Differential Pressure in Cleanrooms

Accurate environmental monitoring systems and methods are essential for critical process rooms (cleanrooms) and mini environments (MEs) to maintain consistent operation within specifications. The quality of your products, whether pharmaceutical medicines, semiconductor chips, or manufacturing processes, is more important than simply meeting standards. Regarding pressure measurement, Ziebaq has you covered with their robust and extremely accurate differential pressure instruments. These instruments will keep your cleanroom running smoothly.

It is possible to bring up several standards while discussing cleanrooms. Various standards outline specific requirements for differential pressure differences; for example, VDI 2083 (3), DIN EN ISO 14644-3/4 cleanroom classification, GMP Annex 1 of 5-20 or 5-15 Pa, and VDI 2083-19, which deals with the tightness of containments.

Creating pressure cascades between rooms is the principal method for protecting people, products, and the manufacturing environment. The goal is to keep the air flowing from the clean room to the uncontrolled room. Additional methods employed for cleanroom maintenance include point-and-surface-air extraction, clean-air hoods, laminar flow workspaces, air curtains, filter fan units, mini environments, Restricted Access Barrier Systems (RABS), safety workbenches for biology or related fields, glove boxes, clean machines, isolators, and other compartments.

You Can Read Also: Principles Of Cleanroom Validation

Differential Pressure: What Is It?

Opening the door to a cleanroom allows contaminants to seep in, resulting in a pressure drop. On the other hand, an excessively high level of pressure inside a cleanroom result in energy loss. Controlling the cleanroom's temperature, humidity, airflow, and pressure is essential. For example, when the other two parameters are well-balanced, cleanrooms work as intended, but pressure is the most important and crucial of these three.

For example, if two points, A and B, have 200 psi and 100 psi, respectively, the differential pressure would be 100 psi (200 psi - 100 psi). In cleanrooms, factories, and HVAC (Heating, Ventilation, and Air-conditioning) labs, even small pressure variations can have a major impact, making differential pressure a crucial factor. Differential pressure in a cleanroom prevents dirt and debris from settling into more pristine spots.

The measurement of airflow velocity and pressure allows for improving and monitoring cleanroom operational safety. Differential pressure control and airflow tracking are essential for pressurization control. Pressurization control is essential to confirm and maintain the cleanroom parameters. The positive pressurization of the surrounding areas is necessary for cleanrooms to establish buffer zones and minimize the risk of unintentional contamination.

Specifications for cleanroom measurements

The lowest allowable differential pressure measurement range is zero to fifty pascals (Pa), as per DIN EN ISO 14644-3. Instruments designed for use in cleanrooms must have minimal measurement uncertainty to accomplish this measurement accurately. To measure extremely minute pressure differences unaffected by the typical long-term drift caused by ageing or mounting positions, Ziebaq offers a particular product line that incorporates an automatic mechanical zero point.

Instruments sold into cleanrooms typically have a bi-directional range, such as -25 to +25Pa, to guarantee proper airflow by maintaining an overpressure. It is possible to prove for crucial productions that the room pressure did not fall below 0 Pa differential pressure between contamination classes using this measurement range. It is crucial in these instances to have the mechanical auto-zero's low uncertainty.

Techniques for measuring in cleanrooms

In cleanrooms, two primary ways of measuring differential pressure are in use. The so-called "static"-method and the "dynamic" differential pressure method are based on the principle of thermal mass flow. Attached to two temperature-sensitive resistors is a heating element that forms the basis of this measuring technology. An elevated temperature profile on one of the resistors happens when airflow happens, depending on the direction of the flow. 

The principle of static measurement is based on the strain gauge technique. The basic idea is to use a piezo-resistive MEMS sensor to measure the force applied when a diaphragm is stretched rather than the pressure applied directly to the sensor. Technology has progressed, and both approaches have advantages and disadvantages. Ziebaq has been making sensors for a long time, so they're familiar with both approaches.

Controlled environment in cleanrooms

Currently, a high-accuracy piezo-resistive element is the standard component for static detection methods. Older membranes make it such that not all static measurement transmitters provide a reliable reading over the long run. Because of this, the diaphragm is susceptible to pressure and mounting position effects, leading to a misalignment of several Pascals with time. Even more crucially, drifts of 1 to 2 Pascal within a year can occur due to an impact on zero-point stability. 

With the use of top-notch sensing technology and electronics, Ziebaq was able to resolve this issue. The bidirectional instruments undergo an automatic mechanical zero point every few hours to guarantee zero-point stability. For this crucial zeroing, you'll need a solenoid valve that, even after years of use, maintains the same pressure on both sides of the diaphragm, providing the highest accuracy and stability level.

Efficient approach for cleanrooms

Older product lines utilized the dynamic measurement principle, although static methods are now more common. It wasn't easy to get the right reading because of the necessary tube length compensation. However, the continuous trend toward miniaturization may render potential tube length effects insignificant, reviving the prospect of dynamic methods. Here at Ziebaq, we make it a point to assess regularly how new technologies impact our core competencies. The potential reintroduction of future product lines for dynamic differential pressure measurement is contingent upon assessing dynamic methods' technical and commercial viability.

Flow and filter monitoring in cleanrooms

To determine how often to service an air conditioner's filter and to draw conclusions about the level of contamination, one measures the differential pressure drop across the filter. The need to detect such minute variations makes a less precise differential pressure instrument suitable for filter monitoring.

Another tool for flow monitoring is differential pressure. One can determine the flow rate as a function of pressure drop across a membrane diffuser or restricting orifice. It may need initial calibration, but it accurately indicates flow velocity in m/s.

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