Vaisala HMP7 Humidity and Temperature Probe

Overview

Vaisala HMP7 is a relative humidity and temperature probe designed for applications with constant high humidity or rapid humidity changes, such as drying and test chambers, combustion air, humidifiers and meteorological measurement. Relative humidity accuracy is up to ±0.8 %RH at +23 °C from 0 to 90 %RH, temperature accuracy is up to ±0.1 °C, and the probe head works from −70 to +180 °C. Each probe is delivered with a traceable calibration certificate, with six points for humidity and one for temperature.

Seven Star LLC supplies the Vaisala HMP7 to process plants, test laboratories and HVAC and energy teams in Oman and the GCC, with engineering support in Muscat. Where the Vaisala HMT330 humidity and temperature transmitter serves as a wall or duct instrument, the Vaisala HMP7 is the choice for locations that are hotter, wetter or at pressure, and it can be used on its own or connected to Indigo series transmitters.

High-Humidity Measurement Principle

The Vaisala HMP7 relies on HUMICAP thin-film capacitive sensors, in R2, R2C or 180VC versions, which respond to the water vapour content of gas around them. A Pt100 RTD of class F0.1 measures temperature at the same point. In very humid air the main risk is condensation on the sensor, which makes readings jump or lag. The probe solves this by heating the whole probe head, not only the sensor, so that the head stays above the dew point temperature of the process and condensation cannot form.

Heating can be combined with a temperature compensation value. When the process temperature is measured with a TMP1 temperature probe, the HMP7 can show true relative humidity at process temperature while the probe head is warmer and dry. Chemical tolerance and long-term stability are improved by the sensor purge feature, available with the R2C and 180VC sensors, which helps keep the sensor free of contaminants. The 180VC sensor is also resistant to hydrogen peroxide, although accuracy is not specified below −20 °C with it.

Engineering Design of the Vaisala HMP7

The Vaisala HMP7 is built vapour and pressure proof, with a probe body rated IP66, operation at pressures below 10 bar and a measurement environment that can be air, nitrogen, hydrogen, argon, helium, oxygen or vacuum. The probe body operates from −40 to +80 °C while the head tolerates −70 to +180 °C and dew points up to +100 °C. The T63 response time is 15 seconds, and the probe suits outdoor use.

Electrically the Vaisala HMP7 is a digital probe operating from 18 to 30 V DC with a typical current of 10 mA and a maximum of 500 mA during heating, and it provides an RS-485 output running Modbus RTU. It can serve as a standalone transmitter on a serial bus, or it can be connected to Indigo transmitters, which display the readings and send them to automation systems through analog signals, relays or Ethernet, with cable lengths of up to 30 metres between probe and transmitter. The Indigo80 handheld indicator and Insight PC software provide field calibration and diagnostics.

Key Features

Key advantages of the Vaisala HMP7 for demanding humidity measurement:

• Relative humidity accuracy up to ±0.8 %RH and temperature accuracy up to ±0.1 °C suit tests where small differences matter.
• Probe head heating prevents condensation at extreme humidity and allows measurement close to saturation.
• Wide temperature range of −70 to +180 °C at the probe head covers cold chambers and hot process air.
• Vapour and pressure proof construction works at pressures below 10 bar and in gases such as nitrogen, hydrogen, argon and helium.
• Sensor purge on selected sensors improves long-term stability and chemical resistance in contaminated air.
• Modbus RTU over RS-485 makes it easy to connect to PLCs, data loggers and building management systems.
• Compatible with the Vaisala Indigo product family and Insight PC software for display, relays, configuration and calibration.
• A traceable calibration certificate with six humidity points and one temperature point is supplied with every probe.

Industrial Applications

The HMP7 serves drying and test chambers, combustion air, humidifiers and meteorological measurements, where performance and chemical tolerance matter. In practice this covers environmental chambers for electronics testing, kilns and dryers, turbine inlet air monitoring, humidified process air in food and pharmaceutical plants and climate control for cleanrooms. In Oman, plants along the coast at Sohar, Duqm and Salalah face high humidity and dew points close to ambient, a condition where heated probes keep their accuracy.

Seven Star LLC assists engineers with selecting the sensor version, cable length and Indigo transmitter for the HMP7, including probe mounting kits and filters. Teams that also need a dedicated dew point sensor can compare it with the Michell Easidew EA2 dew point transmitter or the Siemens QFM1660 duct humidity and temperature sensor. Please request the Vaisala HMP7 datasheet if you want the full accuracy-over-temperature charts and the list of calculated output parameters.

Technical Specifications

Specifications of the Vaisala HMP7 are summarised from the manufacturer datasheet. Accuracy figures include non-linearity, hysteresis and repeatability.

Request a Quote for Vaisala HMP7

To request a quotation for the Vaisala HMP7, tell Seven Star LLC the sensor version, cable length, transmitter or logger and any mounting hardware you need. We supply the Vaisala HMP7 with engineering support in Muscat and can share the Vaisala HMP7 datasheet and calibration certificate details with engineering and procurement teams across Oman and the GCC.