heat sensitive portion at the tip is exposed. The terminals 11 protruding from the upper surface of the body 7 are for mechanically and electrically connecting to the base.

The basic operation of this sensor will be briefly described. When the ambient temperature is constant, the resistance values of the thermistors TH ₁ and TH ₂ are also constant, and the sensing output V _s determined by the voltage division ratio of these thermistors TH ₁ and TH ₂ is supplied to the comparison circuit 4 and the reference output generator. Is entered. In this case, the sensing output V _s does not drop below the reference output V _r , so the output of the comparison circuit 4 is at a low level and SCRQ _{0 of the} switching circuit 5 is off.

Now, when a fire occurs and the ambient temperature rapidly rises, a difference occurs in the resistance value between the thermistors TH ₁ and TH _2, and the sensing output V _s rapidly decreases. At this time, the reference output V _r also decreases at a constant rate as the capacitor C ₃ discharges. However, at this time, since the temperature rise rate is high, the sensing output V _s decreases faster than the reference output V _r decreases.
As a result, the sensing output V _S becomes lower than the reference output V _r as shown in FIG. 3 (b). In this case, the comparison circuit 4
Output becomes high level and SCRQ of switching circuit 5
_{When 0} is turned on, a detection output indicating that there is a fire is sent to the fire receiver through the detector circuit 1. The fire receiver that receives this detection signal performs a notification operation such as issuing an alarm.

It should be noted that although the sensing output V _S also decreases when the ambient temperature rises relatively slowly, the sensing output V _{s at} this time is the third
As shown in FIG. 6A, the output does not drop below the reference output V _r , so the output of the comparison circuit 4 remains at the low level, and no detection output is generated. In other words, a comparatively gradual change in ambient temperature due to an increase in temperature or the use of heating equipment is not judged as a fire.

By the way, in the sensor using the thermistors TH ₁ and TH ₂ of this type, the change of the sensing output V _s varies as shown in FIG. 4 depending on the ambient temperature rise.
Fig. 4 shows the case where the temperature rises from -10 ℃ and 50 ℃, and the case where the temperature rises from the state where the ambient temperature is high as shown in (a) of Fig. As shown, the change in the sensing output V _s is smaller than that when the ambient temperature is low and the temperature rises. Therefore, the temperature compensating circuit 1 is provided at the output of the buffer B ₂ , and the reference output V _r is changed by the temperature change amount of the forward voltage of the diodes D ₄ and D ₅ forming the temperature compensating circuit 1, and The detection sensitivity is made constant. That is, at low temperature, the diodes D ₄ , D
_Since the forward voltage of ₅ increases and the reference output V _r decreases as shown in D of FIG. 4, the detection sensitivity of the comparison circuit 4 decreases, and when the temperature compensation circuit 1 is not provided, it becomes sensitive at low temperature. Offset the amount. Conversely, when the temperature is high, the diode
Since the forward voltage of D ₄ and D ₅ is lowered and the reference output V _r is increased as shown in FIG. 4C, the sensitivity of the comparison circuit 4 is increased and the sensitivity which becomes insensitive at high temperature is offset. Therefore, no matter what temperature the ambient temperature rises, there is less change in the sensor's sense.

In this type of differential heat sensor, there is a distinction between one type and two types, and one type operates with a smaller temperature rise rate. The circuit of FIG. 1 shows two types of sensors, and in the case of one type, it is the circuit of FIG. That is, in the case of one type, the voltage difference between the sensing output V _s and the reference output V _r is set small as shown in FIG. Therefore, since the sensitivity change with respect to the ambient temperature is small, the fluctuation of the reference output V _r with respect to the ambient temperature may be small as shown in C and D of FIG. Therefore, temperature compensation is performed using only the diode D ₄ . The first
It is also possible to combine the circuits of FIG. 6 and FIG. 6 into a sensor having two types of sensitivity.

EFFECTS OF THE INVENTION As described above, according to the present invention, the temperature at which the reference output of the reference output generation means is varied in accordance with the ambient temperature in a direction in which the detection sensitivity of the comparison circuit becomes constant irrespective of the ambient temperature at the start of temperature rise. Since the compensating circuit is provided, the detection sensitivity of the comparison circuit can be made constant regardless of the ambient temperature at the time when the temperature rise starts, so that the sensitivity change of the sensor can be obtained even if the ambient temperature rises from any temperature. Has the advantage of being less.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of an embodiment of the present invention, FIG. 2 is a block diagram showing a schematic circuit configuration of the same, and FIGS. 3 (a) and 3 (b) are respectively the same operation. Explanatory drawing, FIG. 4 is explanatory drawing which shows the temperature compensation characteristic same as the above, FIG. 5 (a)-(c) is the front view, bottom view, and part which fractured | ruptured a part of head of the differential type thermal sensor same as the above. FIG. 6 is a plan view, FIG. 6 is a circuit diagram of another embodiment, and FIG. 7 is an explanatory diagram showing temperature compensation characteristics of the same. 1 is a temperature compensation circuit, 2 is a power supply circuit, 3 is a temperature detection circuit,
Reference numeral 4 is a comparison circuit, 5 is a switching circuit, TH ₁ and TH ₂ are thermistors, and 1 is a sensor line.

Claims (1)

(57) [Claims] 1. A first thermistor which responds quickly to ambient temperature, a 42nd thermistor whose response speed to ambient temperature is slower than that of the first thermistor, and a sensor line formed by a pair of signal lines. The voltage at the connection point between the power supply circuit in which the voltage is made constant and the output is connected to the first and second thermistors in series, and the connection point between the first and second thermistors when the ambient temperature is not rising. Reference output generating means for holding a voltage according to a certain sensing output and varying the output at a constant rate of change from the holding voltage at the start of rising when the ambient temperature rises, and the output of the reference output generating means and the sensing output. And a switching circuit that short-circuits the signal lines of the sensor line that is driven by the output of this comparison circuit, Differential heat detector comprising a temperature compensation circuit for varying the output of the reference output generating means according to the ambient temperature detection sensitivity of the circuit in the direction of a certain reduction irrespective of the ambient temperature of the temperature increase start time.