RTDs are made of metals of a special material (usually platinum) whose electrical resistance changes with temperature. Electrical resistance generally increases with increasing temperature, in which case the equipment has a positive temperature coefficient. Determines the sensitivity of RTD.
RTD sensor element material:
The thermal resistance properties of the RTD sensor element vary depending on the metal or alloy it is made of. The metal or alloy used as the RTD sensor must have the following characteristics:
* Sensor element resistance The RTD should be relatively high so that it can be easily measured.
* The sensor element must have physical strength.
* Has a stability (non-melting and not freezing) in the measuring temperature range.
* For a certain change in temperature, the change in resistance of the sensor element must be large enough to be easily measurable.
Temperature coefficient (Temperature Coefficient)
The temperature coefficient indicates the amount of change in the resistance of a metal in exchange for a change in temperature and its unit is ohm / c. The larger the temperature coefficient, the greater the change in resistance for a specific change in temperature. The overall temperature coefficient expresses the sensitivity of the equipment. RTDs are completely linear, although the temperature coefficient varies over the operating range. For example, the average platinum temperature coefficient ranges from 0 ° C to 150 ° C. C is 0.00385Ohm / c and varies in the range of about 0.2%.
The three most commonly used resistance metals for RTD are:
RTD elements are made of platinum, the most common type of RTD used in process industries. Platinum elements have high accuracy, repeatability and resistance to temperature change. In addition, platinum RTD elements are highly linear in the operating temperature range.
There are two main types of platinum RTDs, called PT1000 and
In this case, PT stands for Platinum for metal heatsink, but the resistance is 1000 ohms at 0 ° C.
These sensors are generally thin-film type.
There are also Chance Platinum RTDs with 200 and 500 ohm resistors, but they are expensive and less commonly used.
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