Vaisala HMT330 Humidity and Temperature Transmitter

Overview

The Vaisala HMT330 is a series of industrial humidity and temperature transmitters built on Vaisala’s proprietary HUMICAP® sensor technology, designed for demanding process measurement where stable, long-term accuracy is essential. Offered in multiple probe configurations for wall-mount, duct, high-pressure, high-temperature, and pressurized-pipeline installations, the HMT330 family measures relative humidity from 0–100 %RH and temperature up to +180°C depending on model, making the Vaisala HMT330 one of the most versatile industrial humidity transmitter platforms available.

With engineering support in Muscat, Seven Star LLC supplies Vaisala HMT330 transmitters to industrial customers across Oman and the GCC, with NIST-traceable factory calibration and technical support for probe selection suited to regional process conditions.

Operating Principle

The HMT330 measures relative humidity using Vaisala’s HUMICAP® thin-film polymer capacitive sensor, in which a thin polymer layer absorbs and releases water vapor in proportion to the surrounding relative humidity, changing the sensor’s capacitance in a precisely characterized way. This capacitive measurement principle responds quickly to humidity changes, is immune to particulate contamination, and tolerates exposure to most industrial chemicals without permanent damage to the sensing element – a key advantage over resistive or mechanical humidity sensing methods that degrade under contamination.

Temperature is measured independently using a Pt100 RTD sensor to Class B tolerance, and the two measurements are combined internally to calculate derived parameters including dewpoint temperature, mixing ratio, absolute humidity, wet bulb temperature, enthalpy, and water vapor pressure, depending on the ordered configuration. For applications with high chemical concentrations or condensing conditions, selected HMT330 models offer a chemical purge or warmed-probe function that periodically heats the sensor to drive off contaminants and maintain calibrated accuracy between service intervals, extending the useful life of the sensing element without manual intervention.

Engineering Design of the Vaisala HMT330

The Vaisala HMT330 transmitter body is housed in a corrosion-resistant IP65-rated (NEMA 4) aluminum enclosure, with the interchangeable HUMICAP® probe connected via a sealed cable gland or industrial connector depending on the model variant. The transmitter can be ordered with an optional graphical LCD display that shows real-time readings alongside a one-year measurement trend history, allowing technicians to spot drift or process excursions directly at the instrument without needing separate data-logging equipment.

Installation is straightforward: the transmitter body mounts to a wall, pole, or DIN rail using the appropriate accessory kit, while the probe itself is selected based on application – a duct-mount probe with flange kit for HVAC ducting, a warmed stainless-steel probe for high-humidity or condensing process lines, or a pressure-rated probe with ISO or NPT threaded fitting for pressurized vessels up to 100 bar. Wiring connects to the transmitter’s terminal block for power (10–35 VDC or 24 VAC) and up to three configurable analog outputs, with optional RS-232, RS-485, or relay outputs for digital integration.

Key Features

The HMT330 series delivers industrial-grade humidity and temperature measurement with configuration flexibility across a wide range of process conditions:

• Vaisala HUMICAP® capacitive sensor delivers stable, repeatable relative humidity measurement from 0 to 100 %RH.
• Multiple probe variants support wall-mount, duct, high-pressure, high-temperature, and pressurized-pipeline installations from a single transmitter platform.
• Temperature measurement accuracy of ±0.2°C at +20°C using a Pt100 RTD Class B sensor.
• Optional chemical purge and warmed-probe functions maintain accuracy in harsh chemical or condensing environments.
• Corrosion-resistant IP65 (NEMA 4) aluminum housing suits demanding industrial and outdoor installation locations.
• Graphical LCD display option shows real-time readings and up to one year of measurement trend history on-device.
• Up to three configurable analog outputs plus optional RS-232, RS-485, and relay outputs for flexible system integration.
• Factory calibration at six humidity points with NIST-traceable certificate included as standard.

Industrial Applications

The Vaisala HMT330 humidity and temperature transmitter is deployed across HVAC and building management systems, compressed air dew point monitoring, pharmaceutical cleanrooms, power plant flue gas and inlet air monitoring, and industrial drying processes where accurate, drift-resistant humidity measurement is critical to product quality and process efficiency. Its range of probe options makes it equally suited to a district cooling plant’s duct network or a high-pressure process vessel in a petrochemical facility.

Backed by manufacturer datasheet documentation, Seven Star LLC distributes genuine HMT330 transmitters to instrumentation and process teams throughout Oman and the GCC, supporting humidity-critical operations in RO desalination plants, pharmaceutical manufacturing, hospitality and hospital HVAC systems, and industrial facilities across the Sohar and Salalah economic zones. Regional calibration support and genuine sourcing ensure NIST-traceable accuracy is maintained throughout the instrument’s service life, protecting process quality decisions that depend on trustworthy humidity data.

Technical Specifications

The table below summarizes the key specifications of the Vaisala HMT330 series humidity and temperature transmitter, confirming why the Vaisala HMT330 remains a benchmark instrument for industrial humidity measurement.

Request a Quote for Vaisala HMT330 Humidity and Temperature Transmitter

To request a formal quotation for the Vaisala HMT330 humidity and temperature transmitter, contact Seven Star LLC’s instrumentation division directly.Seven Star LLC supplies this item on request with the manufacturer documentation, and availability and lead time are confirmed at quotation. Working closely with plant engineers in the region, Seven Star LLC supplies the probe with manufacturer documentation and application support for selecting the correct probe configuration for your process.

Browse the full Vaisala range or see more Temperature Instrumentation products supplied by Seven Star LLC in Oman and the GCC.