Vaisala DMT152 Dew Point Transmitter

Overview

Vaisala DMT152 is a DRYCAP dew point transmitter designed for measuring low dew point in OEM applications, down to −80 °C (−112 °F). It uses the Vaisala DRYCAP 180U thin-film polymer sensor, which gives long-term stability and survives condensation, so it can be installed in compressed air systems, dryers and dry gas lines without long recovery times after a wet event. The dew point range is −80 to −20 °C with accuracy of ±2 °C Td below −40 °C and ±3 °C from −40 to −20 °C.

Seven Star LLC supplies the Vaisala DMT152 to compressed air, gas and drying equipment users and to OEM builders in Oman and the GCC, with engineering support in Muscat. In plants where humidity and temperature are already tracked with the Vaisala HMT330 humidity and temperature transmitter, the Vaisala DMT152 extends monitoring to the dry end, where relative humidity is no longer a useful measure and dew point is the correct quantity.

DRYCAP Measurement Principle

The DRYCAP 180U sensor is a capacitive polymer element that absorbs water molecules in proportion to the water vapour pressure of the gas. The transmitter converts the capacitance to dew point temperature, and when the dew point is below 0 °C it outputs frost point. Because the sensor is a solid polymer layer rather than a chilled mirror or aluminium oxide element, it responds quickly and tolerates condensation and wetting. Self-diagnostics run continuously, and purge status can be signalled on an output.

Response time at +20 °C and 1 bar is stated as 2 seconds to reach 63 percent and 5 seconds to reach 90 percent for a rise from −80 to −20 °C Td, and 0.5 minutes and 7.5 minutes for a fall from −20 to −80 °C. Typical long-term stability is better than 2 °C per year, so the calibration interval can be long. The datasheet also gives concentration by volume from 0 to 500 ppm, with accuracy of ±(0.2 ppm + 20 percent of reading) at +20 °C and 1013 mbar, which is useful for gas purity work.

Engineering Design of the Vaisala DMT152

The Vaisala DMT152 housing and wetted parts are AISI 316L stainless steel, with a 18 micron stainless steel mesh filter, IP66 protection against dust and splashed water and a weight of 190 g in the ISO G1/2 version. Process connections are ISO G1/2, NPT 1/2, UNF 3/4-16 or UNF 5/8-18, so the transmitter fits existing sample points. It operates from −40 to +70 °C and handles pressures from 0 to 50 bar (725 psia), with sample flow rate having no effect on accuracy.

Two scalable analog outputs, 4 to 20 mA, 0 to 20 mA, 0 to 5 V or 0 to 10 V, are available together with an RS-485 digital output, and alarm-level or purge information can be indicated by an analog signal or an LED. Operating voltage is 11 to 28 V DC for RS-485, 15 to 28 V DC for voltage output and 21 to 28 V DC for current output. Accessories include a sampling cell in several versions, a loop-powered external display, a USB cable for PC connection and a cable for the MI70 handheld indicator. Not suitable for hydrogen or pure carbon dioxide.

Key Features

Main strengths of the Vaisala DMT152 in low dew point monitoring:

• Dew point measurement down to −80 °C Td with accuracy of ±2 °C below −40 °C, from a compact OEM-sized transmitter.
• DRYCAP polymer sensor withstands condensation and offers excellent long-term stability, with drift typically better than 2 °C per year.
• Operation at pressures up to 50 bar means direct installation in compressed air and gas lines with no need for pressure reduction.
• Fast response of 2 seconds to 63 percent when the dew point rises from −80 to −20 °C shortens alarm delay.
• Two scalable analog outputs and RS-485 digital output suit PLCs, DCS systems and OEM electronics.
• Stainless steel AISI 316L housing, IP66 rating and four thread options fit harsh industrial environments and existing fittings.
• Accurate also in the difficult combination of low humidity and hot air found in plastics drying.
• Traceable calibration certificate is included, and a long calibration interval keeps maintenance cost low.

Industrial Applications

The manufacturer lists air and plastics dryers, dry chambers, dry gases, high-voltage circuit breakers, semiconductor manufacturing, research and testing and compressed air as typical areas. In the Gulf, compressed air quality matters for instrument air systems on oil and gas sites, where moisture causes corrosion of pneumatic positioners and freezing in cold conditions, and for high-voltage circuit breakers in power substations.

Seven Star LLC supports plant engineers across Sohar, Duqm, Salalah and Muscat with selection of the DMT152 connection thread, sampling cell and output type, and with comparison against other dew point instruments such as the Michell Easidew EA2 dew point transmitter and the CS Instruments FA 510 dew point sensor. We can send the Vaisala DMT152 datasheet to help your team define installation and calibration planning.

Technical Specifications

Specifications of the Vaisala DMT152 are summarised from the manufacturer datasheet. Dew point accuracy depends on gas temperature, so check the graph in the datasheet.

Request a Quote for Vaisala DMT152

To request a quotation for the Vaisala DMT152, tell Seven Star LLC the process connection, output type, operating pressure and any sampling cell or display you need. We supply the Vaisala DMT152 with engineering support in Muscat and can provide the Vaisala DMT152 datasheet and accessory information to engineering and procurement teams across Oman and the GCC.