Ambient pressure sensor enclosure rain protection

Use an externally exposed, sealed absolute-pressure sensor when you need ambient pressure without making the enclosure breathe. Use an internal sensor behind a rated pressure-equalization vent when its response remains adequate during rain and temperature changes. The membrane material is usually described as a hydrophobic microporous membrane, but loose membrane material is not a complete sealing solution. Choose between the two approaches by following the pressure path, including what happens when that path gets wet.

Compare the two pressure paths

An external-pressure sensor puts its sensing face outside while a specified seal separates that face from the enclosure interior. A vented design admits air through a protective membrane, allowing an internal sensor to follow outside pressure.

Neither approach automatically preserves the original enclosure rating. Our enclosure ratings are manufacturer ratings; our enclosures are not UL listed. Component markings must be checked against the complete installed design.

Where an external sensor wins

An external sensor is usually the clearer choice when pressure measurement must remain independent of enclosure temperature and volume. Specify an absolute-pressure sensor intended for atmospheric measurement, with an exposed face suitable for the expected water contact.

Absolute pressure uses an internal reference rather than enclosure air as its zero reference. A gauge or differential sensor may reference another port, so confirm where every pressure connection leads.

Water resistance alone does not establish measurement suitability. Check atmospheric-range accuracy, resolution, temperature compensation, and allowable exposure at the sensing face. A sensor suitable for measuring liquid depth may not provide the required barometric accuracy.

The mounting design must also separate the wet side from the dry side. Follow the sensor manufacturer's seal geometry, surface finish, compression, and tightening requirements. Sealing around a circuit board does not necessarily seal the sensor package or its electrical connections.

Keep water from standing against the pressure-sensitive face. For freshwater, a 0.4 in [10 mm] water column adds approximately 98 Pa, or 0.98 hPa. That is a measurement offset even when no water enters the enclosure.

Mechanical installation can also shift readings. If the output changes after tightening or thermal cycling, investigate pressure sensor drift in metal housings before changing calibration.

Where a membrane vent wins

A vented design can suit a protected internal sensor when pressure changes slowly enough for the enclosure to follow. It also provides pressure equalization for the enclosure itself, rather than only exposing one sensing face.

Choose a complete vent assembly with documented installation conditions. The membrane, support structure, mounting seal, and enclosure wall interface all matter. A mesh screen may stop insects or debris, but it is not equivalent to a liquid-water barrier.

Hydrophobic membranes resist liquid-water entry within their specified conditions while allowing gas transfer. Their performance depends on pore structure, area, contamination, and pressure differential. Some applications also require resistance to oils or chemicals that can wet an otherwise water-repellent membrane.

Use the pressure-equalization membrane vent selection article for those component-selection details. For pressure measurement, the additional question is how quickly the installed enclosure follows ambient pressure.

A larger enclosure generally needs more airflow than a smaller enclosure for the same pressure response. Internal heating, blocked membrane area, or a restrictive protective cover can increase the difference between inside and outside pressure.

Do not treat this airflow as useful cooling or assume it keeps the interior dry. The separate article on pressure-vent humidity and heat limits explains those boundaries.

Choose for the actual rain exposure

For wind-driven rain, place either pressure interface away from direct runoff and splash where its instructions permit. A downward-facing interface or shield can reduce exposure, but cannot establish a rating by itself.

Wind also changes the pressure being sampled. At an air density of 1.2 kg/m³, wind at 33 ft/s [10 m/s] has a dynamic pressure of approximately 60 Pa. That equals 0.6 hPa, although the actual port error depends on orientation and surrounding geometry.

This matters when your allowable error is around 1 hPa. Protecting a sensor from rain while placing it in a strong local airflow can exchange one measurement error for another. Use a documented static-pressure inlet arrangement when wind-induced error matters.

For persistent wetting, an exposed membrane may temporarily lose much of its effective airflow. An external sensor may avoid that enclosure-equalization delay, but water sitting on its face can still distort the reading.

For possible immersion, specify depth, duration, and measurement requirements separately. An IP67 component marking does not establish unrestricted rain, hose, or continuous-immersion suitability for the assembled enclosure. A vent cannot exchange air normally while its outside face is submerged.

The article on breather vents and enclosure ratings covers the installation evidence needed before retaining a stated enclosure type. Apply that review to the sensor penetration as well as the vent alternative.

Check pressure response before release

Set an error budget before selecting hardware. For example, a project requiring ambient pressure within ±1 hPa permits only ±100 Pa total error. Sensor accuracy, temperature effects, wind exposure, water loading, and pressure lag must share that allowance.

Internal heating can overwhelm that budget in an unvented box. For dry air initially at 1,013 hPa and 68°F [20°C], warming a rigid, sealed volume to 86°F [30°C] raises pressure by approximately 35 hPa. This ideal-gas calculation assumes constant volume and no leakage.

For the vented option, check response using the actual free air volume and installed vent arrangement. Airflow quoted at one pressure differential does not directly establish response near atmospheric equilibrium. Use enclosure pressure vent sizing for rapid temperature changes for the sizing considerations.

A useful validation sequence is:

• Compare both sensor arrangements against a suitable reference under dry, stable conditions.
• Apply a controlled pressure change within the equipment's specified limits and record settling time.
• Cycle internal equipment power to reveal errors caused by enclosure heating.
• Repeat the response check during representative rain exposure, including wet shields and vent surfaces.
• Inspect for ingress and repeat accuracy checks after drying and thermal cycling.

Use a qualified test facility where formal ingress validation is required. Keep electrical equipment de-energized during water testing unless an approved test procedure specifically requires otherwise.

What to specify

Choose the sensing arrangement before releasing the enclosure drawing. Moving from a vent to a bulkhead sensor later can change the hole diameter, sealing surface, internal clearance, and cable route.

Send these requirements with the enclosure request:

• Measurement: absolute ambient pressure, operating range, total allowable error, and maximum settling time.
• Exposure: rain direction, wind, runoff, possible standing water, immersion risk, temperature range, and cleaning chemicals.
• Pressure interface: exact sensor or vent drawing, permitted orientation, protective shield, and maintenance access.
• Cutout: diameter, tolerance, location, wall thickness limits, edge clearance, and required sealing-surface finish.
• Installation: seal material, compression requirements, tightening instructions, electrical connection, and cable support.
• Enclosure: material, width, height, depth, required enclosure type, and any project listing requirement.
• Verification: pressure-response acceptance criteria and the evidence required for the completed assembly's ingress protection.

We build custom enclosures with customer-defined material, dimensions, and cutouts, starting from one piece. Submit the selected interface drawing rather than requesting a generic breathing hole. The drawing review must confirm whether the proposed penetration fits the specified enclosure design.

Use the enclosure selector when environment, listing requirements, and usable space are ready to narrow the enclosure choice. Dimensional fit does not establish pressure accuracy or thermal suitability.

For most rain-exposed measurement jobs, prefer the sealed external sensor when response independence is the main requirement. Prefer the vented internal sensor when measured wet-weather response meets the error budget and enclosure pressure equalization is also needed.

Enclosures for this job

Catalog sizes that suit the job this article answers, picked from its subject; open one for its full specifications.

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