Strengths & Weaknesses of Temperature sensor

Each type of temperature sensor has particular strengths and weaknesses.

RTD Strengths:

RTD's are commonly used in applications where repeatability and accuracy are important considerations. Properly constructed Platinum RTD's have very repeatable resistance vs. temperature characteristics over time. If a process will be run at a specific temperature, the specific resistance of the RTD at that temperature can be determined in the laboratory and it will not vary significantly over time. RTD's also allow for easier interchangeability since their original variation is much lower than that of thermocouples. For example, a Type K thermocouple used at 400°C has a standard limit of error of ±4°C. A 100-Ohm DIN, Grade B platinum RTD has an interchangeability of ±2.2°C at this same temperature. RTD's also can be used with standard instrumentation cable for connection to display or control equipment where thermocouples must have matching thermocouple wire to obtain an accurate measurement.

RTD Weaknesses:

In the same configuration, you can expect to pay from 2 to 4 times more for an RTD than for a base metal thermocouple. RTD's are more expensive than thermocouples because there is more construction required to make the RTD including manufacture of the sensing element, the hooking up of extension wires and assembly of the sensor. RTD's do not do as well as thermocouples in high vibration and mechanical shock environments due to the construction of the sensing element. RTD's are also limited in temperature to approximately 650°C where thermocouples can be used as high as 1700°C.

Thermocouple Strengths:

Thermocouples can be used to temperatures as high as 1700°C, generally cost less than RTD's and they can be made smaller in size (down to approximately .020'' dia) to allow for faster response to temperature. Thermocouples are also more durable than RTD's and can therefore be used in high vibration and shock applications.

Thermocouple Weaknesses:

Thermocouples are less stable than RTD's when exposed to moderate or high temperature conditions. In critical applications, thermocouples should be removed and tested under controlled conditions in order to verify performance. Thermocouple extension wire must be used in hooking up thermocouple sensors to thermocouple instrument or control equipment. Use of instrumentation wire (plated copper) will result in errors when ambient temperatures change.