Flow sensor and gas detector

Abstract

To provide a flow sensor capable of detecting a gas backflow and performing flow detection high in reliability without accompanying with increase in the number of components and enlargement in size, and a gas detector capable of performing gas detection high in reliability.SOLUTION: A flow sensor 110 for detecting a gas flow rate on the basis of the level of change in temperature formed by reducing the temperature of a resistance heating element heated by energization by a gas flow includes a compensation chamber 125 arranging a compensation element 135 divided from a gas passage 115 by a partition 120. In the partition 120, an opening 121 spatially connecting the compensation chamber 125 with the gas passage 115 is formed at a position of entering gas flowing toward a gas introduction part 112 side from a gas discharge part 113 side into the compensation chamber 125 without directly entering the gas flowing toward the gas discharge part 113 side from the gas introduction part 112 side. A gas detector 100 includes the flow sensor 110.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a flow sensor that detects a gas flow rate based on the degree of temperature change in which the temperature of a resistance heating element heated by energization is decreased by a gas flow, and a gas detector including the flow sensor. Based on the degree of the temperature change in which the temperature of a resistance heating element heated by energization is decreased by a gas flow, and a gas detector including the flow sensor.

Background Art

[0002] For example, in a suction-type gas detector, it is necessary to stably supply a gas sensor with a proper flow rate according to the type of the gas to be detected or the characteristics of the gas sensor, etc., and the gas flow rate is monitored using an appropriate flow sensor. As the suction means, for example, a diaphragm pump or the like is used.

[0003] As the flow sensor, for example, a thermal flow sensor that measures the flow rate based on the magnitude of the energization amount supplied to a resistance heating element that is cooled by a gas flow and whose temperature decreases is used (see, for example, Patent Document 1). In such a flow sensor, a bridge circuit is constituted by two elements, a flow detection element arranged on a gas flow path and a compensation element arranged at an isolation position where gas substitution is performed only by gas diffusion and not cooled by the gas flow, and the change in the resistance value due to the temperature change of the flow detection element is detected as a voltage, and the gas flow rate can be obtained.

[0004] However, the gas flow supplied by a diaphragm pump is a so-called pulsating flow accompanied by pulsation, and the flow rate of the supplied gas is not constant and causes flow rate fluctuations. Further, not limited to the pulsating flow (gas flow including a reverse flow component) by a diaphragm pump, for example, when a problem such as clogging of a gas flow path occurs, a reverse flow may occur. In the above flow sensor, since a temperature change occurs if there is a gas flow, there is a problem that the direction of the gas flow cannot be distinguished and accurate flow rate measurement cannot be performed. Therefore, in flow measurement, it is required to reduce the pulsation of the gas flow and supply a stable-flow gas to the flow detection element, and to detect the direction of the gas flow to detect the flow rate, etc.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Although various flow path structures for reducing the pulsation of the gas flow have been proposed, they do not prevent the occurrence of reverse flow of the gas flow itself, and the fact is that they cannot sufficiently suppress the decrease in detection accuracy due to the reverse flow of the gas flow. Further, as a method for preventing the reverse flow of the gas flow, for example, providing a check valve separately is also conceivable, but there is a problem that the structure becomes complicated and large-sized due to an increase in the number of parts. Further, as a method for detecting the reverse flow of the gas flow, for example, providing a separate element for detecting the reverse flow of the gas flow or correcting the output change due to the reverse flow of the gas flow by output processing is conceivable. However, there are problems such as complication of the control circuit and complication and enlargement of the structure of the sensor.

[0007] The present invention has been completed in view of such circumstances, and an object of the present invention is to provide a flow rate sensor capable of detecting the reverse flow of a gas flow and performing highly reliable flow rate detection without increasing the number of parts and without enlargement. Another object of the present invention is to provide a gas detector capable of performing highly reliable gas detection.

Means for Solving the Problems

[0008] The flow rate sensor of the present invention is a flow rate sensor that detects the gas flow rate based on the degree of temperature change in which the temperature of a resistance heating element heated by energization is decreased by the gas flow. The flow rate sensor includes a sensor body having a gas introduction portion and a gas discharge portion. Inside the sensor body, a gas flow path extending from the gas introduction portion to the gas discharge portion and a compensation chamber formed by being partitioned from the gas flow path by a partition wall are formed. A flow rate detection element composed of a resistance heating element is disposed on the gas flow path, and a compensation element composed of a resistance heating element is disposed in the compensation chamber. The partition wall has an opening that spatially connects the compensation chamber to the gas flow path. By forming the opening at a position where the gas flowing from the gas introduction portion side toward the gas discharge portion does not directly flow into the compensation chamber and at a position where the gas flowing from the gas discharge portion side toward the gas introduction portion side can flow into the compensation chamber, the above problems are solved.

[0009] The gas detector of the present invention is a gas detector including a gas sensor disposed in a gas flow path, a diaphragm pump that supplies a gas to be detected to the gas sensor through the gas flow path, and a flow rate sensor that detects the flow rate of the gas flowing through the gas flow path. By using the above flow rate sensor as the flow rate sensor, the above problems are solved.

Effects of the Invention

[0010] According to the invention according to claim 1, during the normal flow in which the gas flow is from the gas introduction portion side toward the gas discharge portion side, since the gas flow does not hit the compensation element, it is possible to compensate for the output change due to the heat conduction of the gas (including humidity) and the environmental temperature. During the reverse flow in which the gas flow is from the gas discharge portion side toward the gas introduction portion side, since the gas flow flows into the compensation chamber through the opening and hits the compensation element, it is possible to detect the reverse flow of the gas. Therefore, by preventing the detection of the output change due to the reverse flow, it is possible to accurately detect the gas flow rate. Moreover, since the reverse flow of the gas flow can be detected by the flow path structure of the gas flow path, there is no need to separately use other components such as detection elements for reverse flow detection other than the compensation element, and the control circuit does not become complicated. Therefore, it is possible to avoid complication and enlargement of the structure of the sensor itself.

[0011] According to the invention according to claim 2, when the gas flow reverses and flows from the gas discharge part side toward the gas introduction part side, the gas flow can be surely made to flow into the compensation chamber and detected by the compensation element. According to the invention according to claim 3, when the gas flow is in the forward flow flowing from the gas introduction part side toward the gas discharge part side, the influence on the compensation element of the gas flow flowing through the main flow path can be suppressed or eliminated, and when the gas flow flows from the gas discharge part side toward the gas introduction part side, the gas flow can be surely applied to the compensation element. According to the invention according to claim 4, the degree of freedom in design regarding the flow path structure is increased, and for example, even when gas is introduced by a diaphragm pump, the pulsation of the gas flow flowing through the gas flow path can be reduced, and the flow rate detection can be stably performed.

[0012] According to the invention according to claim 5, since the gas flow rate can be detected with high accuracy by the flow rate sensor, a test gas with an appropriate flow rate can be supplied to the gas sensor, and highly reliable gas detection can be performed.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4A

Figure 4B

Embodiment for Carrying Out the Invention

[0014] The flow rate sensor of the present invention is a thermal flow rate sensor that detects the gas flow rate based on the degree of temperature change in which the temperature of a resistance heating element heated by energization decreases due to the gas flow. As shown in FIG. 1, for example, in a gas detector 100 in which the gas to be inspected is introduced by a suction means 106 such as a diaphragm pump with respect to a gas flow path 101 where a gas sensor 105 is arranged, it is used for detecting the flow rate of the gas to be inspected flowing through the gas flow path 101. The flow rate sensor 110 is arranged, for example, at a position downstream of the gas sensor 105 in the gas flow direction.

[0015] As shown in FIG. 2, the flow rate sensor 110 according to the present embodiment includes a sensor main body 111 in which a gas flow path 115 extending from a gas introduction part 112 to a gas discharge part 113 is provided inside. The gas introduction part 112 and the gas discharge part 113 are formed such that the gas inlet 112a and the gas outlet 113a open in the same direction.

[0016] In the present embodiment, the gas flow path 115 has a main flow path 116 formed in a bent shape by bending at a plurality of locations, and a bypass flow path 117 that connects two flow path portions extending in the same direction in the main flow path 116. By forming the main flow path 116 in a bent shape, for example, even when gas is introduced by a diaphragm pump, the pulsation of the flowing gas flow can be reduced, and it becomes possible to stably perform flow rate detection. The flow path diameter of the bypass flow path 117 is formed smaller than the flow path diameter of the main flow path 116, and a flow rate detection element 130 is arranged in the bypass flow path 117. By configuring the flow path diameter of the bypass flow path 117 where the flow rate detection element 130 is arranged to be smaller than the flow path diameter of the main flow path 116, the pulsation reduction effect of the gas flow can be obtained, and it becomes possible to supply the flow rate detection element 130 with gas having a stable flow rate.

[0017] The flow rate detection element 130 is constituted by, for example, a resistance heating element in which a metal wire made of platinum or an alloy thereof is wound in a coil shape, and is arranged in a posture in which the coil winding axis direction extends in a direction orthogonal to the gas flow. Here, as the metal wire, it is preferable to use one that has been subjected to a non-reactive treatment such as vapor deposition coating of gold in order to suppress reactions such as combustion with respect to the gas to be detected.

[0018] This flow rate sensor 110 includes a compensation chamber 125 partitioned from the main flow path 116 by a partition wall 120. An opening 121 that spatially connects the compensation chamber 125 to the main flow path 116 is formed in the partition wall 120. The opening 121 is located at a position where the gas to be detected does not directly flow into the compensation chamber 125 during normal flow when the gas to be detected flows from the gas introduction part 112 side toward the gas discharge part 113 side, and is formed at a position where the gas to be detected can flow into the compensation chamber 125 during reverse flow when the gas to be detected flows from the gas discharge part 113 side toward the gas introduction part 112 side. In the present embodiment, the opening 121 is formed to open in the same direction as the opening direction of the gas outlet 113a at a position facing the gas outlet 113a. Thereby, during reverse flow when the gas flow flows from the gas discharge part 113 side toward the gas introduction part 112 side, the gas flow can be reliably made to flow into the compensation chamber 125 and detected by the compensation element 135.

[0019] The compensation element 135 has the same configuration as the flow rate detection element 130 and is constituted by, for example, a resistance heating element in which a metal wire made of platinum or an alloy thereof is wound in a coil shape. Here, as the metal wire, it is preferable to use one that has been subjected to a non-reactive treatment such as vapor deposition coating of gold in order to suppress reactions such as combustion with respect to the gas to be detected. The compensating element 135 is arranged in a posture where the coil winding axis direction extends along the opening direction of the opening 121 of the partition wall 120 in the compensation chamber 125 at a position not facing the opening 121. Thereby, when the gas flow is in the forward flow from the gas introduction part 112 side toward the gas discharge part 113 side, it is possible to suppress or eliminate the influence of the gas flow passing through the gas flow path 115 on the compensating element 135.

[0020] In the compensation chamber 125, an air guiding part 126 for directing the gas flowing into the compensation chamber 125 toward the compensating element 135 is provided. In the present embodiment, the air guiding part 126 is constituted by a wall that extends obliquely with respect to the opening direction of the opening 121, and the gas flowing into the compensation chamber 125 hits the compensating element 135 from the inclined direction with respect to the coil winding axis. Thereby, it is possible to reliably detect the reverse flow of the gas flow.

[0021] In this flow rate sensor 110, as shown in FIG. 3, a bridge circuit 140 is constituted by the flow rate detection element 130, the compensating element 135, and the resistance element 141. By supplying a constant current to the flow rate detection element 130 and the compensating element 135 by the constant current power supply 142 so that the flow rate detection element 130 and the compensating element 135 are in a state of being heated to a predetermined temperature, the change amount of the resistance value of the flow rate detection element 130 generated when the gas to be detected contacts the flow rate detection element 130 is taken out as a voltage value by the voltmeter 143. The gas flow rate is detected based on the calibration curve data showing the relationship between the output voltage and the gas flow rate.

[0022] As shown in FIG. 4A, when the gas to be detected is in the forward flow (the gas flow is indicated by a white arrow in FIG. 4A) flowing from the gas introduction part 112 side to the gas discharge part 113 side in the gas flow path 115, the gas to be detected flows into the compensation chamber 125 only by gas diffusion. For this reason, the compensating element 135 does not directly receive the gas flow, and no temperature change of the compensating element 135 occurs. On the other hand, as shown in FIG. 4B, during reverse flow in which the gas to be detected flows from the gas discharge section 113 side to the gas introduction section 112 side in the gas flow path 115 (indicated by the arrow that fills the gas flow in FIG. 4B), the gas to be detected flows into the compensation chamber 125 through the opening 121, so that the compensation element 135 directly receives the gas flow. As a result, since the temperature of the compensation element 135 decreases and the resistance value changes, it is possible to distinguish whether the gas flow of the gas to be detected flowing through the gas flow path 115 is a forward flow or a reverse flow.

[0023] Thus, according to the flow rate sensor 110 having the above configuration, it is possible to accurately detect the gas flow rate by preventing the detection of an output change due to reverse flow. Moreover, since it is possible to detect the reverse flow of the gas flow due to the flow path structure of the gas flow path 115, there is no need to separately use other components such as a detection element for reverse flow detection other than the compensation element 135, and the control circuit does not become complicated. Therefore, it is possible to avoid the complication and enlargement of the structure of the sensor itself.

[0024] As described above, the embodiments of the present invention have been described. However, the present invention is not limited to the above embodiments, and various modifications can be made. For example, in the above embodiment, the configuration in which the compensation chamber is formed at a position on the gas discharge section side with respect to the flow rate detection element has been described. However, the compensation chamber may be formed at a position on the gas introduction section side with respect to the flow rate detection element. In addition, the configuration in which the opening that spatially connects the compensation chamber and the main flow path is formed at a position facing the gas outlet has been described. However, as long as it is formed at a position where the gas to be detected can flow into the compensation chamber during reverse flow, the formation position of the opening is not particularly limited. In addition, although the configuration in which the main flow path is formed in a bent shape has been described, the main flow path may have a flow path structure that reduces pulsation, for example, by forming a buffer (buffer section). Furthermore, the suction means is not limited to a diaphragm pump.

Description of Reference Numerals

[0025] 100 ··· Gas detector 101 ··· Gas flow path 105 ··· Gas sensor 106 ··· Suction means 110 ··· Flow rate sensor 111 ··· Sensor body 112 ··· Gas introduction part 112a ··· Gas inlet 113 ··· Gas discharge part 113a ··· Gas outlet 115 ··· Gas flow path 116 ··· Main flow path 117 ··· Bypass flow path 120 ··· Partition wall 121 ··· Opening 125 ··· Compensation chamber 126 ··· Air guide part 130 ··· Flow rate detection element 135 ··· Compensation element 140 ··· Bridge circuit 141 ··· Resistance element 142 ··· Constant current power supply 143 ··· Voltmeter

Claims

1. A flow rate sensor that detects a gas flow rate based on the degree of temperature change in which the temperature of a resistance heating element heated by energization is decreased by a gas flow, comprising a sensor body having a gas introduction part and a gas discharge part, inside the sensor body, a gas flow path extending from the gas introduction part to the gas discharge part and a compensation chamber partitioned from the gas flow path by a partition wall are formed, a flow rate detection element constituted by a resistance heating element is disposed on the gas flow path, and a compensation element constituted by a resistance heating element is disposed in the compensation chamber, the partition wall has an opening that spatially connects the compensation chamber to the gas flow path, the opening is formed at a position where gas flowing from the gas introduction part side toward the gas discharge part does not directly flow into the compensation chamber, and at a position where gas flowing from the gas discharge part side toward the gas introduction part side can flow into the compensation chamber. The flow rate sensor is characterized by this.

2. The flow rate sensor according to claim 1, wherein the opening is formed at a position facing the gas discharge part.

3. The compensation element is constituted by a metal wire that generates heat by energization being wound in a coil shape, and the coil winding axis is disposed in a posture extending along the opening direction of the opening, The flow rate sensor according to claim 1, wherein a wind guiding part for guiding the gas flowing in from the opening to the compensation element is provided in the compensation chamber.

4. The gas introduction part and the gas discharge part are formed such that the gas inlet and the gas outlet open in the same direction as each other, The flow rate sensor according to claim 1, wherein the gas flow path is formed in a bent shape bent at a plurality of locations.

5. A gas detector comprising a gas sensor disposed in a gas flow path, a diaphragm pump for supplying a gas to be detected to the gas sensor through the gas flow path, and a flow rate sensor for detecting the gas flow rate flowing through the gas flow path, The gas detector is characterized in that the flow rate sensor is the flow rate sensor according to any one of claims 1 to 4.

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