JPH0533438B2 - - Google Patents

Description

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

[Background technology]

To explain the basic configuration of this type of differential heat sensor, as shown in Figure 4, thermistors TH1 and TH2 have different response characteristics (thermal response characteristics are
TH1 is fast and TH2 is slow) connected in series, and two resistors R.
1, a second series circuit 1 formed by connecting R2 in series.
00b to form a heat detection bridge circuit 100,
The connection point V1 of each of these two series circuits 100a, 100b in response to a change (increase) in ambient temperature.
Comparison circuit 101 compares voltage level fluctuations occurring at V2
The configuration is such that when the output level changes, the switching means 102 is driven to output an alarm signal.

To explain the operation of this sensor, a thermistor
If the same B constant and resistance value are used for TH1 and TH2, V1 will be approximately 1/2V when there is no change in the ambient temperature.
(Here, V is the supply voltage from the power supply circuit 103), and at this time, V2 is set by resistors R1 and R2 so that V2>V1 is satisfied.
Since the value of is set, the output of the comparator circuit 101 becomes "L" level and the SCR 102 is not triggered. The relay will not operate and therefore will not generate an alarm signal. Also,
If the ambient temperature rises slowly, use a thermistor.
Since the resistance values of TH1 and TH2 gradually change, V1
does not change, the condition of V2>V1 is maintained, and the comparator circuit 101 maintains the "L" level, so similarly
SCR 102 is not triggered.

However, when the ambient temperature rises rapidly,
Since the resistance value of only thermistor TH1 becomes small, V1 rises and becomes V1>V2, and as a result, the comparator circuit 101 is inverted to "H" level and the SCR102
, the relay on the receiver (not shown) side is also driven to generate an alarm signal.

Also, the one shown in Figure 5 is the thermistor TH
and resistor R3 form a first series circuit 100a,
The second series circuit 100b is formed by connecting a resistor R4 and a capacitor C1 in series, and further connects the connection point of the first series circuit 100a and the second series circuit 100b.
The heat detection bridge circuit 100 is constructed by connecting a diode D1 between the connection points of the first and second connection points so that its cathode is connected to the first connection point.

With this configuration, when there is no change in the ambient temperature, the capacitor C1 of the second series circuit 100b is charged via the resistor R4, and V2 becomes V2=
V1 + Vf (here, Vf is the voltage drop of diode D1, which is approximately 0.6V in the case of a silicon diode)
Therefore, V2>V1, the comparator circuit 101 becomes "L" level, and the SCR 102 is not triggered.

Also, when the ambient temperature changes slowly, the resistance value of the thermistor TH gradually decreases, and at this time, the capacitor C1 is sufficiently charged by the resistor R4 to maintain the condition of V2 = V1 + Vf. SCR is not triggered.

However, when the ambient temperature rises rapidly,
V1 rises, and at this time the voltage V2 of capacitor C1
However, since the charging current flowing into the capacitor C1 is limited by the resistor R4, V1>V2 finally becomes, and the output of the comparator circuit 101 is inverted to the "H" level and the SCR 102 is triggered. This drives the relay on the receiver (not shown) side and generates an alarm signal.

However, in such a differential heat sensor, especially the type shown in Figure 4, it is extremely difficult to set the thermal response characteristics of the thermistors TH1 and TH2 in the first series circuit, and the manufacturing cost is high. However, the type shown in Figure 5 has problems such as being expensive.
When the power supply to the SCR 102 is cut off to restore the sensor, it takes a considerable amount of time for the thermal detection bridge circuit 100 to detect a thermal change and restart. For this reason, when used in connection with a storage type receiver that has been developed in recent years from the perspective of preventing alarms in non-fire situations, there is a risk of missing alarms as the power is repeatedly cut off during the cancel time. It was hot.

[Purpose of the invention]

The present invention was made in view of the above circumstances, and
The purpose of the present invention is to provide a differential heat sensor configured to ensure re-operation and eliminate false alarms even if the power supply from the power circuit is cut off during a reset operation on the receiver side. .

[Disclosure of the invention]

In order to achieve the above object, the present invention proposes a connection point of a first series circuit in which thermistors having different thermal responses are connected in series, and a second series circuit in which a resistor and a capacitor are connected in series. A heat detection bridge circuit is formed by connecting the connection points with diodes, and a charge storage capacitor is connected in parallel to this bridge circuit. The comparison circuit compares the voltage levels generated at the two connection points of the bridge circuit, and when the output level changes, the switching means is driven to output an alarm signal, and the power supply voltage supplied from the power supply circuit to the switching means is In a differential heat sensor configured to supply the charging voltage of the charge storage capacitor to the heat detection bridge circuit after the sensor is restored by shutting off the power, in particular, the voltage of the heat detection bridge circuit is When the detected voltage drops to a predetermined level, the capacitor provided in the second series circuit is rapidly charged to raise the voltage at the connection point of the second series circuit to the power supply level. .

〔Example〕

An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows the circuit configuration of an embodiment of the present invention. 1 is a heat detection bridge circuit, which includes a thermistor TH1 and has the same B constant and resistance value as the thermistor TH1, but has a thermal response. It consists of a very slow temperature compensation thermistor TH2 connected in series, and this thermistor TH2 has a resistance value of TH1 =
TH2, V1=1/2V (where V is the output of the power supply circuit 3), and V1 is always kept constant.

The first series circuit 1a and the second series circuit 1b are connected in parallel, and the first and second series circuits 1a and 1b are connected in parallel.
A diode D1 is connected between the connection point of the first series circuit 1a and the cathode of the diode D1 is connected to the connection point of the first series circuit 1a.

Note that 2 is a comparison circuit that compares the voltage levels of voltages V1 and V2 at the connection point of the heat detection bridge circuit 1, and 3 is a comparison circuit that compares the voltage levels of the voltages V1 and V2 at the connection point of the heat detection bridge circuit 1. 4 is a switching means.
Thermal detection bridge circuit 1 configured in this way
is provided with a voltage holding circuit 5, which connects a charge storage capacitor C2 in parallel to the thermal detection bridge circuit 1, and connects a charge storage capacitor C2 between the thermal detection bridge circuit 1 and the power supply circuit 3. Diode D
2 are connected such that their cathodes are on the heat detection bridge circuit 1 side.

The basic operation is the same as that of the sensor shown in FIG.
When power is supplied, a constant voltage is supplied to the heat detection bridge circuit 1 via the power supply circuit 3, and at the same time, the capacitor C2 is charged. Furthermore, when the voltage between L and C is cut off by the receiver reset operation, the discharge of the electric charge charged by the diode D2 is prevented, so if the capacitance of the capacitor C2 is set appropriately, the receiver Even after the reset operation, the voltage supplied to the thermal detection bridge circuit 1 is maintained by the charging voltage of the capacitor C2. Therefore, after the power supply voltage is supplied to the thermal detection bridge circuit 1 via the power supply circuit 3 after the reset operation, the thermal detection bridge circuit 1 can immediately detect a change in the ambient temperature and operate the switching means 4.

FIG. 2 shows the operation of the differential heat sensor of the present invention.

V is the power supply voltage, V1 and V2 are the connection point voltages of the first and second series circuits of the thermal detection bridge circuit, C2 is the charge storage capacitor, ZD is the Zener voltage that is the reference voltage of the comparator CP, and the capacitor C
A comparator CP and a diode D3 are provided to quickly charge the battery.

According to such a differential heat sensor of the present invention,
When the power is turned on, the voltage of the thermal detection bridge circuit which is the input voltage of the comparator CP, that is, the voltage of the charge storage capacitor C2, is much smaller than the Zener voltage ZD, so the input voltage of the comparator CP
turns on immediately, capacitor C1 is rapidly charged, and V2 rises to a level close to the supply voltage. Then, V2>V1, and the output of the comparator circuit 2 becomes "L". Therefore, the thyristor 4 is not turned on when the power is turned on.

Note that the wavy lines indicate comparator CP and diode D.
3 shows the change in the voltage level of V2 in the case where there is no rapid charging means for the capacitor C1. In such a case, after the power is turned on, V2 < V1, and malfunction cannot be prevented as it is.

After the power is turned on, the charge storage capacitor C2 connected in parallel to the heat detection bridge circuit continues to charge, and when it exceeds the Zener voltage ZD, the comparator CP is turned off, and from then on, the capacitor C1 is discharged, so the voltage of C1 decreases. I'll go.

On the other hand, when the voltage of the heat detection bridge circuit becomes V2<V1 due to a sudden rise in ambient temperature, the output of the comparator circuit 2 is inverted to the "H" level and the thyristor 4 is turned on.

When this turn-on operation is determined on the receiver side, the receiver disconnects sensor A from the power supply line, performs a reset, and connects sensor A to the power supply line again in order to perform an accumulation operation.

The change in voltage level in this case is shown in Figure 3, and according to the differential sensor of the present invention, there is a rise in ambient temperature when the sensor is reconnected to the power line after being reset. In this case, the condition of V1>V2 is maintained, and a prompt alarm operation can be performed after recovery.

In this embodiment, the capacitor C1 of the second series circuit 1b is charged preferentially until the capacitor C2 of the voltage holding circuit 5 is sufficiently charged.
CP uses the Zener voltage of the Zener diode ZD installed on the output side of the power supply circuit 3 as a reference voltage, and uses the voltage of the bridge circuit 1, that is, the voltage of the capacitor C2, as a comparison input, and when the power is turned on, the comparison input drops below the reference voltage level. When this happens, the capacitor C1 can be rapidly charged via the diode D3.

[Effects of the Invention] As understood from the above explanation, according to the differential heat sensor of the present invention, the voltage of the heat detection bridge circuit is maintained even after the power is cut off by a reset operation. Reactivation after a reset operation is quickly performed. Therefore, even when used in connection with a storage type receiver, there is no fear of missing alarms, and a highly reliable differential heat sensor can be realized.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention;
FIGS. 2 and 3 are time charts showing the operation of the differential heat sensor of the present invention, and FIGS. 4 and 5 are circuit diagrams of a conventional differential heat sensor. (Explanation of symbols), A...Differential heat sensor of the present invention,
1...Thermal detection bridge circuit, 1a...The first series circuit, 1b...The second series circuit, 2...
Comparison circuit, 3...power supply circuit, 4...switching means, 5...voltage holding circuit.

Claims (1)

[Claims] 1. A connection point of a first series circuit in which thermistors having different thermal responses are connected in series and a connection point in a second series circuit in which a resistor and a capacitor are connected in series are connected by a diode. A heat detection bridge circuit is formed by connecting a charge storage capacitor to this bridge circuit in parallel, and when a constant power supply voltage is supplied from the power supply circuit, the two connections of the bridge circuit are connected due to changes in ambient temperature. A comparison circuit compares the voltage levels occurring at the points, and when the output level changes, the switching means is driven to output an alarm signal, and the power supply voltage supplied from the power supply circuit to the switching means is cut off to activate the sensor. In a differential heat sensor configured to supply and hold the charging voltage of the charge storage capacitor to the heat detection bridge circuit after restoration, when the voltage of the heat detection bridge circuit drops to a predetermined level, A differential heat sensor configured to quickly charge a capacitor provided in the second series circuit to rapidly raise the voltage level at the connection point of the second series circuit to a power supply voltage level.