Monitoring of the space rushing over

Introduction a new flow sensor from the house SCHMIDT Technology offers completely new characteristics. In a very slim metal housing hides itself a thermal flow probe, which can detect both the direction of flow and the flow rate in two directions can measure. This probe start, in order to improve within the range of the clean-room technology the flow monitoring clearly. One of the applications is the monitoring of the space rushing over. This report would like to point out, what hides itself behind the term space rushing over, with which means the space rushing over was so far determined and how the space rushing over can be improved with the help of this new sensor. Space rushing over, which is that? In pure areas if products are openly processed, then it must be frequently guaranteed that contaminated air from the neighbour areas does not penetrate into this area and thus the open products damages.One can guarantee that either by the fact that the areas are homogeneous closed (insulator technology) or thus that one guarantees an obligatory rushing over of air from the area which can be protected into the adjacent area. For this purpose in the area which can be protected an excess air pressure is developed and prevented due to its by each existing space opening air outward to flow and thus the penetration of contaminated air. For the maintenance of this stable situation it is usually sufficient to lead continuous supply air into the area provided with positive pressure and to regulate with the help of a differential pressure sensor the area on constant positive pressure. With positive pressure than 15 Pascal and with almost closely closed areas that is good larger to make. It acts however around an area, that over doors frequently which can be opened ordered or over large openings in the wall e.g..as product conveyors, then frequently such a large difference of pressure can not be regarded at all. At these areas logically with very small positive pressure it is worked and ensured product security by the fact that one supervises rushing over air between the areas in place of the differential pressure. Already if a suitable wall opening is present, then one can attach measuring instrument in this opening. Otherwise a special rushing over opening in the wall is attached. In order it evaluates to be able, how the space differential pressure affects the speed of rushing over, can in first approximation the "Torricelli' discharge law" be used if one considers that this view presupposes a thin wall and a hole of sufficient size.w=Wurzel from (2 x delta p/p) how: w = flow rate m/s delta p = differential pressure [ Pa ] p = density of the medium [ kg/m^3 ] under the conditions of a room air with 20°C with a standard air pressure of 1013,25 hPas results in the computation the following connection: Geschwindigkeitw [ m/s ] 0.01 0.13 0.1 0.41 1 1.29 5 2.89 10 4.08 15 5.00 20 5.77 30 7.07 on the basis this computation one can recognize Differenzdruck  [ Pa ] that a flow sensor attached in the rushing over opening can prove then still another rushing over, if only very small differential pressures are present. Past solutions the most reliable solution, in order to prevent back flows between areas is like already saying those to develop as high a differential pressure as possible. In pharmaceutical pure areas differential pressures between 15 and 30 Pascal are usual.That the adjusted differential pressure demanded rushing over produced is proven with the acceptance checkings by the visualization of the current by smoke particles. For the continuing monitoring of rushing over frequently differential pressure sensors are used, which prove that the necessary differential pressure will continuously maintain. The weak point of this solution is to be kept upright that the measuring signal of these sensors becomes instable with very small differential pressures and forces thus to it, a relatively high pressure. Alternatively in particularly brought in wall openings windfahnen are used, from which one can read off the direction of flow. Unfortunately this version is to be merged also relatively insensitive and because of the not existing electrical interface also not over the electronic Monitoringsystem. Alternatively partly also normal flow sensors are used, which are set up in the rushing over opening.Unfortunately these sensors cannot recognize, into which direction the current flows. The operational principle of the new sensor the flow sensor SS 20,400 is the first sensor from the house SCHMIDT its sensor element you direction of a flowing air to recognize can. This sensor works according to the principle of the thermal anemometer (also heat wire principle called). The thermal Anemometer unterscheiden itself by the following advantages of other air flow measurers: - minimum flow rates are measurably (starting from 0,05 m/s) - no moved parts and thus no wear - very small flow resistance b.z.w. small decrease of pressure at measuring point the new sensor of the type SS 20,400 has to exhibit still some further advantages, which are opened for us in the following one.Element and electronics in the mini format to the protection against mechanical load SCHMIDT built the sensor element into a chamber, was then called the whole to "chamber head". It was ensured by a careful aerodynamic organization of this chamber head that also a careless assembly of the sensor (easy rotating to the flow axle or dumps against the sensor axle) has a lowest possible reaction to the result of measurement. In the feeler pipe directly behind the sensor element super+small evaluation electronics, it sits looks thus in vain for an external transducer. A microprocessor, which is connected with the external world by the following connections, forms the core of electronics: Analogue output 4... 20 mA 0..10 V, direction exit, threshold value exit (both as open Collector) and R-S 232 interface. The analogue output supplies a linear output signal both with forward and to air with flowing backwards.Over the serial interface the user can adjust the sensor exactly to its needs. In addition offers SCHMIDT Technology a programming kit, which is to be served over a PC simply. The advantages of the new sensor · clear direction recognition · fairs into two directions · very fast responsing mode in the ms range · switching exits built therefore also as guards to the direct alarm giving applicable · very small dimensions · over PC parametrierbar · inserted contamination recognition · GMP suitable materials technical data design: Immersing probe (Ø 9 x 150 mm of inclusive. Stecker),   transducers in the feeler pipe integrates. Area of application: Freely flowing air and led air in pipes of 15 to 1,000 mm Messbereiche:  1/2.5/10/20 m/s (in both directions) measuring range beginning: 0.05 m/s pressure: atmospherically, 700..1300 hPa assembly: alternatively wandhalterung, flange or passage screw connection supply: 12... 24 VDC/under 10 mA of exits: possesses 0/4... 20 mA, 0..10 V, 0..5 V, 2 open Collector of exits for direction and threshold value R-S 232 to the Parametrierung the application of the new sensor of the SCHMIDT flow sensor SS 20,400 all characteristics, in order to be able to supervise rushing over mentioned before reliably. For the assembly of the sensor before the rushing over opening there is a suitable wall assembly flange. Into these the thin probe is screwed in and adjusted in such a way that the sensor element comes to lie in the center of the opening and that the feeler slot with the axle of the opening aligns. With the help of the analogue output the speed of air flowing by the rushing over opening can be supervised now.Since the sensor already measures starting from 0,05 m/s can a rushing over also is still proven if the differential pressure is already no longer clearly measurable. If the sensor can prove no more Vorwaertstroemung or if a back flow takes place, then it announces this condition over its switching exit OC1. With the help of the programming kit the user can absorb the analog signal of the sensor and stop the trigger levels of the switching exits themselves. Thereby can be ideally configured the sensor for each application. The new sensor is offered in different variants. Thus still further application possibilities within the range of the clean-room technology are opened for it: Laminar flow monitoring volume flow measurement in and exhaust air ducts cooling air monitoring flow control in inert gas atmospheres result the flow sensor SS 20,400 opens new possibilities for the flow monitoring in pure areas.Particularly for the monitoring of the space rushing over this sensor can book the following pluses: · stable measuring signal also with smallest differential pressures · avoidance of rash alarms · simple assembly · easy to clean in the inserted condition · fast installation and removal (e.g. for calibration) · calibration in each good wind tunnel possible references: Stoecker, paperback of physics, 2. Edition 1994