JP3519464B2 - Heat detector - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat detector which outputs a differential output and a constant temperature output.

[0002]

2. Description of the Related Art Conventionally, as a heat sensor of this type, for example, one shown in FIG. 4 has been known. This thermal sensor uses a thermistor element with a slow thermal response and a thermistor element with a fast thermal response whose resistance value changes according to the temperature change. It has both a constant temperature function to issue a warning when the temperature reaches a certain level and a differential function to detect and issue a warning when the temperature in the monitored area suddenly rises above a predetermined rate of temperature rise.

In FIG. 4, 1 is a positive connection terminal, 2
Is a negative connection terminal, and these connection terminals 1 and 2 are
Is connected to a transmission line extended from a receiver (not shown) installed in the central monitoring room, etc., so that power is supplied from the receiver via the transmission line and a fire alarm is returned. There is. A power supply voltage made constant by a constant voltage circuit (not shown) is supplied between the connection terminals 1 and 2.

Reference numerals 3 and 4 are thermistor elements having a negative temperature characteristic in which the resistance value decreases as the temperature rises.
One of the thermistor elements 3 has a large thermal time constant, so that the thermal response is slow, and the other thermistor element 4 has a small thermal time constant, so that the thermal response is fast. Thermistor element 3 with slow thermal response
And the thermistor element 4 having a high thermal response and the resistor 5 are connected in series to form a series circuit 6.

The resistors 7, 8 and 9 are connected in series to form a reference voltage generating circuit 10. Resistance 7
A first reference voltage (VC) is generated at the connection point (C) between the resistor 8 and the resistor 8, and a second reference voltage (VB) is generated at the connection point (B) between the resistor 8 and the resistor 9.

The first reference voltage (VC) generated by the reference voltage generation circuit 10 is input to the positive input terminal of the first comparator 11, and the thermistor element 3 having a slow thermal response and the thermistor having a fast thermal response are input. The voltage (VA1) at the connection point (A1) between the elements 4 is input to the negative input terminal of the first comparator 11. When the temperature rises rapidly, the voltage (VA1) at the connection point (A1) falls rapidly as shown in D of FIG. When the voltage (VA1) becomes lower than the first reference voltage (VC), the output of the first comparator 11 becomes "H" level, and the temperature in the monitored area suddenly rises beyond the predetermined temperature rise rate. When this is detected, an alarm is issued.

When the temperature rises slowly, E in FIG.
As shown in, the voltage (VA1) at the connection point (A1) gradually decreases. Reference numeral 12 is a second comparator, and the negative input terminal of the second comparator 12 has a reference voltage generating circuit 10
The second reference voltage (VB) generated in step 2 is input, and the thermistor element 4 and the resistor 5 with fast thermal response are input to the positive input terminal.
The voltage (VA) at the connection point (A) is input.

When the temperature rises rapidly, the voltage (VA) at the connection point (A) rises rapidly as shown in F of FIG. When the temperature rises slowly, the voltage (VA) at the connection point (A) rises slowly as shown in G of FIG. FIG. 5 is a diagram showing a differential output and a constant temperature output when the temperature rise rate is high. In FIG. 5, as described above, D
Is the connection point of the thermistor element 3 and the thermistor element 4 (A
1) shows the voltage (VA1), and when the temperature rises rapidly, the voltage (VA1) falls rapidly. Voltage (VA
When 1) becomes lower than the first reference voltage (VC) at the connection point (C) of the resistors 7 and 8, the output of the first comparator 11 becomes "H" level and a differential output is obtained. In this case, a case where the temperature in the monitored area suddenly rises beyond a predetermined rate of temperature rise is detected, and an alarm is issued by differential output.

The above-mentioned F indicates the voltage (VA) at the connection point (A) between the thermistor element 4 and the resistor 5, and the voltage (VA) indicates that the temperature rises rapidly due to the rapid rise in temperature. Indicates that the timing of exceeding the second reference voltage (VB) is later than the differential output. FIG. 6 is a diagram showing a differential output and a constant temperature output when the temperature rise rate is low.

In FIG. 6, the above-mentioned G is a connection point (A).
The voltage (VA) is shown, and the voltage (VA) rises slowly when the temperature rises slowly. The voltage (VA) is the second
When the voltage exceeds the reference voltage (VB), the output of the second comparator 12 becomes "H" level and a constant temperature output is obtained. It is detected that the temperature in the monitoring area has reached a preset dangerous temperature, for example, 60 degrees, and the alarm is issued by the constant temperature output.

The above E is the voltage (VA) at the connection point (A1).
1), the voltage (VA1) decreases slowly because the temperature rises slowly. FIG. 6 shows that the timing at which the voltage (VA1) becomes lower than the first reference voltage (VC) and differential output is performed is later than the constant temperature output.

[0012]

However, in such a conventional heat detector, as shown in FIG. 7, the voltage (VA) at the connection point (A) is varied due to the variation of the individual two thermistor elements. ) Changes as indicated by the dotted line, the constant temperature point intersecting the second reference voltage (VB) is displaced,
An error of the constant temperature point as shown by the arrow H occurs.

Further, due to the difference in temperature rise rate (VA
Since the voltage (VA) changes as shown in (A), an error occurs with respect to the constant temperature point as shown by the arrow (I). The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a heat sensor capable of reducing an error in constant temperature operation and improving accuracy of constant temperature output. .

[0014]

In order to achieve the above object, according to the present invention, a first temperature detecting element having a slow thermal response, a second temperature detecting element having a fast thermal response, and a resistor are connected in series. And the first series voltage generated by the first reference voltage generating means.
And a first comparator to which the voltage at the connection point between the first temperature detection element and the second temperature detection element is input,
A second reference voltage that is proportional to the voltage at the connection point between the first temperature detection element and the second temperature detection element, and a second reference voltage that is input at the voltage at the connection point between the second temperature detection element and the resistor Equipped with a comparator.

Further, according to the present invention, a buffer amplifier connected to a connection point of the first temperature detecting element and the second temperature detecting element, and a second pair of resistors connected in series to the buffer amplifier. By the reference voltage generating means of
Generates the reference voltage of. Further, when the resistance value of the pair of resistors used in the present invention is sufficiently large, the buffer amplifier is not necessary.

In the present invention, the second reference voltage is set to A
Input as the reference voltage Vref of the / D converter,
The voltage at the connection point between the second temperature detecting element and the resistor is input to the A / D converter.

[0017]

According to the heat sensor of the present invention having such a configuration, the second reference voltage proportional to the voltage at the connection point between the first temperature detecting element and the second temperature detecting element is generated, Second
Since the reference voltage and the voltage at the connection point of the second temperature detecting element and the resistor are compared to obtain a constant temperature output, the error due to the variation in the individual temperature detecting elements is reduced from two to one. Further, the error due to the difference in the temperature rise rate is eliminated, and the accuracy of constant temperature output can be improved.

Further, since the second reference voltage is input as the reference voltage of the A / D converter and the voltage at the connection point of the second temperature detecting element and the resistor is input to the A / D converter, the constant temperature is maintained. The accuracy of the output digital value can be improved.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 are views showing an embodiment of the present invention. FIG. 1 is a circuit diagram showing an embodiment of the present invention. Figure 1
, 21 is a plus connection terminal, 22 is a minus connection terminal, and these plus connection terminal 21 and minus connection terminal 22 are extended from a receiver (not shown) installed in a central monitoring room or the like. Connected to the established transmission line,
In addition, a constant voltage generated by a constant voltage circuit (not shown) is supplied to the connection terminals 21 and 22 as a power supply voltage.

Reference numeral 23 is a first thermistor element (first temperature detecting element) having a negative temperature characteristic in which the resistance value decreases as the temperature rises. Since the first thermistor element 23 has a large thermal time constant, it has a thermal response. It has the property of slow sex. Reference numeral 24 is a second thermistor element (second temperature detecting element) having a negative temperature characteristic in which the resistance value also decreases with temperature rise.
Since the second thermistor element 24 has a small thermal time constant, it has a characteristic of quick thermal response.

The first thermistor element 23, the second thermistor element 24 and the resistor 25 are connected in series, and the series circuit 2
6 is composed. Reference numeral 27 denotes a first reference voltage generating circuit as a first reference voltage generating means, which is composed of a resistor 28 and a resistor 29 connected in series. The first reference voltage generation circuit 27 generates a first reference voltage (VC) at the connection point (C) of the resistors 28 and 29.

Reference numeral 30 is a first comparator. The first reference voltage (VC) is input to the positive input terminal of the first comparator 30, and the first thermistor element 23 is input to the negative input terminal.
And the voltage (VA1) at the connection point (A1) of the second thermistor element 24 is input. Voltage at connection point (A1) (VA
In 1), when the temperature rise rate is high, as shown in D of FIG. 5, it rapidly decreases, and when the temperature rise rate is low, E of FIG.
As shown in, it gradually decreases.

When the temperature rise rate is high, the voltage (VA1)
Rapidly decreases and becomes lower than the first reference voltage (VC), the output of the first comparator 30 becomes "H" level, and a differential output is obtained. That is, it is detected that the temperature in the monitored area has risen sharply beyond the predetermined rate of temperature rise, and an alarm is issued. This is the differential function.

Reference numeral 31 denotes a second reference voltage generating circuit as a second reference voltage generating means, which is composed of a series circuit in which a buffer amplifier 32, a resistor 33 and a resistor 34 are connected in series. The input side of the buffer amplifier 32 has a connection point (A) between the first thermistor element 23 and the second thermistor element 24.
The resistor 33 and the resistor 34 are connected in series on the output side. The voltage at the connection point (A2) is input to the buffer amplifier 32, converted into a voltage of the same potential by the buffer amplifier 32, and then the voltage is applied to the resistors 33 and 3.
It is divided by 4. This divided voltage becomes the second reference voltage. That is, the voltage at the connection point (B1) between the resistors 33 and 34 becomes the second reference voltage (VB1). The second reference voltage generating circuit 31 includes the first thermistor element 2
The second reference voltage (VB1) proportional to the voltage at the connection point (A2) between the third thermistor element 24 and the third thermistor element 24 is generated.

Reference numeral 35 is a second comparator, and the negative input terminal of the second comparator 35 has a first thermistor element 23.
And a second reference voltage (VB1) proportional to the voltage at the connection point (A2) between the second thermistor element 24 and the second thermistor element 24 are input, and the connection point (A) between the second thermistor element 24 and the resistor 25 is input to the positive input terminal. Voltage (VA) is input. The second reference voltage (VB1) is shown by J in FIG. 2, and when the voltage at the connection point (A2) between the first thermistor element 23 and the second thermistor element 24 decreases, it is proportional to the voltage decrease. , K in Figure 2
As shown in.

In addition, the second thermistor element 24 and the resistor 2
The voltage (VA) at the connection point (A) of No. 5 rises as the temperature rises, as shown by L in FIG. 2, and due to the difference in temperature rise, the rate of rise decreases as shown by M. To do. next,
The operation will be described. When the temperature rise rate at which the temperature rises rapidly is high, the voltage (VA1) at the connection point (A1) between the first thermistor element 23 and the second thermistor element 24 is as shown in FIG.
As shown in D of FIG. When the voltage (VA1) becomes lower than the first reference voltage (VC), the output of the first comparator 30 becomes "H" level and a differential output is obtained.

In this case, it is detected that the temperature in the monitored area suddenly rises beyond a predetermined rate of temperature rise,
An alarm is issued by the differential output. Next, the voltage (VA) at the connection point (A) between the second thermistor element 23 and the resistor 24.
Is indicated by L in FIG. 2, and the second reference voltage (VB1) proportional to the voltage at the connection point (A2) between the first thermistor element 23 and the second thermistor element 24 is indicated by J in FIG. Is
When the voltage (VA) exceeds the second reference voltage (VB1),
The output of the second comparator 25 becomes "H" level, and a constant temperature output of 60 degrees is obtained.

In this case, as the second reference voltage (VB1), a voltage proportional to the voltage at the connection point (A2) between the first thermistor element 23 and the second thermistor element 24 is used as the second reference voltage (VB). Since the first thermistor element 23 having a slow thermal response has no deviation due to variations in the individual, the second thermistor element 24 having a fast thermal response can be eliminated.
The difference is due to the variation of the individual. Therefore,
The deviation (error) due to the variation of one thermistor element is small as shown by arrow N.

On the other hand, the voltage (V
When A) changes as shown by M in FIG. 2, the second reference voltage (VB1) also changes to the first thermistor element 23 and the second reference voltage (VB1).
2 in proportion to the voltage at the connection point (A2) of the thermistor element 24, as shown by K in FIG. Therefore, at the intersection O of M and K, a constant temperature output of 60 degrees can be obtained. Thus, even if the temperature rise rate is different, a constant temperature output can be obtained at 60 degrees, and the alarm temperature does not change. As a result, the accuracy of constant temperature output can be improved.

Next, FIG. 3 is a diagram showing another embodiment of the present invention. In this embodiment, the constant temperature output of the analog signal is converted into a digital signal. In FIG. 3, the voltage (VA) at the connection point (A) between the second thermistor element 24 and the resistor 26 is input to the A / D converter 37 provided in the CPU 36, and the first thermistor element 23 and the second thermistor element 23 are connected. A connection point (B) proportional to the voltage at the connection point (A2) of the thermistor element 24.
The second reference voltage (VB1) of 1) is used as the reference voltage (Vref) of the A / D converter 37.

Conventionally, the reference voltage (Vref) is constant, for example, 5V, and 256 bits are allocated to this 5V to obtain the A / D conversion output. In this embodiment, the reference voltage (Vref) changes in proportion to the voltage at the connection point (A2) between the first thermistor element 23 and the second thermistor element 24. For example, reference voltage (Vref)
Is changed to 3V, 256 bits are allocated to this 3V and A / D conversion is performed.

Therefore, the digitally converted constant temperature output has a small error and a high accuracy.

[0033]

As described above, according to the present invention, the second temperature detection element proportional to the connection point of the first temperature detection element having a slow thermal response and the second temperature detection element having a fast thermal response. Since the reference voltage is generated and the constant temperature output is obtained by comparing the second reference voltage with the voltage at the connection point of the second temperature detecting element and the resistor, the accuracy of the constant temperature output can be improved.

When the second reference voltage is input as the reference voltage of the A / D converter and the voltage at the connection point between the second temperature detecting element and the resistor is input to the A / D converter, the constant temperature is maintained. It is possible to obtain an accurate digital value as an output.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

[Fig. 2] Illustration of constant temperature output

FIG. 3 is a circuit diagram showing another embodiment of the present invention.

FIG. 4 is a circuit diagram showing a conventional example.

FIG. 5 is an operation explanatory diagram when the temperature rise rate is high.

FIG. 6 is an operation explanatory diagram when the temperature rise rate is low.

FIG. 7 is an explanatory diagram explaining a problem.

[Explanation of symbols]

21, 22: Connection terminal 23: First thermistor element (first temperature detecting element) 24: Second thermistor element (second temperature detecting element) 25, 28, 29, 33, 34: Resistor 26: Series Circuit 27: First reference voltage generation circuit (first reference voltage generation means) 30: First comparator 31: Second reference voltage generation circuit (second reference voltage generation means) 32: Buffer amplifier 35: Second comparator 36: CPU 37: A / D converter

Claims (4)

(57) [Claims] 1. A series circuit in which a first temperature detecting element having a slow thermal response, a second temperature detecting element having a fast thermal response, and a resistor are connected in series, and a first circuit generated by a first reference voltage generating means. 1 reference voltage,
A first comparator to which a voltage at a connection point between the first temperature detection element and the second temperature detection element is input, and a voltage at a connection point between the first temperature detection element and the second temperature detection element And a second comparator to which a second reference voltage proportional to the input voltage and a voltage at the connection point of the second temperature detection element and the resistor are input. 2. A second amplifier comprising a buffer amplifier connected to a connection point between the first temperature detecting element and the second temperature detecting element, and a pair of resistors connected in series to the buffer amplifier.
2. The heat sensor according to claim 1, wherein the second reference voltage is generated by the reference voltage generating means. 3. The heat sensor according to claim 2, wherein the buffer amplifier is not necessary when the resistance value of the pair of resistors is sufficiently large. 4. The second reference voltage is input as a reference voltage Vref of an A / D converter, and the voltage at the connection point between the second temperature detecting element and the resistor is input to the A / D converter. Any of claims 1 to 3 characterized in that
Heat detector according to.