JP2732671B2 - Heat detection method and heat detection circuit - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat detection method and a heat detection circuit for detecting an environmental temperature, for example, in a heat detector of a fire alarm device.

[Background / Prior Art] Conventionally, for example, in a fire alarm device or the like, in order to detect an environmental temperature for a fire determination, a thermistor and a resistor are connected in series by using a heat detecting element such as a thermistor whose resistance changes according to the temperature. A circuit is configured, power is applied to the series circuit, a change in the divided voltage due to a change in thermistor resistance value due to environmental temperature is monitored by a comparator or the like, and when a predetermined divided voltage is reached, a fire alarm is issued. The formula has been taken.

On the other hand, not only information on whether a predetermined partial pressure value, that is, a predetermined environmental temperature has been reached, but also, for example, transmitting all environmental temperatures to a central monitoring panel such as a fire receiver so as to make a fire judgment in a fire alarm device, for example. In such a case, the ambient temperature, that is, the analog divided voltage is separately provided by an MPU or the like.
A method of converting into digital information by a D conversion IC or the like is adopted.

[Problems to be Solved by the Invention] Providing a separate A / D conversion IC for digital conversion of environmental temperature is a problem in terms of component mounting and cost, and whether or not a predetermined environmental temperature is simply reached by a comparator or the like. Even in the case of detecting such a problem, a problem with the analog circuit is that stable temperature detection may occur due to variations in the components of the comparator and temperature characteristics. And stable information cannot be obtained.

Also, conventionally, as described in, for example, Japanese Utility Model Publication No. 48-551, Japanese Unexamined Patent Publication No. Sho 56-87831, a capacitor is connected to an impedance circuit including a thermistor, and a time constant based on the time constant of the CR circuit is used. A heat detection method for obtaining a temperature from a value has also been proposed. Also, as described in Japanese Utility Model Application No. 59-40760 (Japanese Utility Model Application Publication No. 60-152945), there is also a circuit that prepares a reference impedance circuit and obtains the temperature from the ratio between the heat measurement and the reference time. Proposed. However,
Since the circuit for the heat measurement and the circuit for the reference time are separately configured, it is necessary to provide wasteful circuit parts, which is not economical.

Means and Action for Solving the Problems In view of the above problems, the present invention forms a CR circuit by at least an impedance circuit including a heat detecting element and a capacitor, and determines an environmental value from a value related to a time constant of the CR circuit. The temperature is detected.

In particular, the first impedance circuit including the heat detection element includes the second impedance circuit configured by removing the heat detection element, thereby eliminating unnecessary circuit components.

Specifically, according to the present invention, in a heat detection method using a heat detection element whose resistance value changes with temperature, a capacitor is connected to at least a first impedance circuit including the heat detection element. A first CR circuit, a first value related to a time constant of the first CR circuit is obtained, and at least the heat detection is performed from the first impedance circuit. A second CR circuit is formed by connecting the capacitor to a second impedance circuit formed by removing the element, and a second value related to a time constant of the second CR circuit is obtained. A heat detection method is provided in which a ratio between a first value and a second value is obtained, and the temperature is known from the ratio.

As described above, according to the present invention, the environment temperature is measured by replacing it with a value related to the time constant, that is, a function of time. A / D conversion I even when transmitting
There is no need to provide C etc. separately.

Further, by using the impedance connected to the heat detecting element as the reference resistance, wasteful circuit components provided redundantly in the first and second impedance circuits are not required, and the cost can be reduced.

In addition, since the environmental temperature is measured by the ratio of the values related to the time constant, it is possible to measure the digital temperature from the beginning, and even when transmitting the entire environmental temperature,
A / D conversion IC is not required, and the quotient of the ratio between the values related to the time constant includes only the term of the resistance value, so it is not affected by the variation of other parts. As a result, a stable environmental temperature is obtained, and for example, a reliable fire judgment can be made from the result.

Further, according to the present invention, in a heat detection circuit using a heat detection element whose resistance value changes with temperature, a capacitor; a first impedance circuit including at least the heat detection element; A second impedance circuit comprising a part and configured by removing at least the heat detection element from the first impedance circuit; and forming a first CR circuit by connecting the capacitor to the first impedance circuit A second switching means for connecting the capacitor to the second impedance step to form a second CR circuit, and monitoring a voltage between both ends of the capacitor. Voltage monitoring means, time measurement means for measuring a time until the voltage monitoring means detects a certain value, the first CR First time related to the time constant of the road,
Control means for obtaining a ratio of the second CR circuit to a second time related to a time constant of the CR circuit, wherein the temperature can be obtained from the ratio. Is done.

As a result, the ambient temperature is measured with the ratio of the values related to the time constant, so it is possible to measure with a digital quantity from the beginning, and the A / D conversion IC can be used even when the entire environmental temperature is transmitted. Is unnecessary, and the quotient of the ratio between the values related to the time constant includes only the resistance value term, so that a stable environmental temperature can be obtained without being affected by the variation of other parts. Further, since the control means controls the first and second switching means and the time measuring means according to the determined sequence, the heat detection circuit can be operated with low current consumption. Therefore, it is effective, for example, as a heat detection circuit of a fire detector.

Example An example of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment in the case of a heat detector in which a value relating to a time constant of a CR circuit representing an environmental temperature is obtained when a capacitor is charged via an impedance circuit. 9 shows an embodiment in the case of a heat sensor in which a value relating to a time constant of a CR circuit representing an environmental temperature is obtained when a capacitor is discharged via an impedance circuit. In FIG. 1 and FIG.
Equivalent parts are indicated with the same reference numerals.

1 and 2, reference numeral 1 denotes a control means, that is, MP.
U, arithmetic unit 1a, read only memory (ROM) 1
b, a random access memory (RAM) 1c, an interface (I / F) 1d, and a counter 1e. 2 is a heat detecting element, 3 and 4 are resistors, and the heat detecting element 2 is a thermistor in this embodiment. The thermistor 2 and the resistors 3 and 4 together form a first impedance circuit, and the resistor 3 alone forms a second impedance circuit. The second impedance circuit is a thermistor 2 in the first impedance circuit.
And the resistor 4 are short-circuited, and are included as a part of the first impedance circuit. 5 is a capacitor,
6 is a comparator, 7 and 8 are resistors, and the comparator 6 and the resistors 7 and 8 together constitute voltage monitoring means. SW ₁ , SW ₂ , SW ₃ and SW ₄ are first, second, third and fourth switching means or switches, respectively, 9 is a clock generating circuit for generating a clock pulse to the counter 1 e, and E is Power supply.

Hereinafter, mainly the operation of FIG. 1 will be described with reference to FIG. 3A and FIG.
The operation of FIG. 2 will be described with reference to the flowchart of FIG. 3B, except that the charging operation and the discharging operation of the capacitor are only reversed, and the operation of obtaining the time constant is substantially the same. Then, in the operation of FIG.
Parts that differ from the figures are shown in parentheses.

The arithmetic unit 1a of the MPU 1 performs processing according to a program stored in the ROM 1b. First, the operation unit 1a is connected between the power source E and the capacitor 5 via the interface unit 1d (in FIG. 2, connected between the capacitor 5 and the ground).
₄ is turned on (step 302), and the capacitor 5 is charged (discharged in the case of FIG. 2). When the monitoring of the voltage or the charging (discharging in the case of FIG. 2) of the capacitor 5 to the predetermined voltage is completed after the lapse of the predetermined time (Y in step 303), the arithmetic unit 1a turns off the SW ₄ (step 304), At the same time, SW ₁ and SW ₃ are turned on (step 305). When SW ₁ is turned on, the charge stored in the capacitor 5 (the capacitor 5 is discharged in the case of FIG. 2), a first impedance circuit or thermistor 2, resistor 3, through the resistor 4 discharge ( In the case of FIG. 2, charging is started. Here, the resistor 4 has an effect of correcting the resistance value of the thermistor 2 that changes nonlinearly with temperature together with the resistor 3, but the resistor 4 is not always required.

One end of the capacitor 5 is connected to the input terminal of the comparator 6, and another input terminal of the comparator 6 is connected to SW ₃
Is turned on, a power supply divided by the resistors 7 and 8 is applied as a reference voltage. Operation unit 1a at the same time
Initializes the counter 1e for measuring the clock output of the clock generation circuit 9 (step 306). Discharge start (second
With the start of charging in the figure, the voltage across the capacitor 5 gradually decreases according to a time constant determined by the capacitance of the capacitor 5 and the combined resistance value of the thermistor 2, the resistor 3, and the resistor 4 (in the case of FIG. 2, To rise). At the same time, the counter 1e measures the elapsed time from the start of discharging (in the case of FIG. 2, the start of charging) by counting the number of input clocks from the clock generation circuit 9. The arithmetic unit 1a monitors the output state of the comparator 6 via the interface unit 1d together with the start of discharge (start of charging in the case of FIG. 2). After a lapse of a predetermined time, the voltage across the capacitor 5 decreases to the reference voltage (increases in FIG. 2), and as a result, the output of the comparator 6 becomes “H”.
→ "L" level or "L" → Invert to "H" level (Y in step 307). The arithmetic unit 1a stores the count value n of the counter 1e, which has counted the number of input clocks from the clock generation circuit 9 at the same time as detecting the above state change of the output of the comparator 6, in the RAM 1c (step 308).
The switches SW ₁ and SW ₃ are turned off (step 309). Control of the switch SW _3, the unnecessary when the reference voltage has the effect of reducing the current consumption by the resistor 7 and 8 by turning off the SW _3.

If the count value n is obtained as described above, the environmental temperature can be known from this value n. This will be described below using equations.

Power supply voltage value: E, Capacitor capacitance value: C, Clock frequency: f, Reference voltage value: Vr, Resistance value of resistance 3: R3, Resistance value of resistance 4: R4, Thermistor resistance value: TH, Thermistor, Resistance 3, If the count value of the counter 1e at the time of discharging (charging) the capacitor via the combined resistance value Z of the resistor 4 is n, then the combined resistance value Z of the thermistor 2, the resistor 3, and the resistor 4 is as follows: Z = R3 + R4 × TH / (R4 + TH) (Equation 1), and the reference voltage Vr of the capacitor 5 via the resistance value Z
Assuming that the discharge time (charge time) until is t1, Vr = E × exp (−t1 / C / Z)） t1 = −C × Z × ln (Vr / E) = n × 1 / f∴n = − f × C × Z × ln (Vr / E) (Equation 2) (In the case of FIG. 2, Vr = E × [1-exp (−t1 / C / Z)] ∴t1 = −C × Z × ln (1-Vr / E) = n × 1 / f∴n = −f × C × Z × ln (1−Vr / E) (Equation 2 ′)) As can be seen from (Equation 2), f, C, Vr,
Since the value of E is a constant, and the count value n is proportional to Z which is a function of the resistance value TH of the thermistor which changes with temperature, it is possible to know the environmental temperature from the count value n. Since this value n is a function of time and the count value of the clock pulse, the value representing the ambient temperature is
Since digital values are measured from the beginning, an A / D converter or the like for converting analog quantities into digital quantities is unnecessary even when the measured values are transmitted remotely.

However, the constants f, C, Vr, E
And the count value n depends on these constants. However, these constants are subject to environmental changes, power supply voltage changes, and aging changes. It is more preferable to use a value that does not.

Therefore, in the preferred embodiment of the present invention, the following processing is further performed.

That is, as described above, the operation unit 1a is
By turning on the switch SW ₄ via 1d (step 310) to charge the capacitor 5 (in FIG. 2 for discharge). After charging the capacitor 5 (after discharging in FIG. 2) (Y in step 311), the arithmetic unit 1a turns off SW ₄ (step 312), and at the same time,
Turns on the SW _2, SW ₃ (step 313). When SW ₂ is turned on, the electric charge charged in the capacitor 5 (the discharged capacitor in FIG. 2) starts discharging (charging in FIG. 2) via the resistor 3.

The input terminal of the comparator 6 receives the voltage of the capacitor 5
Reference voltage due to SW ₃ is turned on is applied. At the same time, the operation unit 1a initializes a counter 1e that measures the clock output of the clock generation circuit 9 (step 314).
With the start of discharging (and with the start of charging in FIG. 2), the voltage across the capacitor 5 gradually decreases (increases in FIG. 2) according to a time constant determined by the capacitance of the capacitor 5 and the combined resistance value of the resistor 3. . At the same time, the counter 1e measures the elapsed time from the start of discharge (the start of discharge in FIG. 2) by counting the number of input clocks from the clock generation circuit 9. The arithmetic unit 1a monitors the output state of the comparator 6 via the interface unit 1d at the start of discharging (at the start of charging in FIG. 2). After a lapse of a predetermined time, the voltage across the capacitor 5 decreases to the reference voltage (increases in FIG. 2). As a result, the output of the comparator 6 changes from “H” to “L” level or from “L” to “H” level. Reverse (step 315
Y). The arithmetic unit 1a stores the count value m of the counter 1e, which has counted the number of input clocks from the clock generation circuit 9, in the RAM 1c at the same time as detecting the state change of the output of the comparator 6 (step 316). The switches SW ₂ and SW ₃ are turned off (step 317).

Next, the arithmetic unit 1a calculates the count value m of the counter 1e at the time of discharging (charging in FIG. 2) via the resistor 3 which has just been measured,
A dividing process is performed on the count value n of the counter 1e at the time of discharging (charging in FIG. 2) via the previously measured combined resistance value Z (step 318). Then, the result of the division is transmitted to a fire receiver (not shown) via a signal line (step 31).
9) For example, make a fire decision. Note that a fire judgment based on the division result may be sent to a fire receiver or the like.

The environmental temperature can be obtained from the value of n / m obtained by the division process. The environmental temperature value obtained in this manner includes a capacitance error of the capacitor, a variation in the clock frequency of the clock generation circuit 9, Reference voltage errors due to component variations in 7 and 8 and elements due to errors in detected temperature values due to fluctuations in the power supply voltage E are not included. This will be described below using equations.

Assuming that the count value of the counter 1e at the time of discharging (charging) via the resistor 3 is m, and the discharging (charging) time until the capacitor 5 reaches the reference voltage via the resistor 3 is t0, Vr = E × exp ( −t0 / C / R3) ∴ t0 = −C × R3 × ln (Vr / E) = m × 1 / f∴m = −f × C × R3 × ln (Vr / E) (Equation 3) Becomes (In the case of FIG. 2, Vr = E × [1−exp (−t0 / C / R / 3))} t0 = −C × R3 × ln (1−Vr / E) = m × 1 / f m = -f * C * R3 * ln (1-Vr / E) (Equation 3 ') As described above, the count value n up to the reference voltage of the capacitor 5 via the combined resistance value Z is: n = −f × C × Z × ln (Vr / E) (Equation 2) Therefore, (in FIG. 2, n = −f × C × Z × ln (1−Vr / E) · ··· (Equation 2 ′) When the division processing is performed, n / m = Z / R3 = 1 + R4 × TH / R3 (R4 + TH) (Equation 4) The resistance is generally inexpensive, and even if a high-precision resistor is used, it is possible to minimize the increase in component price. Naturally, the same effect can be obtained even if the molecule is reversed.

In the above embodiment, the case where the resistor 3 is connected in series with the thermistor TH and the resistor 4 is connected in parallel to perform the variation correction of the count measurement value and the nonlinearity correction of the thermistor at the same time is shown. When the linearity correction is not required, it can be configured as shown in FIG. The division result in this case is as follows.

n / m = TH / R3 (Equation 5) In FIG. 2 in which a value related to the time constant is obtained at the time of charging the capacitor and the environmental temperature is known, the case where nonlinear correction of the thermistor is not required Is shown in FIG. 5, and the result of the division can be similarly expressed by (Equation 5).

Incidentally, a first view, FIG. 2, FIG. 4, and in Figure 5, the switch SW _4, in the case of FIGS. 1 and 2 is a sufficiently high resistance to the combined resistance value Z Resistance, fourth
In the case of FIG. 5 and FIG. 5, it is possible to replace the thermistor 2 and the resistor 3 with a resistor having a sufficiently high resistance value. In this case, the MPU, that is, the control means 1 needs to set the initial state of the capacitor before starting the measurement of the environmental temperature, that is, the charging state in the case of FIG. 1 and the discharging state in the case of FIG. You will have enough time.

[Effects of the Invention] As described above, according to the present invention, since the measurement is performed by replacing the environmental temperature with a value related to the time constant, that is, a function of time, the measurement can be performed with a digital quantity from the beginning. This eliminates the need for a separate A / D conversion IC to convert the measured value to a digital value even when transmitting the measured value to another location, and reduces the ratio between the values related to the time constant. As a result, there is an effect that a stable environmental temperature can be obtained without being affected by variations of other components.

A second CR circuit is provided by connecting the capacitor to a second impedance circuit which is part of a first impedance circuit and is configured by removing at least the heat detecting element from the first impedance circuit. And the second value related to the time constant of the second CR circuit is obtained by using the impedance (resistance) of the second impedance circuit as a reference resistance. There is an effect that cost reduction is realized as unnecessary.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a heat detection circuit according to an embodiment of the present invention, and shows a case where a value related to a time constant for measuring an environmental temperature is obtained when charging a capacitor. FIG. 2 is a circuit diagram showing a heat detecting circuit according to another embodiment of the present invention, and shows a case where a value related to a time constant for measuring an environmental temperature is obtained when discharging a capacitor. FIGS. 3A and 3B are flowcharts for explaining the operation of FIGS. 1 and 2, and FIGS. 4 and 5 are diagrams showing still another embodiment of the present invention. In the figure, 1 is an MPU (control means), 2 is a thermistor (heat detecting element), 3 and 4 are resistors, 5 is a capacitor, 6 is a comparator (voltage monitoring means), 9 is a clock generation circuit (time measuring means), SW _1, SW _2, SW _3, SW ₄ are first, second, third, fourth switching means, E is a power supply.

Claims (4)

(57) [Claims] 1. A heat detecting method using a heat detecting element whose resistance value changes with temperature, wherein a capacitor is connected to at least a first impedance circuit including the heat detecting element to form a first CR circuit. Determining a first value related to a time constant of the first CR circuit, comprising a part of the first impedance circuit and removing at least the heat detecting element from the first impedance circuit; A second CR circuit is formed by connecting the capacitor to a second impedance circuit, and a second value related to a time constant of the second CR circuit is obtained. A heat detection method in which a ratio of values is obtained, and the temperature is known from the ratio. 2. The method according to claim 1, wherein the first value is obtained by first charging the capacitor with a power supply voltage, and then discharging the capacitor through the first impedance circuit so that the voltage across the capacitor is reduced. The second value is likewise obtained by measuring the time to decrease to a first predetermined voltage value, the second value also charging the capacitor first with the power supply voltage, and then Is discharged through the second impedance circuit to measure the time required for the voltage across the capacitor to decrease to the first predetermined voltage value. The heat detection method described in the item. 3. The method of claim 1, wherein the first value discharges the capacitor first, and then charges the capacitor via the first impedance circuit so that the voltage across the capacitor becomes a second predetermined value. The second value is likewise obtained by measuring the time to reach a voltage, the second value being likewise firstly discharging the capacitor and then charging the capacitor via the second impedance circuit. 2. A heat detecting method according to claim 1, wherein said heat detecting method is obtained by measuring a time until a voltage between both ends of said capacitor reaches said second predetermined voltage. 4. A heat detection circuit using a heat detection element whose resistance value changes with temperature, comprising: a capacitor; a first impedance circuit including at least the heat detection element; and a part of the first impedance circuit. A second impedance circuit configured by removing at least the heat detecting element from the first impedance circuit; and a capacitor configured to connect the capacitor to the first impedance circuit to form a first CR circuit. First switching means, second switching means for connecting the capacitor to the second impedance circuit to form a second CR circuit, and voltage monitoring means for monitoring a voltage across the capacitor. Time measuring means for measuring a time until the voltage monitoring means detects a certain value; and a time constant of the first CR circuit. Control means for determining a ratio between a first time related to the second time and a second time related to the time constant of the second CR circuit, wherein the temperature can be obtained from the ratio. Characterized heat detection circuit.