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| 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.
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| 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
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.
