Cleanroom Environmental Monitoring : Differential Pressure, Temperature, Humidity & Air Velocity
Cleanrooms in semiconductor, pharmaceutical and precision electronics facilities require controlled pressure relationships, stable temperature and humidity, and suitable ventilation conditions. Measurements from appropriate room and duct locations provide a more meaningful view than a single parameter alone.
Monitor room-to-room differential pressure, representative room and duct temperature and humidity, and duct air velocity as separate but related parameters. Together, the measurements support trend analysis and investigations; they do not replace airborne particle classification testing.
Which cleanroom parameters should be monitored?
| Parameter | What it tells you | Typical monitoring point |
|---|---|---|
| Differential pressure (D.P.) | Pressure relationships between adjacent controlled areas | Process areas, corridors and airlocks |
| Temperature / Relative humidity (T / H) | Room conditions versus HVAC supply conditions | Representative room points and supply/return ducts |
| Air velocity (F) | Duct airflow speed and ventilation trends | Suitable supply and return duct sections |
Cleanroom monitoring-point schematic
How can these measurements be interpreted together?
Differential pressure : Track pressure relationships, not cleanliness directly
Positive pressure can help reduce air ingress into selected areas; containment processes may require negative pressure. PMD330 supports room pressure measurement, while the flow-through PMM330 can be considered for suitable HVAC low differential-pressure points.
Temperature and humidity : Compare the room with supplied air
THS301 is a wall-mounted option for representative process-area locations. THS302 is designed for suitable air-duct locations. Comparing trends helps distinguish HVAC supply variations from changes arising inside the room.
Air velocity : Track changes in duct ventilation
FTS34/35 uses heat-transfer changes to obtain air velocity. Install it at suitable duct measurement points. One air velocity value does not directly establish total duct airflow or local unidirectional airflow performance.
Related transmitters and selection considerations
Select instruments by parameter, location, measurement technology and available output configuration. These four transmitter groups cover room pressure, HVAC low differential pressure, room/duct climate and duct air velocity.
PMD330 Differential Pressure Transmitter
Tracks differential pressure across controlled rooms and adjacent spaces to support pressure-relationship monitoring.
- Measurement principle
- Piezoresistive, no flow-through
- Application point
- Adjacent cleanroom zones and airlocks
- Range / configuration
- ±50 ... ±10,000 Pa
PMM330 Differential Pressure Transmitter
A low-pressure measurement option for suitable HVAC applications, subject to range and installation requirements.
- Measurement principle
- Hot-wire, flow-through
- Application point
- General HVAC and low differential-pressure points
- Range / configuration
- ±50 ... ±1,500 Pa
THS301 / THS302 Temperature & Humidity Transmitter
Compares environmental trends at representative process-area points and supply/return air ducts.
- Measurement principle
- Capacitive humidity element and Pt100
- Application point
- THS301 wall-mounted; THS302 duct-mounted
- Range / configuration
- Model-dependent temperature; 0 ... 100%RH
FTS34/35 Air Velocity Transmitter
Measures air velocity through heat-transfer changes for ventilation trend monitoring.
- Measurement principle
- Hot-wire thermal mass measurement
- Application point
- Representative supply/return duct sections
- Range / configuration
- Selectable ranges up to 40 m/s
Examples of monitoring-data interpretation
Pressure is stable, but airflow seems insufficient
Differential pressure represents the relationship between two locations; it cannot establish room-wide airflow distribution. Review ventilation equipment, duct velocities and local airflow conditions separately.
Room temperature rises while supply-air temperature stays steady
Compare THS301 room trends with THS302 duct trends, and review equipment load and airflow conditions to narrow the potential cause of the deviation.
Frequently asked questions
Do all cleanrooms require positive pressure?
No. Pressure direction depends on the process and contamination-control objective. Containment applications may require negative pressure.
Does normal differential pressure confirm cleanroom cleanliness?
No. Differential pressure, velocity and airborne particle concentration represent different measurements. Cleanliness classification requires the applicable particle testing.
How should cleanroom transmitters be selected?
Define the parameter and monitoring point first, then check measurement range, accuracy, mounting, medium and output requirements against the latest product datasheet.
Technical note : Differential pressure, temperature, humidity and air velocity transmitters provide environmental data. They do not replace airborne particle concentration testing or classification required under applicable cleanroom standards.