RTDs In Depth

Resistance Temperature Detectors (RTDs) rely on the predictable and repeatable phenomena of the electrical resistance of metals changing with temperature. The most common metals used for temperature sensing are platinum, nickel and copper.

How are RTDs manufactured

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A Wire RTD

RTD’s are manufactured using either wire or film. A Film RTD consists of a thin metal film silk screened onto a ceramic or glassy substrate. These sensors are less accurate than wire RTDs but are relatively inexpensive and available in small sizes.
Wire RTDs consist of a length of fine coiled wire wrapped around a ceramic or glass core. These wire RTDs are generally more accurate & are also the more expensive style of RTDs
RTDs are extremely delicate so they are usually protected by a sheath most commonly stainless steel. The Stainless steel tube diameters can range from 3-15mm and can be made to any desired length.

Types of RTDs

While almost any metal may be used for RTD manufacture, the most common D&N Manufacture are:
Copper (Pt): This low cost metal has a temperature range of -200°C to 260°C
Nickel (Ni): This metal is also low cost but has a limited temperature range of -80°C to 260°C
Nickel- Iron (Ni-Fe): This is still a low cost metal but has an extended temperature range of -200°C to 200°C
Platinum (Pt): High precision metal with a large temperature range of -240°C to 660°C. Platinum is the most common metal used in RTD manufacture.

Tolerance

RTD bulbs come in classes A through to D, each with their own error tolerance. D&N Engineering only use high quality Class A bulbs with a tolerance of +/- 0.15C.

2,3 or 4 wire calibration

RTDs are offered with 2,3 and 4 wire configurations. The best configuration for an application depends on a range of factors and must match the transmitter.
The more wires used generally means higher cost & requires additional space. Accuracy requirements is also a large factor with 2 wire being much less accurate than the 4 wire configuration.
For more information on RTDs read our blog “RTD vs Thermocouple”
D&N Engineering supplies are experts within the field of temperature measurement and our sales team will be happy to help find the perfect measurement solution to your project.