Vaisala
Reading the Pressure Between Spaces

Cleanroom pressure problems are rarely obvious. The pressure difference between two adjoining spaces may be just 5, 10 or 15 pascals, but even a small difference matters because it keeps the air flowing from cleaner rooms toward areas with a higher contamination risk.

Vaisala’s differential pressure transmitters measure these small shifts accurately, helping pharmaceutical, biotechnology, medical device and semiconductor facilities confirm that the required pressure relationships are being maintained.

Everyday activity can briefly disrupt this balance. Opening a door, operating an airlock or moving between rooms may cause a momentary pressure reversal. This does not necessarily mean the environment is out of control. The challenge is determining whether the change was temporary or continued long enough to require attention. Reliable measurements help teams set meaningful alarms, investigate deviations and prepare documentation using a shared record of what occurred.

At critical room boundaries, Vaisala uses direct room-to-room measurement. A single transmitter connects its high and low pressure ports to the spaces on either side of the boundary and measures the difference between them. An alternative approach is to calculate the difference using two separate pressure readings, but this can increase uncertainty, especially when the readings are not taken at exactly the same time. Measuring the difference directly gives clients more dependable information for contamination control, deviation investigations and production decisions.

Engineering Repeatable Measurement

The PDT102 brings this level of precision to life science and high-technology cleanrooms using a micromachined MEMS silicon sensor. At its core is an ultrathin silicon diaphragm that detects very small pressure changes while delivering repeatable results and long-term stability. Its sensitive yet durable design captures minor shifts consistently, giving monitoring teams a clear reading.

The PDT102 is available with accuracy levels of either 0.25 percent or 0.50 percent of span, so users can select the option best suited to their application. Before leaving the factory, each unit goes through a nine-point calibration that is traceable to standards maintained by the U.S. National Institute of Standards and Technology. A calibration certificate is supplied with the transmitter, giving regulated facilities a documented basis for verifying accuracy and tracking performance over time.

Technicians can calibrate the PDT102 where it is installed using the optional process valve actuator and test jacks, without disconnecting the process tubing. Front-mounted zero and span controls provide easy access for adjustments, while the slim housing fits neatly onto a DIN rail. These design choices simplify routine servicing and reduce disturbance around controlled areas, helping facilities maintain reliable measurements throughout the transmitter’s working life.

Matching Instruments to Applications

The PDT101 is available in bidirectional and unidirectional models, allowing facilities to choose the version that fits their application. Bidirectional models measure the small positive and negative pressure differences commonly found in regulated cleanrooms, life science facilities and data centers. Unidirectional models are designed for air-handling units, where they can monitor pressure across fans. This gives each environment a suitable configuration rather than relying on a single model for every setting.

Installers can choose from three pressure ranges, expressed in pascals or inches of water, as well as current or voltage output. The transmitter can be mounted on a wall, panel or DIN rail to suit different facility and cabinet layouts. Detachable connectors, brass tubing connections and accessible adjustment potentiometers make installation and servicing more straightforward. An LED status indicator also allows technicians to confirm power at a glance, which can save time during commissioning and troubleshooting.

PDT101 measurements are traceable to international standards, giving facilities a clear basis for trusting the results they record. This is especially valuable in regulated environments, where teams may need to demonstrate both what was measured and how its accuracy was verified. With its compact size and models designed for different applications, the PDT101 works well in regulated areas and air-handling systems. It also gives installers greater flexibility while providing the reliable records required for regular reviews, calibration planning and environmental control.

Connecting Measurement and Evidence

A pressure transmitter provides greater value when its readings feed directly into a monitoring system that helps teams respond. Vaisala’s CAB100 cabinet brings signals from the PDT101 or PDT102 together with data loggers and other environmental measurements. It can be supplied preconfigured for a cleanroom, fitted with safety barriers when needed and powered through an integrated mains supply or Power over Ethernet. With the equipment housed in one enclosure near the measurement points, facilities can reduce onsite assembly and keep their instrumentation organized.

Placing the pressure transmitter close to the data logger also keeps wiring runs short. This limits the effect of wiring on analog signals and reduces the chance of measurement error. The CAB100 connects the instruments to Vaisala’s viewLinc Continuous Monitoring System. A single compact cabinet can collect differential pressure, temperature, humidity and other parameters, avoiding the need to install separate components throughout the facility. Data follows a clear path from the room boundary to a centralized record.

In viewLinc, teams can see current readings, examine historical trends, manage alarms and generate reports with audit trails. Remote access allows authorized personnel to review conditions without entering the cleanroom, and the system can support thousands of monitored locations as requirements expand. Through OPC UA connectivity, compatible systems can also retrieve current and historical data without custom programming. Although environmental control and compliance monitoring can remain separate, quality, validation and facilities teams can work from the same reliable source of information.

Turning Records Into Confident Action

LSNE, now part of PCI Pharma Services, offers a practical example of the CAB100’s space-saving design. Plant engineer Dan Gabrault estimated that a conventional cleanroom monitoring system would require about four times as much space. Because the cabinet is compact and arrives preconfigured, it is easier to install in clean areas where equipment must be kept to a minimum. The project shows that Vaisala has considered not only measurement performance but also the physical constraints facilities face during installation.

After the system is running, teams can monitor pressure patterns, set appropriate alarm delays and review what happened before and after a deviation. For example, they can identify a brief pressure drop caused by an open door and distinguish it from a continuing loss of pressure that requires action. Reports and audit trails retain the sequence of events for future review. This gives users more than a stream of readings. It provides clear evidence that supports timely responses and well-informed decisions.

Vaisala’s strength lies in connecting every part of the measurement process. Its silicon sensors detect minute pressure differences, purpose-built transmitters meet the needs of cleanrooms and air-handling systems and centralized monitoring turns the readings into reliable records. With this information, clients can maintain the intended direction of airflow, improve contamination control and avoid unnecessary interruptions to production. This end-to-end performance supports Vaisala’s recognition as one of the Top Pressure Transmitter Manufacturing Companies in Europe 2026.