Endress+Hauser TMR31 Compact RTD Thermometer

Endress+Hauser TMR31 compact RTD thermometer with 4-20 mA option

The Endress+Hauser TMR31 is a metric compact thermometer built around a Pt100 sensor and, optionally, an integrated 4 to 20 mA transmitter. It replaces the usual combination of a separate probe, a head and a head transmitter with one small stainless steel body that screws directly into a pipe or vessel, which saves space, wiring and installation time. The vibration-proof thin-film element gives a fast response, with t50 of 1 s and t90 of 2 s, and the M12 connector offers IP69K protection as standard. Seven Star LLC supplies the TMR31 in Oman and the GCC as an independent supplier in Muscat.

The same technical information also covers the hygienic TMR35. This page concerns the TMR31 with threaded process connection, with or without a neck.

TMR31 technical specifications

Inside the TMR31: sensor and electronics

The temperature sensor is a Pt100 to IEC 60751 in class A, connected with four wires. In the version with a built-in transmitter, the Pt100 signal is converted to a 4 to 20 mA output with a variable measuring range, and failure information follows NAMUR NE43: linear drop to 3.8 mA, linear rise to 20.5 mA, or a selectable low (3.6 mA or below) or high (21 mA or above) alarm. The permitted loop load follows the formula Rb max = (Ub max − 10 V) / 0.023 A, so check the supply and the load of your loop. The device must be powered by a limited-energy supply when electrical safety to CSA or UL standards is needed.

TMR31 technical data

The Pt100 operating range is −50 to +200 °C; the manufacturer quotes the application range as −50 to +150 °C, or up to +200 °C with a neck. Maximum static pressure is 100 bar at 20 °C. The probe diameter is 4 or 6 mm, immersion length can be up to 600 mm on request, and the material is 1.4404 (316L). The process connection is a thread, with or without a neck, and the sensor is an insert pipe with isolated wires, not flexible. The M12 connection with 4-pin plug avoids wiring errors, and marine approval is listed among the benefits.

Selecting the TMR31

Choose immersion length so that the sensing tip sits in the flow and at least 10 times the tube diameter is immersed in a pipe; for a small bore pipe use an elbow or an inclined mounting. Decide whether you need the 4 to 20 mA electronics or a plain 4-wire Pt100, and the thread type (metric, G or NPT). Note that a compact thermometer is not designed for use in a thermowell; if the line must stay closed during sensor change, choose a modular thermometer with thermowell such as the TM131 or TM151 instead.

Installing and wiring the TMR31

Screw the thermometer into the process connection with a suitable sealing washer or PTFE-based sealant, do not turn it by the housing, and align the M12 connector so the cable hangs downwards in outdoor installations to drain water. Connect through a power supply or barrier of the correct type. Where ambient temperature is high, such as under a pump or near a heat exchanger, make sure the electronics are within their ambient range; use the neck variant to move the electronics away from a hot process.

TMR31 in Oman and GCC plants

The TMR31 suits utility and skid applications: cooling-water supply and return on pumps, heat-exchanger inlets and outlets, lube-oil temperature on compressors, chilled-water in HVAC plants and temperature monitoring on package units. High ambient temperatures and wash-down are handled by the IP69K connection. For hazardous areas, check the document for an Ex version before choosing.

TMR31 compared with the TMR35 and TM series

Information to send with a TMR31 RFQ

• Temperature range and process pressure
• Thread, immersion length and neck
• Pt100 only or with 4 to 20 mA transmitter
• Connector and cable
• Marine or other approval
• Quantity and delivery location

Maintenance, verification and spares for the TMR31

A compact thermometer is replaced as one unit, so spares planning is simple: keep a unit with the same thread, probe length, neck and output on the shelf, and record the order code from the nameplate. Verify the reading periodically against a reference in a dry-block or oil bath, and check the 4 to 20 mA loop with a calibrator. If the signal drifts or goes to the alarm level, check the M12 connector for moisture first.

Site conditions in Oman for the TMR31

Field instruments in Oman are exposed to strong sun, high ambient temperature, wind-blown dust and, on coastal plants, salt in the air. When you specify the TMR31, check the ambient and process temperature limits, the enclosure rating and the wetted and housing materials against the actual installation point, and consider sunshades for transmitters mounted in direct sunlight. Cable entries should be sealed with suitable glands so that dust and moisture cannot enter the housing.

Calibration and verification planning matters as much as selection. Record the range, configuration and tag data of each TMR31 at commissioning, define a check interval that suits the criticality of the loop, and keep the certificates with the plant documentation so that audits and shutdown work can proceed without delay.

Documents and quotation

A copy of the manufacturer technical information for the TMR31 is attached on this page so you can check ranges, connections and ordering codes against your specification. The attached document covers both the TMR31 and the TMR35.

Send the full order code or the process data (fluid, temperature, pressure, line size or tank data, output and approvals) and Seven Star LLC will prepare a quotation and confirm lead time. We are an independent supplier in Muscat and do not represent the manufacturer.