2 Wire, 3 Wire, and 4 Wire RTD Sensor Connections

Industrial temperature
transmitters (courtesy of
Siemens)

Industrial temperature transmitters are devices that measure the temperature of a process and provide a measurable output over some desired temperature range. Industrial temperature transmitters primarily use either of two popular temperature sensors - the thermocouple or the RTD (resistance temperature detector). The RTD changes resistance as process temperature changes, while a thermocouple provides a changing micro-voltage with process temperature change. RTDs are inherently more accurate, but require excitation voltage. There are three style RTD's - 2-wire, 3-wire, and 4-wire.

Proper connections for all three types of RTD sensor to a user- configurable transmitter are shown in the following illustrations:

Proper wiring of RTDs

It is critically important to note that the common connections shown by the symbols for 3- and 4-wire RTD sensors represent junction points at the sensor; not terminals jumpered by the technician at the time of installation, and not internal jumpers inside the transmitter. The whole purpose of having 3-wire and 4-wire RTD circuits is to eliminate errors due to voltage drop along the current-carrying wires, and this can only be realized if the “sensing” wire(s) extend out to the RTD itself and connect there. If the transmitter’s sensing terminal(s) are only jumpered to a current- carrying terminal, the transmitter will sense voltage dropped by the RTD plus voltage dropped by the current-carrying wire(s), leading to falsely high temperature indications.

Click here for more information on industrial RTDs and temperature transmitters.

For more information about any temperature measuring application, contact:
Ives Equipment
www.ivesequipment.com
(877) 768-1600

Some of above content taken from Lessons In Industrial Instrumentation by Tony R. Kuphaldt – under the terms and conditions of the Creative Commons Attribution 4.0 International Public License.

A Specialty Temperature Sensor Specifically for Improving Heat Tracing Applications

Heat Tracing RTD (courtesy of
Applied Sensor Technologies)

A temperature sensor is key to any heat tracing application as it provides temperature feedback about the pipe temperature, which in turn, is used turn on or off the heating system (electric pipe tracing or steam control valve).

The temperature sensor is critical for both categories of heat tracing - process temperature maintenance and freeze protection.  Failure to maintain process temperature in a pipe or vessel could significantly effect product quality, or cause failure of ancillary equipment such as pumps, valves, and compressors. Properly protecting against freezing keeps pipes from bursting or product from blocking the flow. For both situations, product maintenance and freeze protection, accurate and reliable temperature sensing is critical.

There’s a new and very innovative line of RTD temperature assemblies specifically designed for heat tracing applications. The unique, replaceable element concept can save customers both time and money, plus increase overall system reliability and up-time.

A major refining company determined that they save over $1,000 in labor each time they have to replace a sensor and have reduced their repair time from two days to less than one hour.

The design consists of a terminal head and right-angle shaped outer sheath, with a curved weld-pad at the end. The replaceable RTD element assembly is contained in the outer tube and, when installed, presses against the pipe. Heat transfer is excellent and heat conduction away from the element is minimal. Should the element ever need to be replaced, it's a five-minute job to open the terminal head, unwire the sensor, slide it out and slide a new one in.

For more information, contact:

Ives Equipment
(877) 768-1600

www.ivesequipment.com