GB2128757A

GB2128757A - Measuring flow rate

Info

Publication number: GB2128757A
Application number: GB08327610A
Authority: GB
Inventors: Ken Orii; Takao Kawakami
Original assignee: Yamato Scientific Co Ltd
Current assignee: Yamato Scientific Co Ltd
Priority date: 1982-10-15
Filing date: 1983-10-14
Publication date: 1984-05-02
Also published as: DE3337398C2; DE3337398A1; GB2128757B; GB8327610D0

Abstract

Air is passed through a wire mesh (7) upstream of a flow sensor 9 to produce a more uniform velocity profile. The sensor is used to control the flow rate of filtered air supplied to a work station. <IMAGE>

Description

SPECIFICATION A clean bench The present invention relates to an outlet wind velocity measuring apparatus for a filter that is used in a clean bench.

Conventionally, it has been desirable for measurement of the wind velocity in a work space of the clean bench to carry out at the wind outlet side of filter.

However, if the filter has a complicated structure such as, for instance, a high capability one in which each filter element is offset to form a corrugated shape from air intake side to air outlet side, thereby providing a greater filtering area, there has been a problem that such a corrugated structure can cause the outlet wind velocity to vary at the air outlet side in the direction along the filter (that is, in the direction transversely crossing the air flow) and thus it is not possible to measure the wind velocity correctly.

Therefore, it has been suggested for measuring the wind velocity of the filter having the complicated structure as mentioned above to employ a method of detecting a volume of wind at the filter inlet side and of converting this value into the wind velocity, or in the case of measuring the wind velocity at the air outlet side, its measurement has been made at a position relatively remote from the filter's underside. The former method has a problem that greater fluctuations in the measurement values impair results of measurement, while the latter method is also problematic in that necessity of installting a measuring apparatus within the working space inevitably sacrifices the space available for the working operation.

An object of the present invention is to provide a Clean bench which has an outlet wind velocity measuring apparatus adapted to uniform the outlet wind velocity that is otherwise made variable by the structure of filter, thereby making it possible to correctly measure the outlet wind velocity at the filter's outlet side.

Another object of the present invention is to provide a Clean bench which has an outlet wind velocity measuring apparatus adapted to secure an ample space available for the working operation at the filter's air outlet side.

These and other objects and advantages of the present invention are accomplished by a provision of an outlet wind velocity measuring apparatus for a filter, wherein an air duct having a passage of suitable cross-sectional area adequate for the outlet wind flowing from the filter to pass is vertically secured to the filter's outlet side, the outlet side being formed in a corrugated shape by offsetting filter elements from air intake side to air outlet side, the passage of the air duct is provided with a flow rectifier adapted to rectify the flow of outlet wind passing through the passage, and the rectifier is provided at its air outlet side thereof a wind velocity sensor adapted to detect the outlet wind velocity rectified by the rectifier.

These and other objects, features and advantages of the present invention will become more apparent upon a reading of the following detailed description and drawings in which: Figure 1 is an elevational view and side view of a clean bench equipped with the measuring apparatus constructed in accordance with the present invention; Figures 2, 3 and 4 are respectively an elevational view, a side view and a rear elevation of the outlet wind velocity measuring apparatus.

With reference to Fig. 1, the clean bench is constructed such that it can feed a clean air vertically to the working space 11. That is, the clean bench is constructed in such way that it can draw an air via a prefilter 1 5 from an air inlet port 1 3 defined at the lower side thereof, and after a through removal of dirts, vertically feed the clean and asceptic air to the working space with a subsequent discharge thereof out of the front. For its corrugated structure of offsetting filter elements from air inlet side to air outlet side, the filter 1 ensures greater filtering area.

The filter 1 is provided at the air inlet side thereof with an outlet wind measuring apparatus adapted to measure the velocity of outlet wind flown from the filter 1. As shown in Figs. 2, 3 and 4, the outlet wind velocity measuring apparatus 1 9 has the air duct 5 including the passage of suitable cross-sectional area (squarely shaped in the embodiment shown) vertically secured to the outlet side of the filter 1 in a close relationship with the filter 1, and being supported by a machine frame 23 via a support frame 21.

Tensionably horizontally mounted with the passage of the air duct 5 is a rectifier 7 adapted to rectify the flow of air passing through the passage. The rectifier 7 is made of, as for example, a stainless steel wire gauze having outside diameter of 0.5 mm and pitch size of 1.8 mm.

The rectifier 7 is provided at the lower portion thereof a wind velocity sensor 9 such as a hotwire anemometer and the like capable of detecting the outlet wind velocity rectified by the rectifier 7. The wind velocity sensor 9 is supported by a support bracket 25 provided at the side wall 5' of the air duct 5 and is interposed into the passage.

Though not shown in Figures, a controlling means is provided to connect the wind velocity measuring apparatus to the air blower. The controlling means function to compare the wind velocity detected by the wind velocity sensor 9 with the predetermined wind velocity, and if there is any discrepancy between the two values, it further controls the air blower automatically for increasing or slowing down its r.p.m. Furthermore, the controlling means is adapted to produce an alarm upon a minimum wind velocity being detected.

There are further arranged a shutter 27, a fluorescent lamp 29 respectively provided at the front and upper portions of the working space 11, and a light diffuser 31.

Several functions attainable by the present invention will be described hereinbelow.

The air drawn via the prefilter 1 5 from the air inlet port 1 3 provided at the lower portion of the clean air bench is blown by the air blower 1 7 to pass through the filter 1 to the air outlet side. Despite a tendency for the outlet wind velocity to vary and fluctuate under the influence of filter's structure, use of the air duct 5 can serve to uniform the fluctuating wind velocity by the rectifier 7 which functions to rectify the air flow while in passing through the passage in the air duct. The wind velocity sensor 9 detects the velocity of outlet wind thus uniformed, thereby making it possible to correctly measure the outlet wind velocity at the air outlet side of filter 1.

Measurement results of the outlet wind velocity taken at a fixed point of the secondary side of the HEPA filter, used as a filter 1 are given below, comparing the results of the case where the wind velocity sensor 9 is installed directly with those of the case where the wind velocity sensor 9 is installed via the outlet wind velocity measuring apparatus constructed in accordance with the present invention.

Installing Condition of Variance at Laternal Longitudinal Wind Velocity sensor Fixed Point Fluctuation Fluctuation Without wind velocity measuring + 0.01 apparatus 0.57 (m/s) 0.07 (m/s) 0.10 (m/s) With wind velocity measuring apparatus i 0.005 installed (as embodyed) 0.36 (m/s) 0.02 (m/s) 0.01 (m/s) As apparent from the above table, variance in the outlet wind velocity by positions can be uniformed to 1/3.5 to 1/10 times less in the case where the wind velocity sensor 9 is installed via the outlet wind velocity measuring apparatus 19, compared to the case where the wind velocity sensor is installed directly.

In addition, the clean bench with the wind velocity measuring apparatus secured to the understream of the filter, and is equipped with the controlling means adapted to control the r.p.m. of the air blower in response to the wind velocity detected by the wind velocity sensor 3, can afford the effects as undermentioned.

a. By providing the wind velocity sensor upwardly of the working space at the understream of the filter, the wind velocity at the working space can be directly detected, making it possible to correctly detect the air current condition.

b. A provision of a controlling means adapted to control the r.p.m. of the air blower by comparing the wind velocity detected with the predetermined value can permit the wind velocity at the working space to be kept at constant as predetermined, thereby realizing a stable air current condition.

c. In the case that the operation is carried out with the shutter slightly opened, the filter can extend its working life by predeterming the wind velocity lower than usual beforehand.

Meanwhile, the present invention is not limited its application merely to the embodiment mentioned as above, but the air duct, as for example, may be constructed with its crosssectional area as circular.

As apparent from the foregoing description, the construction in accordance with the present invention can serve to uniform the outlet wind velocity that may otherwise be functuated at the air outlet side of the filter wherein filter elements are offset to form a corrugated shape from air intake side to air outlet side. Therefore, it becomes possible for the wind velocity sensor to be mounted closely to the filter, and to obtain a correct wind velocity simultaneously. As a result, the working space to be formed at the air outlet side of the filter can be made ample.

Claims

1. An outlet wind velocity mesuring apparatus for the filter provided in a clean bench, comprising an air duct vertically arranged at the air outlet side of said filter, a rectifier means provided at the passage of said air duct, and a wind velocity sensor provided at the air outlet side of said rectifier means, said wind velocity sensor adapted to detect the velocity of the outlet wind rectified by said rectifier means.

2. An outlet wind velocity mesuring apparatus wherein, said rectifier means is a steel wire gauze.

3. A wind velocity controlling apparatus for a clean bench, comprising a wind velocity sensor provided in the downstream of the filter at the upward position of the working space, and a controlling means for controlling the r.p.m. of the air blower in response to the wind velocity detected by said wind velocity sensor so that the wind velocity at the downstream of the filter can be maintained at a predetermined value.

4. Apparatus for measuring the wind velocity downstream of a filter in a clean bench, which apparatus comprises means for rectifying the air flow downstream of the filter and means for measuring the wind velocity downstream of the rectifying means.

5. Apparatus for controlling the wind velocity in a clean bench, which apparatus comprises means for sensing the wind velocity downstream of a filter of the clean bench and means responsive to the sensing means for controlling the wind velocity so as to maintain the same at a predetermined value.

6. Measuring apparatus, substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

7. Controlling apparatus, substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

8. Any novel feature or combination of features described herein.