Differential Pressure Measurement in Cleanrooms.

Differential pressure measurement is a crucial aspect of maintaining optimal conditions in cleanrooms where controlled environments are essential for the production of pharmaceutical products for example. This blog explores the measurement technology used, the distinctions between building management systems (BMS) and environmental monitoring systems (EMS), and the typical installation locations for differential pressure devices, with a primary focus on cleanroom monitoring.

Measurement Technology

Thermal Measuring Principle

The thermal measuring principle relies on a heating element that is placed between two temperature-sensitive resistors. A gas flow shifts the temperature profile in the direction of one resistance, which can be measured and the differential pressure evaluated.

Membrane Measuring Principle

Membrane-based differential pressure measurement relies on the deformation of a membrane or diaphragm when subjected to different pressures on either side. Key devices include:

• Capacitive Sensors: These use a membrane that changes capacitance as it deforms under pressure.
• Piezoelectric Sensors: These generate an electric charge in response to mechanical stress on the membrane.
• Resistive Sensors (Strain Gauges): These measure the change in electrical resistance as the membrane deforms.

Membrane-based devices are known for their accuracy and sensitivity, making them ideal for applications requiring precise pressure measurements.

Thermal vs. Membrane Overview

When measuring differential pressure and the reference 0 point is daisy chained via multiple devices, then only membrane sensors should be used and not thermal mass sensors. The thermal mass sensor leaks per design and as of such is not designed for this application.

Building Management System (BMS) vs. Environmental Monitoring System (EMS)

While both BMS and EMS are crucial for maintaining the integrity of pharmaceutical environments, they serve different purposes and operate differently.

Building Management System (BMS)

• Function: BMS is designed to manage and control the building's mechanical and electrical equipment, including HVAC (Heating, Ventilation, and Air Conditioning) systems, lighting, fire systems, and security systems.
• Scope: It has a broader scope, encompassing the entire building infrastructure.
• Monitoring: Primarily focuses on the overall performance and energy efficiency of building systems.

Environmental Monitoring System (EMS)

• Function: EMS specifically monitors environmental conditions critical to pharmaceutical production, such as temperature, humidity, and differential pressure in cleanrooms.
• Scope: It is more focused and specialized compared to BMS, ensuring compliance with industry standards and regulations (e.g., GMP, ISO).
• Monitoring: Provides real-time monitoring and logging of environmental parameters to ensure product safety and quality.

Installation of Differential Pressure Devices

Differential pressure devices are traditionally installed in various locations within pharmaceutical facilities to ensure proper environmental control. Key areas include:

Cleanrooms

Cleanrooms are highly controlled environments where differential pressure is critical to preventing contamination. Devices are installed to:

• Monitor Pressure Differentials: Between different cleanroom zones (e.g., from a higher classification area to a lower classification area) to ensure that air flows from cleaner to less clean areas.
• Maintain Airflow Direction: By ensuring that air moves from areas of higher pressure to areas of lower pressure, preventing the ingress of contaminants.

Airlocks and Pass-Through Chambers

These areas act as buffer zones between cleanrooms and less controlled areas. Differential pressure devices ensure that these spaces maintain the correct pressure differential to prevent contamination during the transfer of materials or personnel.

HVAC Systems

Differential pressure sensors are integrated into HVAC systems to monitor and control the pressure within ductwork, ensuring that the system maintains the required pressure levels in various parts of the facility.

Cleanroom Pressure Levels

In cleanroom environments, maintaining specific pressure differentials is critical. Typical pressure levels are:

• ISO 7 Cleanroom: +10 to +20 Pascals (Pa) relative to adjacent areas.
• ISO 8 Cleanroom: +5 to +15 Pa relative to adjacent areas.
• Airlocks: Typically maintained at +5 to +10 Pa relative to the cleanroom to ensure a pressure gradient that prevents contamination.

By carefully monitoring and controlling differential pressures, pharmaceutical facilities can maintain the stringent environmental conditions required for the production of safe and effective products.

Rotronic Product Range

Differential Pressure Transmitter - Rotronic PF4/5
Clean Room Panel - Rotronic CRP5
Differential Pressure Probe - Rotronic RMS PCD-S

Installation

Traditionally, the differential pressure sensors will be installed in the area where the air handling units are located, as it is easier for maintenance and calibration purposes. PST offer a range of cabinets for improved access:

Conclusion

Differential pressure measurement is an indispensable part of the pharmaceutical industry, ensuring that cleanrooms and other critical areas maintain the necessary conditions for product quality and safety. Understanding the technology behind these measurements, the differences between BMS and EMS, and the strategic installation of differential pressure devices provides a comprehensive view of how pharmaceutical environments are controlled. This knowledge is crucial for professionals aiming to uphold the highest standards in pharmaceutical manufacturing.

Need more information?

Check out our videos to find out more:

Differential Pressure Measurement
CRP5 Cleanroom Panel
Environmental Monitoring

Related Information

Cleanroom and Chamber Monitoring
BMS and EMS Monitoring
BMS and EMS Integration Made Easy
BMS, EMS & GMP in Pharmaceutical Production
HVAC & Building Automation
Room Differential Pressures in Facility Design: Fundamentals (ISPE)