Vaisala DMT143 Dew Point Transmitter

Overview

The Vaisala DMT143 is a miniature DRYCAP® dew point transmitter designed for compressed air dryers, plastic resin dryers and other OEM equipment where space is tight but dry-gas quality still has to be proven continuously. Built around the DRYCAP 180D thin-film polymer sensor, it covers a typical dew point range of −70 to +60 °C (Td/f) with a stated accuracy of ±2 °C in air or nitrogen, and it can be screwed straight into pressurized lines up to 50 bar absolute. Its stainless steel AISI 316L body weighs only around 90 g, which makes it one of the most compact ways to add a traceable moisture measurement to a skid or a dryer outlet.

Seven Star LLC supplies the Vaisala DMT143 to plant engineers, OEM panel builders and maintenance teams across the Sultanate of Oman and the wider GCC, with engineering support in Muscat. We help customers select the right thread, output and alarm option, and we keep the datasheet, accessories list and sampling-cell options ready for fast technical review.

Measurement Principle

DRYCAP technology measures moisture with a capacitive thin-film polymer sensor whose dielectric properties change as water molecules are absorbed. The electronics convert that capacitance into dew point or frost point temperature and water concentration in ppm by volume. When the dew point is below 0 °C, the Vaisala DMT143 reports frost point for Td/f, which is the physically meaningful value for very dry gas. According to the manufacturer, the sensor withstands condensation completely, so a water slug during a dryer failure or a cold start does not destroy it, and it is highly resistant to particulate contamination, oil vapor and most chemicals. Measurement accuracy is not affected by the sample flow rate.

The key feature that separates the Vaisala DMT143 from simple polymer humidity probes is Vaisala’s autocalibration function. During operation the transmitter periodically heats the sensor, checks for dry-end drift and automatically corrects the calibration curve. This self-diagnostic cycle is why the typical calibration interval of the Vaisala DMT143 is two years, and why the instrument stays usable at very low dew points where ordinary polymer sensors tend to drift. During the self-diagnostic phase the supply current rises to a pulsed 220 mA (typical), which is worth noting when sizing a power supply for several transmitters.

Engineering Design of the Vaisala DMT143

Mechanically the Vaisala DMT143 is a short cylindrical stainless steel transmitter with the sensor protected by a sintered stainless steel filter. Four process connection options are listed in the datasheet: ISO 228-1 G1/2", 1/2" NPT, 3/4"-16 UNF and 5/8"-18 UNF. The G and UNF versions weigh 90 g and the NPT version 100 g. The housing is rated IP66, the operating temperature range is −40 to +60 °C and the operating pressure range is 0–50 bar absolute. For operation below 0 °C or above 20 bar absolute, the supply voltage must be 24–28 V DC.

Electrical connection of the Vaisala DMT143 is through a 4-pin M8 connector. The scalable analog output can be ordered as 4–20 mA (3-wire), 0–1 V, 0–5 V or 1–5 V, alongside a non-isolated RS-485 digital output that supports Modbus RTU and the Vaisala Industrial Protocol. An LED alarm indicates when the dew point exceeds a factory-preset trigger point, which can later be changed with Vaisala Insight PC software. The same software and the Indigo80 handheld indicator can be used to configure the transmitter and to view and log data.

Key Features

The main engineering advantages of the Vaisala DMT143 for dryer OEMs and plant users are summarized below.

• DRYCAP 180D sensor with autocalibration that detects and corrects dry-end drift during normal operation.
• Typical dew point measurement range from −70 to +60 °C (−94 to +140 °F) Td/f.
• Accuracy of ±2 °C Td/f in air or N2 within the specified conditions, and water concentration from 10 to 40 000 ppm.
• Fast response: 5 s to 63 % when the gas becomes wetter (−70 to −20 °C step), typical, at the stated test conditions.
• Sensor that tolerates full condensation, oil vapor and particulate contamination without loss of performance.
• Analog current or voltage output together with RS-485 Modbus RTU for PLC and BMS integration.
• Built-in LED alarm for exceeded dew point, configurable through Vaisala Insight software.
• Compact AISI 316L housing, IP66 rating and four thread options for direct installation up to 50 bar absolute.

Industrial Applications

The most common duty for the Vaisala DMT143 is monitoring the outlet of refrigerant and desiccant compressed air dryers. In Oman this includes instrument-air packages at oil and gas facilities, utility-air systems at power and desalination plants, and the compressor houses of manufacturing sites in the Sohar and Salalah free zones. Plastic injection and extrusion lines use the Vaisala DMT143 inside resin dryers, where too much moisture in the granulate leads directly to surface defects. Because the transmitter is light and small, it also suits OEM machinery such as nitrogen generators, small gas-drying skids and laboratory gas systems that handle air, nitrogen, hydrogen, argon, helium or oxygen, as listed by the manufacturer.

An important limitation should be stated clearly: according to the datasheet the Vaisala DMT143 is not certified for use in hazardous areas with potentially explosive atmospheres. For a classified zone, an intrinsically safe transmitter such as the Michell Easidew EA2 dew point transmitter is the correct choice, while the Vaisala DMT152 dew point transmitter is the Vaisala option intended for very dry gas applications and a CS Instruments FA 510/515 dew point sensor is another option for compressed-air audits. Seven Star LLC supplies these alternatives side by side, so engineers in Muscat and across the GCC can compare them against the actual process conditions before ordering.

Technical Specifications

The following data for the Vaisala DMT143 is taken from the Vaisala datasheet B211207EN-L. Always confirm the final ordering code before purchase.

Installation and Ordering Notes for the Vaisala DMT143

As general engineering guidance, a dew point transmitter gives the most meaningful reading when it sees a small, steady flow of the actual process gas, so many users install it in a sampling cell rather than directly in a dead leg. Vaisala lists several sampling cells for this purpose, including the basic DMT242SC, versions with Swagelok male or VCR connectors, a cell with quick connector and leak screw, and the DMCOILSP cooling and venting coil for hot gas. A mounting bracket, a USB cable for PC connection and loop-powered external displays, with or without relays, are also available as accessories. When ordering the Vaisala DMT143, specify the thread, output type, alarm setting and any accessories so that the transmitter arrives ready for the panel.

How to Order

To request a formal quotation for the Vaisala DMT143, send the required thread, output and alarm option to the Seven Star LLC instrumentation team. We provide engineering support in Muscat, can share the manufacturer datasheet for your technical file, and help match the transmitter to compressed-air, dryer and OEM projects throughout Oman and the GCC.