Rosemount 644 Temperature Transmitter

Fits temperature loops that need a compact head-, field-, or rail-mount transmitter with universal RTD / thermocouple / mV / ohm inputs and HART, FOUNDATION Fieldbus, or PROFIBUS PA output — sensor ordered separately.

Key advantages

Three mount styles — DIN A head, field, or rail mount on one family.
Universal input — Pt100 −200…+850 °C plus RTD / TC / mV / ohm; dual sensor on HART.
Protocol choice — 4–20 mA/HART, FOUNDATION Fieldbus, or PROFIBUS PA.
Pt100 ±0.1 °C — Digital accuracy ±0.1 °C (HART std); enhanced option; FF/PA typical ±0.15 °C class.
SIL 3 capable — IEC 61508 with regional Ex options by order code.

Typical applications

Head-mount temperature transmitters in DIN connection heads.
Rail- or field-mount temperature loops sharing spare parts with 644 family.
Plants mixing HART, FOUNDATION Fieldbus, and PROFIBUS PA temperature points.

Selection guide

Input / range — Pt100 (IEC 751) −200…+850 °C; universal RTD, thermocouple, mV, ohms; single or dual sensor on HART.
Accuracy — Pt100 digital accuracy ±0.1 °C (HART standard); enhanced option; ±0.15 °C typical for FF/PA per family notes.
Output / protocol — 4–20 mA/HART (Rev 5/7); FOUNDATION Fieldbus; PROFIBUS PA.
Supply — 12.0–42.4 Vdc (HART); 9.0–32.0 Vdc (FOUNDATION Fieldbus / PROFIBUS PA).
Mount / housing — DIN A head mount, field mount, or rail mount; aluminum or SST enclosure options.
IP / ambient — Type 4X, IP66, and IP68 (available enclosures); ambient with/without LCD −40…+85 °C (see PDS mount tables).
Display — LCD or enhanced LOI display options.
Area classification — ATEX/IECEx flameproof, IS, Type n, dust options. SIL 3 capable (IEC 61508), ATEX, IECEx, FM, CSA, CE.

Common mistakes

Treating this as a complete probe assembly — the sensor is ordered separately.
Mixing Fieldbus/PROFIBUS supply limits (9.0–32.0 Vdc) with a 4–20 mA HART loop design (12.0–42.4 Vdc).
Assuming dual-sensor capability on every protocol — dual sensor is listed on HART; confirm FF/PA model codes.
Ordering head-mount when the install needs field- or rail-mount housing — mount style is a model-code choice.
Claiming SIL or Ex coverage without the matching order codes on the quote.

When to RFQ / what to tell us

Mount style (head / field / rail), sensor type, single vs dual, and Pt100 accuracy need.
Protocol (HART / FF / PA) and available supply voltage.
Housing material, display, IP/ambient, and required area/SIL marks.
Quantity, ship-to; whether a matching sensor/thermowell is needed.

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Specs

Spec	Value
SKU	25159
Brand	Rosemount
Model	644
Product type	transmitter
Measuring range	Pt100 (IEC 751) input −200…+850 °C; universal RTD / thermocouple / mV / ohm (single or dual sensor on HART)
Sensor type	Universal: RTD (Pt100/Pt200/Pt500/Pt1000 etc.), thermocouple, mV, ohms
Accuracy	Pt100 digital accuracy ±0.1 °C (HART standard); enhanced option available; ±0.15 °C typical for FF/PA per family notes
Output signal	4–20 mA/HART (Rev 5/7); FOUNDATION Fieldbus; PROFIBUS PA
Supply voltage	12.0–42.4 Vdc (HART); 9.0–32.0 Vdc (FOUNDATION Fieldbus / PROFIBUS PA)
Electrical connection	Depends on enclosure (DIN head / field mount conduit entries)
Housing material	Head mount / field mount / rail mount enclosures (aluminum or SST options)
IP rating	Type 4X, IP66, and IP68 (available enclosures)
Ambient temperature	With LCD −40…+85 °C; without LCD −40…+85 °C (see PDS ambient table for mount variants)
Head type	DIN A head mount, field mount, or rail mount
Wiring	2-wire
Communication	HART; FOUNDATION Fieldbus; PROFIBUS PA
Display	LCD or enhanced LOI display options
Approvals	SIL 3 capable (IEC 61508); ATEX; IECEx; FM; CSA; CE
Hazardous area	ATEX/IECEx flameproof, IS, Type n, dust options (order codes E1/I1/N1/E7/I7 etc.)
Mounting	Head mount, field mount, or rail mount
Notes	Transmitter only — processconnection and sheathmaterial blank (sensor ordered separately).

Documents

Rosemount 644 datasheet (PDF)

FAQ

Q: Head, field, or rail mount — which 644 do I need? A: Match the installation. Head mount fits a DIN A connection head; field mount is a stand-alone enclosure; rail mount sits on a DIN rail. IP Type 4X / IP66 / IP68 applies to available enclosures — state mount style in the RFQ.

Q: Does the 644 include a sensor or thermowell? A: No. This SKU is the transmitter only. Process connection and sheath are blank by design — order the RTD/TC separately and list stem / sheath / connection in the RFQ.

Q: Which approvals can I claim on the nameplate? A: Only those on the datasheet and ordered codes: SIL 3 capable (IEC 61508), ATEX, IECEx, FM, CSA, CE. Hazardous-area protection type is selected by order code (E1/I1/N1/E7/I7 etc.). Compatible with systems using Rosemount 644 if you need a drop-in check — we do not claim authorized-dealer status.