JPS6311610B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in temperature difference detection devices used in fire detectors and the like.

The forward voltage drop (hereinafter referred to as "forward voltage") of the PN junction of a diode changes linearly over a wide temperature range when the forward direction current (hereinafter referred to as "forward current") is held constant. For this reason, diodes are widely used as stable and highly reliable temperature sensing elements. FIG. 1 shows an example of the forward voltage temperature characteristics of a diode. FIG. 2 shows an example of a conventional abnormal temperature rise detection device that utilizes the properties of this diode. In the same figure, 1 is a resistor R ₁ and a diode D ₁
The forward current is defined by the resistor _R1 . 2 is resistance R ₂ , variable resistance VR ₁ ,
A reference voltage generation circuit consisting of VR ₂ and a Zener diode VZ ₁ outputs predetermined voltages V ₁ and V ₂ close to the forward voltage V ₀ of the diode D ₁ . 3 is resistance R ₃ , R ₄ ,
An amplifier circuit consisting of amplifier _A1 , which outputs the output of detection section 1.
The difference between V ₀ and the output V ₁ of the reference voltage generation circuit 2 is amplified and output. 4 is a differentiator circuit consisting of a capacitor C ₁ and a resistor R ₅ , which outputs a voltage proportional to the rate of change of the output of the amplifier circuit 3. Reference numeral 5 denotes a comparator circuit consisting of an amplifier _A2 , which compares the output of the differentiating circuit 4 with another output _V2 of the reference voltage generating circuit 2, and outputs an output when the output of the differentiating circuit 4 exceeds _V2 . Reference numeral 6 denotes a switching circuit consisting of a thyristor SCR ₁ and resistors R ₆ and R ₇ , which is switched in accordance with the output of the comparator circuit 5 to activate the alarm 7 and generate an alarm. A time chart illustrating the operating state of this circuit is shown in FIG.

One of the problems with the abnormal temperature rise detection device configured as shown in Figure 2 is that the ratio of the voltage that changes with temperature to the forward voltage of the diode is small, so it is impossible to use a precision device that is not affected by temperature. This means that it is necessary to provide a reference voltage and amplify the difference between the reference voltage and the forward voltage of the diode. A reference voltage that is less affected by temperature can be obtained, for example, by using a temperature-compensated Zener diode, but such Zener diodes are generally expensive.

Another problem is that the forward voltage of a diode generally has a certain variation, and in order to absorb this variation, the reference voltage V ₁ must be adjusted for each sensor.

Furthermore, other problems can be raised, such as:
In order to detect the rate of temperature change, that is, the rate of temperature rise, a rate of change detection circuit such as a differential circuit is required. Generally, in order to effectively detect a fire, it is necessary to select the time constant of the differentiator circuit to be at least several minutes.To achieve such a time constant, a resistor with a large resistance value, a capacitor with a large capacitance, and a capacitor with a large resistance value are used. Is required. Furthermore, if such a large time constant is selected for the differentiating circuit, the time from when the power is turned on to the circuit until the circuit reaches a stable state will be approximately the same as the time constant of the differentiating circuit. This means that the temperature detection device does not operate until it reaches a stable state, which is a serious problem for devices such as fire detectors.

This invention was made in view of the above-mentioned problems, and eliminates the need for an amplifier circuit by using the PN junction of a transistor as a detection diode and amplifying the temperature change in its forward voltage with the transistor itself. In addition, by using two transistors with different thermal time constants and inserting resistors of approximately the same value between the emitters and the power supply of both transistors, the reference voltage generation circuit and differentiation circuit can be configured. The present invention is intended to provide a temperature difference detection device that is simple, inexpensive, and has a highly reliable abnormal temperature rise detection function.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 4 shows a circuit diagram of the embodiment. In the figure, a detection unit 1 is composed of two transistors Tr ₁ and Tr ₂ having substantially the same electrical characteristics and different thermal time constants, and resistors R ₁ to R ₁₁ . Assume now that the transistor Tr ₂ is configured to have a larger thermal time constant than the transistor Tr ₁ . Tr ₂ has its collector and base shorted and is used as a diode (diode connection). Comparison circuit 5
is composed of an N-gate thyristor SCR ₂ and resistors R ₁₂ to R ₁₄ , and outputs an output when the difference between the two outputs of the detection section 1 exceeds a certain value. The switching circuit 6 is composed of a thyristor SCR ₃ , which switches according to the output of the comparator circuit 5, activates the alarm 7, etc., and issues an alarm.

Next, the operation of the detection section 1 will be explained in detail. In general, two transistors Tr ₁ and Tr ₂ with the same characteristics are in the same environment, and their collector currents are I _{1 and} Tr 2, respectively.
When maintained at I ₂ , the difference between the base-emitter voltages V _BE1 and V _BE2 , which are the forward voltages of the PN junctions of each transistor, follows the relationship expressed by the following equation.

V _BE2 −V _BE1 = kT/qln(I ₂ /I ₁ ) (1) Here, k is Boltzmann constant, T is absolute temperature,
q is the electronic charge. Equation (1) is a general equation expressing the electrical characteristics of a PN junction diode. It is derived from this. In equation (2), Is
is the reverse saturation current of the PN junction, and V is the PN junction voltage. In the detection section 1, V _BE1 + I ₁ R ₁₀ = V _BE2 + I ₂ R ₁₁ (3) holds true, so Tr ₁ and Tr ₂ have the same characteristics and amplification factor.
hfe is sufficiently large and supply voltage (V ₊ −V _- ) = E
is sufficiently large, R ₈ + R ₉ ≫ R ₁₁ , and I ₂ is I ₂ ≒ E/
(R ₈ + R ₉ ), and if Tr ₁ and Tr ₂ are at the same temperature, using equation (1), ln (I ₂ / I ₁ ) = q/kT (I ₁ R ₁₀ −I ₂ R ₁₁ ) (4) Here, if R ₁₀ = R ₁₁ , I ₁ = I ₂ = E/R ₈ + R ₉ (5) In other words, I ₁ and I ₂ are equal and constant regardless of temperature. Become.

The temperature of transistor Tr ₁ is the same as that of transistor Tr ₂
When the temperature increases by a constant value △T (deg.), the following happens. At this time, the change in base-emitter voltage of Tr ₁ △V _BE1 is as follows: △V _BE1 = △V _BE1 ′(T) △T+V _BE1 ′(I ₁ ) △I ₁ = −C△T+kT/q △I ₁ /I ₂ (6) However, it is assumed that C=k/qln (I ₂ /I ₁ ), and that the difference between Tr ₁ and Tr ₂ is minute and only Tr ₁ is changing. T
is the temperature of transistor _Tr2 . Here, the constants determined by the transistor, I ₂ = I ₁₀ , I ₁ = I ₁₀ +
Let △I be ₁ .

Also, since the right side of equation (3) is constant, △V _BE1 + △I ₁ R ₁₀ = 0 (7) (6) and △V _BE1 is eliminated from equations (7), and △T and △I ₁ To find the relationship, △I ₁ = C△T/R ₁₀ (kT/I ₂ R ₁₀ q+1) = A・△T (8) When A creates a temperature difference between Tr ₁ and Tr ₂ , This is a quantity indicating a change in the collector current _I1 of _Tr1 due to a unit temperature difference. The temperature dependence of the coefficient A is determined by the first term of its denominator (kT/I ₂ R ₁₀ q), and has the property of decreasing as the temperature increases, but I ₂ (=I ₁₀ )
By appropriately determining and R ₁₀ (=R ₁₁ ) and keeping (I ₂ × R ₁₀ ) at an appropriate size, for example, the normal operating temperature range of a fire detector (0°C to 100°C; 273〓 to
373〓) can be minimized. Further, as will be described later, by appropriately selecting R ₁₀ and I ₂ to match the temperature characteristics of the detection element used in the comparison circuit 5, it is possible to reduce the temperature dependence characteristics of the detected temperature difference.

In equation (8), k and q are physically determined constants, k=1.38054×10 ^-23 (J・K ^-1 ), q
= 1.60210×10 ^-19 (C). For example, R ₁ = 5(K
Ω), I ₂ = I ₁₀ = 15 (uA), (R ₁ × I ₂ ) = 0.075, then the value of A at 0°C (273〓) is “1”.
When the temperature is 100℃ (373〓), the value of A is approximately 0.92. If (R ₁ × I ₂ ) = 0.06, 100℃ (373〓)
The value of A when is approximately 0.9. That is, (R ₁ ×
If I ₂ ) > 0.06, from 0℃ (273〓) to 100℃
The error in detecting temperature differences up to (373〓) can be kept within 10%. This error within 10% means
This is a sufficient value for a fire detector.

Next, the specific operation of the circuit shown in FIG. 4 will be explained. In the detection unit 1 in the figure, R ₇ = R ₈ , R ₁₀ =
Suppose that R is ₁₁ . Transistors Tr ₁ , Tr ₂
If the temperatures are the same, the collector currents I ₁ and I ₂ of each transistor are equal and constant regardless of temperature, as shown in equation (5). At this time, R ₇ =
If R ₈ , the voltage drop across each resistor
V ₁ and V ₂ are equal, the comparator circuit 5 does not produce an output,
Therefore, switching circuit 6 also does not operate. When the temperature changes slowly, such as a normal temperature change, the temperature of transistors Tr ₁ and Tr ₂ changes accordingly, and since the temperatures are equal, the device does not issue an alarm as described above. .

The operation when the temperature of the detection unit 1 suddenly rises due to a fire or the like is as follows. Tr ₁ is better than Tr ₂
Since the thermal time constant is smaller, the temperature of Tr ₁ rises following changes in the surrounding temperature, whereas the temperature of Tr ₂ follows the changes in the surrounding temperature more slowly because its thermal time constant is larger. . Therefore, a certain temperature difference occurs between Tr ₁ and Tr ₂ . This temperature difference causes the collector current I ₁ of Tr ₁ to increase according to equation (8). I ₁
As increases, the voltage drop V ₁ across resistor R ₇ increases,
Therefore, a potential difference occurs between V ₁ and V ₂ . When the potential difference exceeds a certain value, the comparison circuit 5 outputs an output, the switching circuit 6 switches, and the alarm 7
is activated and an alarm is issued. FIG. 5 shows a time chart explaining the above operation.

FIG. 6 shows another embodiment of the detection section according to the present invention. In correspondence with Fig. 4, the transistor Tr ₂
A constant current circuit 8 consisting of a field effect transistor FET and a resistor _R9 is inserted in series with the circuit. This constant current circuit 8 functions to eliminate fluctuations in I ₂ (=I ₁₀ ) due to fluctuations in circuit voltage (V ₊ −V ₋ =E) and stabilize the operation of the circuit.

Note that the above explanation assumes that the detection transistor is
This was done only for the NPN type, but of course
It is exactly the same even if a PNP type transistor is used.

In addition, in the above, the thermal time constant of transistor Tr ₂ was set large and used as a reference transistor, and the thermal time constant of transistor Tr ₁ was set small and used as a detection transistor, but the relationship between the thermal time constants was completely changed. Conversely, the transistor Tr ₁ may be used as a reference transistor and the transistor Tr ₂ may be used as a detection transistor. In this case, when the temperature of the transistor Tr ₂ increases, the collector current I ₁ decreases.

Next, the relationship between the detection section 1 and the comparison circuit 5 in FIG. 4 will be explained in detail. In the figure, an N-gate thyristor is used as the potential difference detection element of the comparator circuit 5.
Using SCR ₂ makes a lot of sense.
Figures 7a and 7b show the basic structure of an N-gate thyristor and its equivalent circuit. Thyristors are semiconductors with a PNPN structure, and there are two types: an N-gate type with a guard in the N layer in the middle, and a P-type with a gate in the P layer.
There is also a gate type. Although an N-gate type thyristor is shown in Fig. 7, a thyristor with such a structure is generally one in which the collectors and bases of a PNP type transistor α ₁ , an NPN type transistor, and a transistor α ₂ are interconnected. (Figure 7b). Now the gate (G)
Make the voltage equal to the anode (A) voltage so that no current flows through the gate, and connect the anode (A) with the positive and cathode
When a negative voltage is applied to (K), the voltage between N ₁ and P ₂ in Figure 7a becomes reverse biased, and the thyristor turns OFF. When the voltage of the gate (G) is gradually lowered in this state, a current flows between the anode (A) and the gate (G) through the PN junction between P ₁ and N ₁ . When this current exceeds a certain value, the thyristor turns on. Voltage between anode (A) and gate (G) at this time
V _AG is nothing but the base-emitter voltage V _BE 〓 ₁ of the transistor α ₁ shown in FIG. 7b.

As described above, the voltage drop across the PN junction when a constant current is applied varies linearly with temperature, as shown in FIG. 1, and its temperature coefficient is negative.
In other words, the anode/gate voltage V _AG to obtain the gate current I _G necessary to turn on the thyristor.
The gate-cathode voltage V _GK (in the case of the P-gate type) exhibits a temperature change similar to the characteristics shown in FIG.

The temperature characteristics of this V _AG (V _GK ) and the temperature characteristics of the output to the detection unit 1 shown in FIG. 4 or FIG. 6, that is, the collector current _{I 1} of the transistor Tr 1
The temperature characteristics of the change amount ΔI ₁ tend to decrease as the temperature of both partners increases, and by using these characteristics together, the detection error of the detection unit can be reduced.

Detection elements with such a PN junction include transistors in addition to thyristors. The purpose can also be achieved using a combination of diodes and comparators.

In the above explanation, the purpose of the device has been limited to detecting a sudden rise in temperature. However, with fire detectors, etc., even if the temperature rises gradually, the device detects a sudden rise in temperature when the temperature reaches a certain value. should raise an alarm. Such a request can be realized by the method described below.

That is, the so-called heat-sensitive thyristor is connected to the comparison circuit 5,
This is the method used in the switching circuit 6. Heat sensitive thyristors are PNPN like normal thyristors.
This is a device that takes advantage of the fact that the breakover voltage of a structured semiconductor changes with temperature. In other words, a heat sensitive thyristor has its anode
It has the characteristic of switching when the voltage between the cathodes exceeds the breakover voltage. FIG. 8 is a graph showing an example of the characteristics of a heat-sensitive thyristor. There are two types of heat-sensitive thyristors: N-gate and P-gate, and both operate in the same way. The switch temperature can be controlled by inserting a resistor between the anode and gate of the N-gate type heat-sensitive thyristor, and between the gate and cathode of the P-gate type heat-sensitive thyristor.
In the heat-sensitive thyristor having the characteristics shown in FIG.
For example, if the gate resistance R _GA is 1 (KΩ) and the power supply voltage is 20 (V), the breakover voltage will be less than the power supply voltage (20V) at about 70°C. In other words, the heat-sensitive thyristor under these conditions of use is
It has the characteristic of switching at 70℃.

On the other hand, a heat-sensitive thyristor has the same basic structure as a normal thyristor, and can be handled exactly like a normal thyristor below its switch temperature. That is, if a heat-sensitive thyristor set to switch at a certain predetermined temperature is used as elements SCR ₂ and SCR ₃ of the comparison circuit 5 or switching circuit 6 in FIG. The heat-sensitive thyristor operates as a rapid temperature rise detection device, and even if the temperature rise is gradual, when a predetermined temperature is reached, the heat-sensitive thyristor operates by itself to obtain a device that issues a signal or alarm. can.

As described above, the temperature difference detection device according to the present invention uses a physical phenomenon within a semiconductor as the detection principle, so it is highly reliable and has little variation between products. In other words, variations between products according to the present invention are caused by variations in the characteristics of the detection transistors Tr ₁ and Tr ₂ , and when using a constant current circuit, variations in the elements used (for example, FET). By checking the characteristics of the parts at the component stage and aligning the characteristics, there is no need for adjustments during assembly.

Furthermore, since the configuration is simple, there is little possibility of failure, and it is very inexpensive, making it extremely valuable in practice.

Further, in the temperature difference detection device according to the present invention, by changing the collector current flowing through the temperature difference detection transistor, it is possible to easily generate a signal similar to an abnormal temperature rise and perform an operation test.

To achieve this purpose, the resistance between the emitters of the two transistors Tr ₁ and Tr ₂ of the detection section 1 and the power supply is required.
It is most effective to change the ratio of R ₁₀ and R ₁₁ . A resistor in parallel with R ₁₀ as shown in Figure 9.
By providing a series circuit of R ₁₀ ' and a switch S and opening or closing the switch S manually or remotely, it is possible to test the operation of the device without increasing the temperature of the detection section. As the switch S, in addition to a mechanical type, a semiconductor element such as a transistor may be used.

Such an operation test method is safer and easier than the conventional method of directly heating the detection section with a heater, heat generating material, or the like. Conventional methods cannot be used, especially in hazardous areas where explosive gases are present.

Although the above explanation has focused on the abnormal temperature rise detection device, the basic function of the detection section of the present invention is to detect a temperature difference, and the thermal time constants of the two detection transistors of the detection section are equalized. However, if it is placed at two distant points, it can be used as a device to detect the temperature difference between the two points. Furthermore, when used in combination with a switching circuit, it can be used as a device for keeping the temperature between two points constant, for example, as a control device for air conditioning equipment that keeps the outside temperature and indoor temperature in a constant relationship. Furthermore, the abnormal temperature rise detection device can be applied not only as a fire detector but also as a control device for preventing overheating of electrical appliances.

[Brief explanation of the drawing]

Figure 1 is a temperature characteristic diagram of a diode, Figure 2 is a circuit of a conventional abnormal temperature rise detection device, and Figure 3 is a diagram of a conventional abnormal temperature rise detection device.
4 is a circuit diagram of one embodiment of the present invention. FIG. 5 is a time chart of the circuit of FIG. 4. FIG. 6 is a circuit diagram of another embodiment of the invention. 7a and 7b show the basic structure and equivalent circuit of an N-gate thyristor, FIG. 8 shows a characteristic diagram of a heat-sensitive thyristor, and FIG. 9 shows an operation test circuit of the present invention. Note that the same reference numerals indicate the same or equivalent parts. 1: Detection section, 2: Reference voltage generation circuit, 3: Amplification circuit, 4: Differential circuit, 5: Comparison circuit, 6: Switching circuit, 7: Alarm, 8: Constant current circuit.

Claims (1)

[Claims] 1. The base of a diode-connected second transistor with a defined forward current is connected to the base of a first transistor having electrical characteristics similar to those of the second transistor; One of the first and second transistors is set as a reference, and the other is set as a measurement, and the thermal time constants of the transistors are different from each other, and the first transistor is connected between the power supply and the emitter of the first transistor. A resistor is inserted, and a second resistor is further inserted between the power supply and the emitter of the second transistor, and the resistance values of the first and second resistors are set to be approximately the same value, and the collector of the first transistor is A temperature difference detection device, characterized in that a temperature difference between the second transistor and the first transistor is detected from a change in current. 2. The temperature difference detection device according to claim 1, wherein a constant current circuit is provided in series with the second transistor. 3 The product of the resistance value of the first or second resistor and the collector current of the first or second transistor is
The temperature difference detection device according to claim 1 or 2, wherein the temperature difference is 0.06 (Ω·A) or more. 4. A patent claim in which a comparison circuit is provided that outputs an output when the difference between the collector current of the second transistor and the collector current of the first transistor exceeds a predetermined value, and the comparison circuit uses a switching element having a PN junction. The temperature difference detection device according to any one of the first and second ranges.