RESISTANCE TEMPERATURE DETECTORS RTDs

The temperature ranges detectable by RTDs are listed in Table 3.169. They are available in a variety of materials, including platinum, which is used for high accuracy, and gold/silver, used on cryogenic temperature applications. The measurement errors are according to classes class A—0.03°C (0.06°F) or 0.01% FS class B—0.12% FS total errors 0.15% of span for platinum, 0.25% of span for nickel. 

In 1821, Sir Humphrey Davy discovered that the resistivity of metals depends on their temperature. The application of this property using platinum was first described by Sir William Siemens. When, in renewable energy or any other processes, accurate measurements are needed RTDs tend to be the first choice. 

RTDs are constructed of a resistive material with leads attached and placed into a protective sheath. Platinum resistance thermometers are the international standard for temperature measurements between the triple point of H2 at 13.81 K (24.86°R) and the freezing point of antimony at 630.75°C (1,167.35°F). The RTD elements include platinum, nickel of various purities, 70% nickel/30% iron (Balco), and copper, listed in order of decreasing temperature range. Their features and relative performance characteristics in comparison with other sensors are tabulated in Table 3.169. 

To eliminate the errors caused by lead wire resistance changes, it is recommended to use transmitters that accept 4-wire RTD inputs as a standard feature. In order to eliminate errors by self-heating, the measuring current should be minimized. For platinum elements, it should not exceed 250 pA. The best installation practice is to place all electronics directly on top of the thermowell and thereby eliminate lead wire and noise effects. If this cannot be done, the lead wires should be twisted and shielded the wires should also not be stressed, strained, or made to go through steep gradients. The 

Evaluation Criteria Platinum RTD 100 n Wire Wound and Thin Film Platinum RTD 1,000 n Thin Film Nickel RTD 1,000 n Wire Wound Balco RTD 2,000 n Wire Wound Thermistor Thermocouple Semi- Conductor Devices 

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HT motors must have a minimum six numbers of resistance temperature detectors (RTDs) (See section 12.8). 

Embedded temperature detectors are resistance temperature detectors (RTDs) or resistance thermometers or thermocouples, built within the machine during manufacture at points that are not accessible when the machine has been assembled. This method is generally employed for the likely hot spots of a machine such as the slot portion and the overhangs of the stator windings. 

This is a later introduction in the sensing of temperature compared to the more conventional types of temperature devices available in an embedded temperature detector (ETD), such as a thermocouple or a resistance temperature detector (RTD) described below. Thermistors can be one of the following types ... 

Verifying temperature is the second most important aspect of any compressor operation. As with pressure, the basic form of measurement is a simple temperature gauge. The construction of the gauges is quite varied, ranging from a bimetallic device to the filled systems. When transmis sion is involved, the sensor becomes quite simple, taking the form v)l a thermocouple or a resistance temperature detector (RTD). The monitor does the translation from the native signal to a temperature readout ()r signal proportional to temperature. 

Metal Oxide-Polymer Thermistors. The variation of electrical properties with temperature heretofore described can be used to tremendous advantage. These so-called thermoelectric effects are commonly used in the operation of electronic temperature measuring devices such as thermocouples, thermistors, and resistance-temperature detectors (RTDs). A thermocouple consists of two dissimilar metals joined at one end. As one end of the thermocouple is heated or cooled, electrons diffuse toward... 

The Resistance Temperature Detector (RTD) or Resistance Thermometer The variation of resistance with temperature 0 for metals can be expressed by ... 

Resistance Temperature Detector (RTD) Type Normal Operating Range (K.) Accuracy (K) Comments... 

Resistance temperature detector (RTD) Venturi Elastic element Chain gauge Mass spectrometry (MS)... 

Temperature is by far the more frequently measured state variable and is considered in some detail hereafter. Basic temperature measurement in a batch reactor must regard, at least, the reacting mixture and the heat exchange fluid. To this goal, the devices most widely used are thermocouples and resistance temperature detectors (RTD). 

Because temperature is one of the most important parameters of a material, many instruments have been developed to measure it. One type of detector used is the resistance temperature detector (RTD). The RTD is used at many DOE nuclear facilities to measure temperatures of the process or materials being monitored. 

Resistance temperature detectors (RTDs) are summarized below. 

FIGURE 6.15 Schematic drawings (top view) depicting (a) the capture and separation electrode, heater, and resistive temperature detector (RTD) module on the silicon substrate (b) the electrophoresis channel layout on the glass substrate and (c) the assembled device consisting of the glass channel bonded on top of the silicon substrate [95]. Reprinted with permission from Wiley-VCH Verlag. 

Thermocouples are usually not accurate enough for the precise measurement of temperature differences and are not fast enough to detect highspeed variations in temperature. Resistance temperature detectors (RTDs) can detect temperature differences of 5°C (10°F) at a measurement error of 0.02°C ( 0.04°F). If higher-speed response is desired, thermistors or infrared detectors should be considered. 

In the category of electronic thermometers, the thermocouples (TCs), resistance temperature detectors (RTDs), thermistors, integrated circuitry (IC), and radiation thermometers will be discussed in separate subsections. The IC and diode detectors will be discussed in connection with cryogenic thermometry. Their characteristics are shown in Figure 3.161. 

As was shown in Figure 3.159, cryogenic temperatures can be detected by integrated circuit diodes types K, T, and E thermocouples (TCs) class A and B resistance temperature detectors (RTDs) acoustic and ultrasonic thermometers germanium and carbon resistors and paramagnetic salts. As TCs and RTDs will be discussed in separate subsections, here the focus will be on the other sensors. 

Figure 2.1 Thermal behavior of a thermistor [1] and a platinum resistance temperature detector (RTD) [2],...

Temperatures can be measured with thermocouple (T/C) or resistance temperature detector (RTD). RTD provides for stability its variation in temperature is both repeatable and predictable. T/Cs tend to have shorter response time, while RTDs have less drift and are easier to calibrate. RTD provides for stability its variation in temperature is both repeatable and predictable. RTD contains a temperature sensor made from a material such as high purity platinum wire resistance of the wire changes rapidly with temperatures. These sensors are about 60 times more sensitive than thermocouples. 

Temperature detectors embedded in the motor winding give close, accurate indication of motor temperature. Both conventional resistance temperature detectors (RTD) and special thermistors (highly temperature-sensitive nonlinear resistors) are used. With appropriate auxiliaries these devices can indicate or record motor temperature, alarm, and/or shut down the motor. 

The schematic diagram of PSA apparatus was shown in Figure 1. The adsorption beds were made of stainless steel pipe with a length of 100cm, ID of 2.2cm, and wall thickness of O.lTScm. The beds were packed with CMS from the Takeda chemical company. Calibrated three resistance temperature detectors (RTD, Pt lOOQ) were installed at the positions of 10, 50, and 80cm from the feed end in order to measure the temperature variations inside the bed. The two pressure transducers were located at the feed and product ends in order to measure the bed pressure variation. The feed flow rate was... 

Temperature. Prefer resistance temperature detectors, RTD. Prefer narrow span transmitters instead of thermocouples. 

For industrial applications, PRTs are also called resistance temperature detectors (RTDs). For applications in the range from 0 to 300°C, these commercially available RTDs are capable of an accuracy of about 0.05°C, and they can usually maintain their accuracy to within 0.2°C for two or more years. If these RTDs are first annealed before calibration they are capable of maintaining an accuracy of 0.01°C [26]. 

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