JPH0658316B2 - Flow control device for sample air in particle detector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a sample air flow rate control device in a particle detection device for detecting particles such as dust and smoke in the air.

(Prior art) Sample air taken in from the outside is made to flow into the detection site in the dark box, and the scattered light when it hits the fine particles in the sample air from the light source is detected by the light receiving element, and the unit amount of sample air is detected. There is a particle detection device that counts the number of particles inside.

In this type of detection device, a constant amount of sample air needs to be constantly flown to the detection site in a unit time, so a pump is conventionally used and a method of controlling the rotation speed of the pump is adopted.

(Problems to be Solved by the Invention) However, since the pump has a movable part, it is large in size, high in cost, and likely to break down. Therefore, regular maintenance is required and management is complicated. there were.

In view of such conventional problems, the present invention utilizes a heater having no movable parts to flow sample air to a detection site and control the flow rate of the sample air.

(Means for Solving the Problem) In the present invention, the light from the light source 19 is condensed on the detection site 6 in the dark box 4, and the scattered light from the fine particles in the sample air flowing through the detection site 6 is received by the light receiving element 24. In the particle detection device for detection, heaters 11 and 12 are provided on the air intake 7 side and the air discharge port 8 side of the dark box 4 to heat the sample air and generate convection. Temperature sensor 17 whose detected temperature changes depending on the flow rate of sample air due to convection generated by heating of 12 and the detected temperature from this temperature sensor 17 are compared with the set value so that the detected temperature and the set value become equal. The control means 39 for controlling the amount of heat generated by the heaters 11 and 12 is provided.

(Operation) When the heaters 11 and 12 generate heat, the sample air is heated to generate convection, which flows through the detection site 6.

Since the detected temperature of the temperature sensor 17 changes depending on the flow rate of the sample air, the control means 39 compares the detected temperature with a set value and controls the heat generation amounts of the heaters 11 and 12 so that the detected temperature and the set value become equal. . As a result, the flow rate of the sample air flowing through the detection site 6 can be controlled.

(Example) Hereinafter, the present invention will be described in detail with reference to the illustrated example.
In FIG. 3 and FIG. 3, 1 is the case of the detection device,
Inside the case 1, a mounting plate 2 and a circuit board 3 are provided. 4 is a dark box attached to the mounting plate 2, and the interior space is a dark room 5. In order to allow the sample air to flow from the lower side to the upper side of the detection site 6 in the dark chamber 4, the air intake 7 at the lower part and the air discharge port at the upper part correspond to the upper and lower parts of the detection site 6. Each exit 8 is formed. And the air intake duct 9 is installed in the air intake port 7
Air discharge ducts 10 are connected to 8 respectively. Each of the ducts 9 and 10 has a rectangular tube shape in cross section, and is formed into a hook shape bent at four bent portions so that it is difficult for external light to enter the dark room 5, and the left and right along the mounting plate 2. It is formed long in the direction. Further, heaters 11 and 12 are provided at the inlet sides of the air intake duct 9 and the air discharge duct 10 so that the sample air flows by convection. Heater 11,12
Is composed of a resistor, and the lead pins 15 and 16 at both ends are fixed to the mounting plate 2 in a state where the main bodies 13 and 14 are along the air flow direction in the ducts 9 and 10. Reference numeral 17 is a temperature sensor composed of a thermistor or the like, and is fixed to the mounting plate 2 by a lead pin 18 so as to be located on the inlet side of the air intake duct 9 so that the detected temperature changes depending on the flow rate of the sample air.

A light source 19 such as an infrared light emitting diode is mounted on the mounting plate 2 via a light source case 20. Reference numeral 21 denotes a condenser lens, which is attached to the tip of the light source case 20 so as to be positioned at the opening of the dark box 4. The condenser lens 21 has a focal length such that the light from the light source 19 is condensed at the detection site 6. Are used.

Reference numeral 22 denotes a light-sealing device, which is configured to absorb the light from the light source 19 and prevent the light from leaking into the dark room 5, and is arranged on the optical axis 23 facing the light source 19.

24 is a light receiving element such as a phototransistor, which is housed in a light receiving case 25 mounted on the mounting plate 2 with an inclination of about 35 ° with respect to the optical axis 17, and at the tip of the light receiving case 25, The condenser lens 26 is attached so that 6 is the focal point. Therefore, the light receiving element 24 can detect the scattered light through the condenser lens 26 if the sample air flowing through the detection site 6 contains fine particles. The case 1 is provided with ventilation holes 27 and 28 corresponding to the ducts 9 and 10, respectively.

The light receiving element 24 is connected to a waveform shaper 30 via an amplifier 29, as shown in FIG. The waveform shaper 30 has an amplifier 29.
The output signal [(A) in FIG. 4] is shaped into a pulse signal [(B) in FIG. 4] with reference to a predetermined level. 31 is a central processing unit of a microcomputer, which reads and counts pulse signals from the waveform shaper 30, and performs absolute evaluation or relative evaluation based on the count value, and outputs them to the display unit 32 and the control output unit 33, respectively. It is designed to output. Absolute evaluation is to judge the number of particles in the sample air with reference to the time when the number of particles in the air is zero. The number of fine particles increased or decreased is determined, and the bead switching is performed by the operation unit 34. The central processing unit 31 is connected to the host computer 35 and is centrally managed by the host computer 35.

36 is a comparator, which is the temperature detected by the temperature sensor 17 and the setting device 37.
Of the current controller 38
Is configured to drive. The current controller 38 controls the amount of heat generated by adjusting the current flowing through the heaters 11 and 12. Then, these comparator 36 and current controller 38
The control means 39 is constituted by and the heater so that the temperature detected by the temperature sensor 17 and the set value become equal.
Controls the heating value of 11, 12. An A / D converter 40 A / D converts the deviation signal of the comparator 36 and feeds it back to the central processing unit 31.

In the above structure, the light output from the light source 19 in the direction of the optical axis 23 is condensed by the condensing lens 21, and the detection site 6 in the dark box 4 is
Concentrate on. On the other hand, when the heaters 11 and 12 are energized to generate heat, the air is heated by this, and convection occurs, and as shown in FIG. 2, external air is used as sample air from the air intake duct 9 to the dark box. 4 taken in,
The sample air in the dark box 4 is discharged to the outside through the air discharge duct 10. For this reason, the sample air flows upward from the air intake port 7 to the air discharge port 8 at the detection site 6, so if there are fine particles in the sample air, the light from the light source 19 will hit the fine particles and scatter. The scattered light is condensed and incident on the light receiving element 24 via the condenser lens 26.

When the light receiving element 24 receives the scattered light, the level of the output signal rises when receiving the light and changes as shown in FIG. 4 (A). Then, after amplifying this output signal by the amplifier 29, the waveform is shaped by the waveform shaper 30 into a pulse signal as shown in FIG. 4 (B), and is input to the central processing unit 31 to count the number of pulses, that is, the number of fine particles. , Performs predetermined arithmetic processing. Then, the calculation result is displayed on the display unit 32 and the control output unit 33 outputs the control output.

Since the number of fine particles is in a unit amount of sample air, it is necessary to always flow a constant flow of sample air to the detection site 6. Therefore, when the temperature of the sample air is substantially constant, the temperature detected by the temperature sensor 17 changes depending on the flow rate of the sample air, and thus the temperature sensor 17 indirectly detects the flow rate of the sample air. Then, the temperature detected by the temperature sensor 17 is compared with the set value of the setter 37 by the comparator 36, and the current controller 38 is driven by the deviation signal. Then the current controller
Since 38 controls the current flowing through the heaters 11 and 12 and controls the heat generation amount of the heaters 11 and 12 so that the detected temperature becomes equal to the set value, a constant sample air always flows through the detection portion 6. For example, if the flow rate of the sample air is low and the temperature detected by the temperature sensor 17 rises, the comparator 36, the current controller 38
The current of the heaters 11 and 12 is increased via the to increase the amount of heat generation. Then, since the sample air is heated, the flow rate of the sample air increases and is constantly controlled to be a constant flow rate.

The setter 37 is a variable type, and the set value can be changed according to the purpose, and the flow rate of the sample air can be arbitrarily controlled by changing the set value. A fixed type may also be used.

(Effects of the Invention) According to the present invention, the sample air is heated by using the heaters 11 and 12 to generate convection to flow the sample air, so that it is smaller and cheaper than the conventional pump type. It can be carried out and maintenance free. Moreover, the flow rate of the sample air is detected by the temperature sensor 17 as a change in temperature, and this is compared with the set value so that the two become equal to each other.
Since the configuration in which the heat generation amount of the heaters 11 and 12 is controlled by 39 is adopted, the flow rate of the sample air can be controlled even though the heaters 11 and 12 are used.

[Brief description of drawings]

The drawings show one embodiment of the present invention. FIG. 1 is an overall configuration diagram, FIG. 2 is a sectional front view of a detector, FIG. 3 is a sectional bottom view thereof, and FIGS. It is a waveform diagram. 4 …… Dark box, 6 …… Detection area, 9 …… Air intake duct,
10 …… Air discharge duct, 11, 12 …… Heater, 17 …… Temperature sensor, 19 …… Light source, 21, 26 …… Condensing lens, 24 ……
Light receiving element, 36 …… Comparator, 37 …… Set value, 39 …… Control means.

Claims (1)

[Claims] 1. The light from the light source (19) is focused on the detection site (6) in the dark box (4), and the scattered light from the fine particles in the sample air flowing through the detection site (6) is received by the light receiving element (24). ) In the particulate detection device, the dark box (4), the air intake (7) side and the air discharge (8) side,
Heater to heat the sample air and generate convection
(11) (12) is provided, the temperature sensor (17) whose detection temperature changes depending on the flow rate of the sample air due to convection generated by heating the heaters (11) and (12), and the detection from this temperature sensor (17) A particle detection device comprising a control means (39) for comparing the temperature with a set value and controlling the heat generation amount of the heaters (11), (12) so that the detected temperature and the set value are equal. Flow control device for sample air.