JPH0626962A - Differential pressure detecting device - Google Patents

Abstract

PURPOSE:To surely detect even a minute differential pressure, ensure a stable operation, reduce size and cost, further, eliminate a trouble such as contact failure, and enhance durability and reliability. CONSTITUTION:A differential pressure between a first space Px and a second space Py is detected. A differential pressure detecting device has a housing 2 internally having an air passage S having one end Sx facing the first space Px and the other end Sy facing the second space Py; a detecting thermistor 4 arranged in the air passage S to detect an air flow H running in the air passage S by the differential pressure between the first space Px and the second space Py; and a signal processing circuit 3 for processing a detection signal Sd based on the detecting thermistor 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a differential pressure detecting device suitable for detecting clogging of a filter provided in a ventilation fan in a kitchen.

[0002]

2. Description of the Related Art A conventional differential pressure detecting device is shown in FIG. In the figure, a differential pressure detector 70 is provided with a first pressure acting space 72 and a second pressure acting space 73 inside a housing 71, and each pressure acting space 72 and 73 is a diaphragm 74 formed by a thin plate. Partitioned by. In addition, a pair of terminals 75 and 76, one end of which is led to the outside, are faced inside the second pressure acting space 73, and one terminal 75 has the fixed contact 7
5s is provided, and the other terminal 76 is provided with a movable piece 76p having a movable contact 76s at the tip. At this time, the movable contact 76s is arranged so as to be in contact with the fixed contact 75s. In addition, the transmission pin 7 provided at the intermediate position of the movable piece 76p.
8 is brought into contact with the diaphragm 74.

Therefore, when the differential pressure of the first pressure acting space 72 with respect to the second pressure acting space 73 is less than a predetermined value, the movable contact 76s contacts the fixed contact 75s due to the elasticity of the movable piece 76p. When the differential pressure exceeds a predetermined value, the diaphragm 74 is displaced toward the second pressure acting space 73 side and the transmission pin 78 is pushed to separate the movable contact 76s from the fixed contact 75s. That is,
Switch from the ON state to the OFF state.

In the case of such a differential pressure detecting device 70, since the diaphragm 74 used is formed of a thin flat plate, its displacement amount changes continuously in proportion to the magnitude of the differential pressure. However, the preferable opening characteristic of the contact cannot be obtained. For this reason, snap-action diaphragms are also used.
It is known from Japanese Patent Publication No. 4-29807.

[0005]

However, the conventional differential pressure detecting device including the above-mentioned differential pressure detecting device 70 has the following problems to be solved.

First, the differential pressure to be detected is 10 to 30 Pa.
In the case of (approximately 1~3mmH ₂ 0) about the micro pressure, for increasing the diaphragm area, or do not decrease it can not be expected reliable operation, with the entire apparatus is increased in size,
Increases costs. On the other hand, when the diaphragm is made thin, it becomes difficult to keep the diaphragm flat, and eventually the operation becomes unstable such as partial snap operation.

Second, since the electrical contacts are exposed in the pressure acting space, gas and oil components are detected, especially when used for detecting filter clogging in a domestic ventilation fan often installed in the kitchen. Adhesion may cause stains to occur easily, and operation may be disabled due to poor electrical contact.

The present invention has solved the problems existing in the prior art as described above, and can reliably detect even a small differential pressure, guarantee stable operation, and reduce the size and cost. Furthermore, another object of the present invention is to provide a differential pressure detecting device capable of enhancing durability and reliability by eliminating adverse effects such as poor contact.

[0009]

The present invention provides a first space Px.
Differential pressure detection device 1 for detecting the differential pressure between the second space Py and the second space Py
When configuring the above, the housing 2 having the air passage S therein, one end Sx of which faces the first space Px and the other end Sy of which faces the second space Py, is disposed in the air passage S, and A detection thermistor 4 for detecting the air flow H flowing in the air passage S by the pressure difference between the first space Px and the second space Py.
And a signal processing circuit 3 for processing the detection signal Sd based on the detection thermistor 4.

In this case, the correction thermistor 5 may be arranged in the space Pw which is not affected by the air flow H of the ventilation passage S, and the bridge circuit 7 including the correction thermistor 5 and the detection thermistor 4 may be constructed. desirable. The space Pw can be formed in the housing 2 by branching from the ventilation path S in a substantially right-angled direction. In addition, the signal processing circuit 3 is connected to the output side of the bridge circuit 7 to correct the temperature characteristics of the bridge circuit 7, and the correction circuit includes one or more diodes 9 and 10 and a series circuit 12 of a resistor 11. It is desirable to provide the circuit 8.

[0011]

According to the differential pressure detecting device 1 of the present invention, the air passage S provided inside the housing 2 has one end Sx facing the first space Px and the other end Sy facing the second space Py. Therefore, when no pressure difference is generated between the first space Px and the second space Py, air does not flow in the ventilation path S. Therefore, the detection thermistor 4 is not cooled. In this case, the air passage S
If the correction thermistor 5 is arranged in the space Pw that is not affected by the air flow H, and the bridge circuit 7 is configured, the correction thermistor 5 and the detection thermistor 4 have substantially the same ambient temperature. Therefore, the unbalanced output voltage (detection signal Sd) of the bridge circuit 7 becomes substantially zero. That is, no differential pressure is detected.

On the other hand, when a pressure difference is generated between the first space Px and the second space Py, an air flow H flowing from the higher pressure side to the lower pressure side is generated in the air passage S, and the detection thermistor 4 is generated. Only is cooled. As a result, an unbalanced output voltage (detection signal Sd) appears in the bridge circuit 7, and the differential pressure is detected.

At this time, the temperature characteristic of the bridge circuit 7 is corrected by providing the correction circuit 8 including the series circuit 12 of the diodes 9 and 10 and the resistor 11 on the output side of the bridge circuit 7. That is, the ambient temperature rises and the bridge circuit 7
When the detection signal Sd of No. 2 becomes small, the forward minimum voltage that causes a current to flow through the diodes 9 and 10 in the correction circuit 8 also becomes low, and the temperature characteristic of the bridge circuit 7 is corrected. Therefore, even when it is installed in a place such as a kitchen where the temperature changes drastically, the differential pressure can always be detected accurately, and stability and reliability are enhanced.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, preferred embodiments according to the present invention will be described in detail with reference to the drawings.

First, the structure of the differential pressure detecting device 1 according to the present invention will be described with reference to FIGS.

As shown in FIGS. 1 and 2, the differential pressure detecting device 1 includes a housing 2 which is formed in a rectangular parallelepiped shape as a whole.
Inside the housing 2, a ventilation path S having a relatively small diameter is formed so as to penetrate in the width direction. In this case, the connection ports 21x and 21y protruding outward are attached to both side surfaces of the housing 2. As a result, the air passage S penetrates through the connection ports 21x and 21y, the tip opening of the one connection port 21x serves as one end Sx of the air passage S, and the tip opening of the other connection port 21y extends. Is the other end Sy.

A board housing recess 22 for housing the printed board E is formed on the outer surface of the housing 2 which is parallel to the ventilation path S. Furthermore, one rectifying recess 23 and two thermistor receiving recesses 2 are provided in the substrate receiving recess 22.
4 and 25 are sequentially formed along the air passage S at positions including the air passage S, respectively. As a result, the ventilation path S communicates with the flow regulating recess 23 and the accommodation recesses 24 and 25. The thermistor housing recess 24 located in the middle is a space Pw branched from the air passage S in a direction perpendicular to the air passage S. Is formed deeper and the projection recesses 26, which reliably prevent the influence of the air flow, are provided at intermediate positions of the accommodation recess 24. Further, a component housing recess 27 is provided at another position of the board housing recess 22. A part of the component mounted on the printed board E is accommodated in the component accommodating recess 27 when the printed board E is attached to the substrate accommodating recess 22.

The detection thermistor 4 is disposed on the air passage S inside the thermistor housing recess 25, and at a position inside the thermistor housing recess 24 that is not affected by the air flow in the air passage S. The correction thermistor 5 is arranged inside the space Pw. On the other hand, the thermistors 4 and 5 are connected to the signal processing circuit 3 shown in FIG.
The signal processing circuit 3 is mounted on the printed circuit board E.

Next, a specific configuration of the signal processing circuit 3 will be described. First, the signal processing circuit 3 has resistors 31 and 32, and the resistors 31 and 32 and the thermistors 4 and 5 form a bridge circuit 7. A DC voltage source 33 is connected to the connection point xa between the resistors 31 and 32 and the connection point xb between the thermistors 4 and 5 in the bridge circuit 7, and the connection point xc between the resistor 31 and the thermistor 4 is connected to the comparator 34.
The connection point xd of the resistor 32 and the thermistor 5 is connected to the non-inverting input section of the comparator 34 via the two diodes 9 and 10 connected in series. A resistor 11 is connected between the inverting input section and the non-inverting input section of the comparator 34. Therefore, the series circuit 12 is composed of the two diodes 9, 10 and the resistor 11,
This series circuit 12 serves as a correction circuit 8 and binarizes the output of the bridge circuit 7 by utilizing the voltage characteristics of the diodes 9 and 10 in the forward direction. Function as a digitalization circuit.

Furthermore, the output of the comparator 34 is connected to the base of the transistor 35. On the other hand, the DC voltage source 33 is connected to the power input port of the comparator 34, and the resistor 36 and the light emitting diode (alarm) 3 are connected.
7 is connected to the collector of the transistor 35 via a series circuit, and the negative side of the DC voltage source 33 is grounded, and the ground port of the comparator 34 and the transistor 3 are connected.
The emitter of 5 is grounded.

Next, the usage and operation of the differential pressure detecting device 1 (clogging detecting device) according to the present invention will be described with reference to FIGS.

As shown in FIG. 7, the differential pressure detecting device 1 is attached near the ventilation fan M installed on the wall W of the house. Accordingly, it can be used as a clogging detection device for the filter Fi provided on the indoor side of the ventilation fan M. In this case, one end Sx of the ventilation path S faces the indoor side that is the first space Px, and the other end Sy is between the fan Fa and the filter Fi in the ventilation fan M that is the second space Py via the tube 51. To face.

On the other hand, the differential pressure detecting device 1 operates as follows. First, a constant voltage is applied to the bridge circuit 7 from the DC voltage source 33, and the thermistors 4 and 5 generate heat by flowing current. The resistors 31 and 32 function as current limiting resistors. Therefore, the temperature of the thermistors 4 and 5 is stable at the point where the energy of natural heat dissipation and the energy of self-heating are balanced by the heat dissipation coefficient.

When the filter Fi is normal, since the air resistance of the filter Fi is small, the second space Py
The pressure in (the space on the fan Fa side of the filter Fi) is close to the atmospheric pressure, and the differential pressure between the second space Py and the first space Px (inside space) remains relatively small. The differential pressure in this case is usually less than 3 mmH ₂ O. Therefore, since air does not flow in the air passage S provided in the housing 2, the ambient temperatures of the detection thermistor 4 and the correction thermistor 5 become substantially the same, and the bridge circuit 7 is balanced. Therefore, the unbalanced output voltage at the connection points xc and xd in the bridge circuit 7, that is, the detection signal Sd becomes zero. As a result, the input voltage of the comparator 34 is zero, the transistor 35 is turned off, and the light emitting diode 37 is not turned on.

On the other hand, when the filter Fi is used to contaminate and become clogged, the air resistance of the filter Fi increases, and the negative pressure in the second space Py also increases. As a result, the pressure difference between the second space Py and the first space Px becomes large, and an air flow H flowing from the indoor space is generated in the ventilation path S. Therefore, since only the thermistor 4 for detection is cooled, the connection points xc and x of the bridge circuit 7
A detection signal Sd which is an unbalanced output voltage is generated between d,
This detection signal Sd is given to the correction circuit 8. As a result, a current flows through the diodes 9 and 10 and the resistor 11, and the terminal voltage of the resistor 11 is applied to the comparator 34.
The transistor 35 is turned on by the output voltage of the comparator 34, the light emitting diode 37 is turned on, and the clogging is notified.

By the way, the correction circuit 8 functions as follows. Generally, the resistance value R ₁ of the thermistor is R ₁ = R ₂ ex
pB (1 / T ₁ −1 / T ₂ ) (where R ₁ is the absolute temperature T ₁
Since the temperature characteristic is based on the resistance value at [K], R ₂ is the resistance value at absolute temperature T ₂ [K], and B is the B constant of the thermistor), the higher the temperature, the smaller the resistance change rate with respect to temperature. Become. Therefore, if the cooling amounts of the two thermistors 4 and 5 of the bridge circuit 7 are different, the difference in the resistance values of the thermistors 4 and 5 also becomes large, and this appears as the magnitude of the unbalanced output potential in the bridge circuit 7. The magnitude of this unbalanced output potential is as shown in FIG.
It decreases as the ambient temperature increases.

On the other hand, since the current does not flow in the diode unless it exceeds a certain minimum voltage even in the forward direction, when the unbalanced output voltage of the bridge circuit 7 is equal to or lower than the minimum voltage, the diodes 9 and 10 are not connected. No current flows. Further, the diode generally has the temperature characteristics shown in FIGS. 5 and 6, and exhibits the same tendency as the temperature characteristics of the bridge circuit 7 shown in FIG. Therefore, when a certain amount of current flows through the diodes 9 and 10, the diodes 9 and 10 serve as a temperature sensitive resistor and divide the voltage with the resistor 11. When the ambient temperature rises, the resistances of the diodes 9 and 10 decrease and the terminal voltage of the resistance 11 increases. However, in this case, since the unbalanced output voltage of the bridge circuit 7 is lowered, each of them eventually acts in the direction of canceling each other. Therefore,
The temperature characteristic of the bridge circuit 7 is corrected. In this case, a correction characteristic suitable for the bridge circuit 7 can be obtained by arbitrarily selecting the type, quantity, resistance value, etc. of the diodes.

The embodiment has been described in detail above.
The present invention is not limited to such an embodiment,
The detailed configuration, shape, quantity, etc. can be arbitrarily changed without departing from the scope of the present invention.

[0029]

As described above, according to the present invention, in the differential pressure detecting device for detecting the differential pressure between the first space and the second space, one end faces the first space and the other end is the second space. A housing having a ventilation passage facing the space of, and arranged in the ventilation passage,
And since the detection thermistor for detecting the air flow flowing in the ventilation path by the pressure difference between the first space and the second space, and a signal processing circuit for processing the detection signal based on the detection thermistor are provided, the following It has a remarkable effect.

A minute differential pressure can be reliably detected, stable operation can be guaranteed, and downsizing and cost reduction can be achieved.

Since the thermistor is externally sealed, there is no risk of electrical contact failure due to dirt or the like, and durability and reliability can be dramatically improved, especially for household use. It is most suitable for the detection of filter clogging in a ventilation fan.

[Brief description of drawings]

FIG. 1 is a partial sectional front view of a differential pressure detection device according to the present invention,

FIG. 2 is a sectional view taken along line AA in FIG.

FIG. 3 is an electric circuit diagram of the differential pressure detection device,

FIG. 4 is a characteristic diagram of unbalanced output voltage vs. ambient temperature of a bridge circuit in the differential pressure detector.

FIG. 5 is a forward voltage vs. forward current characteristic diagram in which the ambient temperature of the diode in the correction circuit of the differential pressure detection device is used as a parameter,

FIG. 6 is a characteristic diagram of forward voltage vs. ambient temperature of a diode in the correction circuit,

FIG. 7 is a partial cross-sectional side view showing a state in which the differential pressure detection device is attached to a ventilation fan,

FIG. 8 is a vertical sectional side view of a differential pressure detecting device according to a conventional technique,

[Explanation of symbols]

 1 differential pressure detection device 2 housing 3 signal processing circuit 4 detection thermistor 5 correction thermistor 7 bridge circuit 8 correction circuit 9 diode 10 diode 11 resistor 12 series circuit Px first space Py second space S air passage Sx air passage End Sy Ventilation path other end H Air flow Sd Detection signal Pw Space part

Claims (5)

[Claims] 1. A differential pressure detecting device for detecting a differential pressure between a first space and a second space, wherein a ventilation path has one end facing the first space and the other end facing the second space. A housing that is inside, a detection thermistor that is arranged in the ventilation passage, and detects the airflow flowing in the ventilation passage due to the pressure difference between the first space and the second space, and detection based on the detection thermistor A differential pressure detecting device comprising a signal processing circuit for processing a signal. 2. A bridge thermistor including a correction thermistor and a detection thermistor is arranged in a space that is not affected by the air flow in the ventilation path, and a bridge circuit is formed. The differential pressure detection device described. 3. The differential pressure detection device according to claim 2, wherein the space portion is formed in the housing by branching from the air passage in a substantially right-angled direction. 4. The differential pressure detection device according to claim 2, wherein the signal processing circuit includes a correction circuit that is connected to the output side of the bridge circuit to correct the temperature characteristic of the bridge circuit. 5. The differential pressure detection device according to claim 4, wherein the correction circuit is composed of a series circuit of one or more diodes and a resistor.