Meteorological Sensors

Air temperature and humidity

Temperature and relative humidity are usually measured by one combined probe, with dew point, wet bulb and the rest derived from them — either in the sensor or in the software behind it. The probe has to be shielded: direct sun on a bare element reads high by several degrees, so a radiation shield is part of the measurement rather than an accessory to it.

Heated probes are specified where icing or persistent condensation would otherwise corrupt the reading, and intrinsically safe versions where the mast sits in a classified area.

Barometric pressure

Pressure sensors are judged on long-term stability rather than headline accuracy — a barometer that drifts a hectopascal a year is a barometer that quietly misreports deck level. Instruments meeting WMO and air-traffic requirements are used offshore, often with two or three independent pressure elements cross-checking one another so that drift shows up before it matters.

Wind blowing across a pressure port creates an error of its own, so a static pressure head or pressure choke is fitted on exposed installations, and hand-held reference instruments are used to check a barometer in place.

Beyond the basics

The same package often carries further parameters: rainfall, solar radiation, sea temperature by non-contact infrared, water level, snow depth, and distance or angular measurements. We specify and supply these on request as part of a wider environmental monitoring system.

What matters offshore

• Hazardous area. Where the met mast sits inside a classified zone, intrinsically safe temperature, humidity and pressure sensors are used, sharing an Ex e junction box.
• Salt and corrosion. Shields, housings and fixings are specified for a marine atmosphere. An instrument that is perfectly good on a coastal met station may not last a year on a platform.
• Calibration and verification. Pressure and humidity both drift, so a calibration interval is part of owning the instrument. Calibration is a laboratory activity — the manufacturer or a certified laboratory issues the certificate — and we manage the return on your behalf. On site we verify the installed system against recently calibrated references, which is a different activity producing a different document: see calibration versus system verification.