Siemens SITRANS TH320 HART Head-Mounted Temperature Transmitter

Overview of the Siemens SITRANS TH320

The Siemens SITRANS TH320 is a two-wire head-mounted temperature transmitter for the 4–20 mA loop, available with and without HART communication. It is installed in the connection head of the temperature sensor, fits type B heads or larger, and offers a universal input that accepts virtually any type of temperature sensor: resistance thermometers in 2-, 3- or 4-wire connection, thermocouples, linear resistance, potentiometers and DC voltage sources. The HART version uses HART 7, and functional safety to SIL2/3 according to IEC 61508 is available as an order option.

Seven Star LLC supplies the Siemens SITRANS TH320 to plant operators, EPC contractors and panel builders across the Sultanate of Oman and the GCC, with engineering support in Muscat. The device is a single-input transmitter; for applications that need two sensor inputs, Siemens offers the TH420 in the same housing, and Seven Star LLC can advise on the right choice for each measuring point.

Operating Principle of the Siemens SITRANS TH320

Inside the Siemens SITRANS TH320, an analog-to-digital converter with 24-bit signal dynamics digitises the sensor signal, a primary microcontroller linearises and processes it, and a secondary microcontroller on the other side of the galvanic isolation drives an 18-bit digital-to-analog converter that produces the load-independent 4–20 mA output. In the HART version the digital HART signal is superimposed on the current, so the loop carries both the temperature-linear analog value and diagnostic data. Isolation between input and output is tested at 2.5 kV AC.

After power-up the transmitter starts within 2.75 s and outputs a temperature-linear signal with a green diagnostics LED. External faults such as a sensor short circuit or wire break make the LED flash red, and a permanent red light indicates an internal device error. Fault currents follow NAMUR NE 43 with upscale above 21 mA and downscale below 3.6 mA, response time is 55 ms or less on the current output, and long-term stability is better than ±0.05 % of span per year and ±0.18 % over five years.

Engineering Design of the Siemens SITRANS TH320

The transmitter weighs only 50 g, the enclosure is potted to IP68, and a centre hole and flexible mounting allow the preferred mounting method in the head; a rail adapter is available for cabinet mounting. Test terminals let an ammeter be connected to check the output current without opening the loop. Supply voltage is 7.5 to 48 V DC for non-Ex installations and 7.5 to 30 V DC for intrinsically safe versions, all inputs and outputs are protected against reversed polarity, and write protection is set by jumper or software.

Configuration of the Siemens SITRANS TH320 with HART is carried out with a handheld communicator or with a HART modem and SIMATIC PDM, while the non-HART version is set up from a PC using the SIPROM T software and a USB modem. Settings are stored in non-volatile EEPROM. Expanded diagnostics include input monitoring for wire break and short circuit, self-monitoring, a slave pointer for minimum and maximum values and an operating hours counter.

Key Features of the Siemens SITRANS TH320

The following points from the Siemens documentation describe the strengths of the Siemens SITRANS TH320:

• Universal input for Pt, Ni and Cu RTDs, thermocouple types B, E, J, K, L, N, R, S, T, U, W3 and W5, resistance up to 100 kΩ, potentiometers and voltage from –100 to 1700 mV.
• Pt100 to IEC 60751 from –200 to +850 °C with a minimum span of 10 °C, and Callendar-Van Dusen sensor matching.
• Two-wire 4–20 mA output with HART 7, update time of 10 ms and programmable damping from 0 to 60 s.
• Galvanic isolation of 2.5 kV AC, polarity protection on all terminals and EMC to EN 61326 and NAMUR NE 21.
• Green/red diagnostics LED and test terminals for checking the loop current without interruption.
• Ambient temperature from –50 to +85 °C and vibration resistance of 4 g from 25 to 100 Hz.
• Intrinsic safety Ex ia/ib/ic and Ex ec/nA approvals under ATEX and IECEx, plus CSA and FM for North America.
• SIL2/3 functional safety to IEC 61508 with order option C20.

Industrial Applications of the Siemens SITRANS TH320

The Siemens SITRANS TH320 is used wherever a temperature sensor needs a robust, compact transmitter in its head: pipelines, storage tanks, heat exchangers, pumps and compressors, boilers and furnaces, HVAC and utility systems, and safety loops when the SIL option is ordered. In Oman these duties appear in oil and gas production stations, refinery and petrochemical units in Sohar, gas processing and LNG facilities, power and desalination plants, and food, pharmaceutical and water utilities where thermowell assemblies are standardised on one transmitter type.

Seven Star LLC supplies the transmitter loose for retrofits or as part of complete sensor assemblies. Engineers can combine it with the Siemens SITRANS TS500 temperature sensor, choose the SITRANS TR200 for DIN rail mounting in the cabinet, or pair it with the SITRANS P320 pressure transmitter on the same skid.

Technical Specifications of the Siemens SITRANS TH320

Key data of the Siemens SITRANS TH320 HART version from the Siemens technical data are summarised below.

How to Order

To order the Siemens SITRANS TH320, send Seven Star LLC the sensor type and wiring, measuring range, HART or non-HART version, hazardous area approval and any SIL requirement, and our instrumentation division will return a formal quotation with factory configuration and delivery timing. The Siemens operating instructions can be downloaded from this page. Seven Star LLC is a trusted supplier of Siemens process instruments in Oman and the GCC, with engineering support in Muscat for configuration and commissioning.