Rosemount 644 Head Mount Temperature Transmitter

Overview

The Rosemount 644 Head Mount Temperature Transmitter is one of the most widely deployed temperature transmitters in the global process industry, trusted for its measurement accuracy, transmitter-sensor matching, and long-term reliability in demanding plant environments. Built to mount directly inside a DIN Form B connection head on a thermowell assembly, the Rosemount 644 accepts RTD, thermocouple, millivolt, and ohms inputs and converts the sensor signal into a stable digital or analog output using HART®, FOUNDATION™ Fieldbus, or PROFIBUS® PA protocols – giving engineers a single transmitter platform that covers nearly every temperature measurement point in a facility.

In Oman and the GCC, Seven Star LLC supplies the Rosemount 644 Head Mount Temperature Transmitter on request with manufacturer documentation and technical backing. Facilities across Muscat, Sohar, and Salalah can source Emerson Rosemount instrumentation through Seven Star LLC, with availability and lead time confirmed at quotation.

Measurement Principle

The Rosemount 644 operates by accepting a resistance or voltage signal from a connected RTD or thermocouple sensor and applying Callendar-Van Dusen constants unique to the matched sensor to correct for individual sensor curve variation, reducing total measurement error to a fraction of what a generic transmitter-sensor pairing would achieve. The transmitter’s onboard diagnostics continuously evaluate sensor health, flagging drift, degradation, or open/short-circuit sensor failure well before the condition affects process control – a critical capability in continuous processes where an undetected temperature excursion can mean a batch loss or a safety event.

Dual-sensor variants of the Rosemount 644 support Hot Backup™ functionality, automatically switching to a secondary sensor if the primary sensor fails, and providing a sensor drift alert that compares both sensor readings in real time. Because the transmitter performs signal conditioning and linearization directly at the measurement point rather than at a remote marshalling cabinet, the resulting 4-20 mA or digital signal is immune to the lead-wire resistance errors, electrical noise pickup, and cable-run signal degradation that plague remote RTD wiring – delivering a clean, drift-free reading regardless of how far the control room sits from the field.

Engineering Design of the Rosemount 644

The Rosemount 644 is a compact, circular electronics module engineered to fit inside a standard DIN Form B connection head, the industry-standard housing style used on the vast majority of thermowell and sensor assemblies worldwide. This form-factor compatibility means the Rosemount 644 can retrofit directly into existing temperature assemblies without requiring a new housing, thermowell, or wiring scheme – a significant advantage during plant upgrades and transmitter replacement programs. The module terminal block accepts 2, 3, or 4-wire RTD connections as well as thermocouple leads, with a dedicated test terminal that allows technicians to simulate or verify the output signal without disconnecting field wiring.

An optional Local Operator Interface (LOI) provides on-site configuration and diagnostic access using magnetic push-buttons operated through the housing glass, allowing range, damping, and alarm settings to be adjusted in the field without opening the enclosure in a hazardous area. The electronics are conformal-coated and rated for continuous operation across an extreme ambient temperature range, and the transmitter is certified for installation in explosion-proof, flameproof, intrinsically safe, and non-incendive hazardous locations, making it suitable for refineries, offshore platforms, gas processing trains, and other Zone 0/1/2 classified areas common throughout Oman’s oil and gas sector.

Key Features

The Rosemount 644 Head Mount Temperature Transmitter combines proven measurement accuracy with a feature set built specifically for demanding industrial temperature applications.

• Transmitter-sensor matching using Callendar-Van Dusen constants reduces total measurement error compared with unmatched sensor-transmitter pairings.
• Hot Backup™ dual-sensor capability automatically transfers to a secondary sensor on primary sensor failure, maintaining continuous measurement without a process interruption.
• Thermocouple degradation diagnostics continuously monitor thermocouple health and warn of impending sensor failure before it affects the loop.
• Minimum and maximum temperature tracking records process excursions for troubleshooting and historical trend analysis.
• Compatible with HART, FOUNDATION Fieldbus, and PROFIBUS PA protocols for seamless integration into existing DCS and asset management systems.
• Fits the standard DIN Form B connection head, enabling drop-in retrofit into existing thermowell assemblies without mechanical modification.
• Optional Local Operator Interface allows field configuration and verification without opening the housing in classified hazardous areas.
• Certified for explosion-proof, flameproof, and intrinsically safe installation across global hazardous-area standards.

Industrial Applications

The Rosemount 644 is deployed across virtually every process industry that requires reliable point temperature measurement, including oil and gas production and refining, petrochemical processing, power generation, food and beverage manufacturing, and life sciences production. Its head-mount, DIN Form B form factor makes it the default choice for retrofitting legacy thermowell installations throughout process trains, tank farms, compressor stations, and utility systems where thousands of individual temperature points must be measured with consistent accuracy and minimal maintenance overhead.

In Oman and the GCC, Seven Star LLC supplies the Rosemount 644 to engineering, procurement, and construction contractors, oilfield service companies, and plant maintenance teams across the Sultanate of Oman and the wider GCC. From the Sohar and Salalah free zones to upstream facilities in the interior and offshore platforms in the Arabian Sea, Seven Star LLC supplies Emerson Rosemount temperature transmitters on request with manufacturer documentation and responsive regional technical support.

Technical Specifications

The table below summarizes the core specifications of the Rosemount 644 Head Mount Temperature Transmitter.

Request a Quote for Rosemount 644

Facilities throughout Oman and the GCC can request a formal quotation for the Rosemount 644 Head Mount Temperature Transmitter directly from Seven Star LLC, with lead time confirmed at quotation, technical datasheet downloads, and full support from our instrumentation division. In Oman and the GCC, Seven Star LLC supplies each unit on request with manufacturer documentation and the local technical support needed to specify critical temperature measurement loops correctly. Contact our sales engineering team today to specify the correct sensor input, housing, and protocol configuration for your application.

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