If you are not sure which wires are connected to which side of the resistive element, you can use a digital multimeter (DMM) to measure the resistance between the leads. The red wire is the excitation wire and the black or white wires are ground wires. The resistance/temperature curve for a 100 Ω platinum RTD, commonly referred to as Pt100, is shown in Figure 2.Īll RTDs usually come in a red and black or red and white wire-color combination. The relationship between resistance and temperature is nearly linear and follows this equation:Ī, b, and c = constants used to scale the RTD
Typical nominal resistance values for platinum thin-film RTDs include 1 Ω. RTDs are commonly categorized by their nominal resistance at 0 ☌. RTDs are also characterized by a slow response time and low sensitivity, and, because they require current excitation, they can be prone to self-heating. However, they are generally more expensive than alternatives because of the careful construction and use of platinum. Popular because of their stability, RTDs exhibit the most linear signal with respect to temperature of any electronic temperature sensor. To protect the RTD, a metal sheath encloses the RTD element and the lead wires connected to it. Thin-film elements are cheaper and more widely available because they can achieve higher nominal resistances with less platinum.
A more common configuration is the thin-film element, which consists of a very thin layer of metal laid out on a plastic or ceramic substrate. Wire-wound RTDs are created by winding a thin wire into a coil. RTDs are constructed using one of two different manufacturing configurations. Typical elements used for RTDs include nickel (Ni) and copper (Cu), but platinum (Pt) is by far the most common because of its wide temperature range, accuracy, and stability. It is observed that when glass is heated, it cracks while metal does not.RTDs operate on the principle of changes in electrical resistance of pure metals and are characterized by a linear positive change in resistance with temperature. Thus, air is a very good insulator of heat. Liquids like water are poor conductors and gases are very poor conductors of heat. Some of the examples of heat or thermal insulators are plastic, wood, paper, cloth, thermocol, rubber, etc. Substances that do not conduct heat very welfare called bad conductors or poor conductors or insulators of heat. Among metals, silver metal is the best conductor of heat, next is copper and lowest is lead. Though all the metals are good conductors of heat, some metals are better conductors of heat than the others. All the metals such as silver, copper, aluminum, iron, mercury and metal alloys such as brass, steel and stainless steel are good conductors of heat. Passage - 1 Substances that conduct heat very well are called good conductors of heat or thermal conductors. DIRECTIONS: Read the passage given below an answer the questions that follow.
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