Detector Thermal detectors

Detectors for IR radiation fall into two classes thermal detectors and photon-sensitive detectors. Thermal detectors include thermocouples, bolometers, thermistors, and... 

Fire and Smoke Detection Fire detection systems and alarms should be considered in hazardous locations. These include gas, thermal, smoke detectors, thermal detectors, as well as IR/UV flame scanners... 

Detectors for IR radiation fall into two classes thermal detectors and photon-sensitive detectors. Thermal detectors include thermocouples, bolometers, thermistors, and pyroelectric devices. Thermal detectors tend to be slower in response than photon-sensitive saniconduc-tors. The most common types of detectors used in dispersive IR spectroscopy were bolometers, thermocouples, and thermistors, but faster detectors are required for FTIR. FTIR relies on pyroelectric and photon-sensitive semiconducting detectors. Table 4.5 summarizes the wavenumber ranges covered by commonly used detectors. 

Ultraviolet and Infrared Radiation Monitoring Devices. A variety of instruments are commonly used to measure ultraviolet and infrared radiation.They are classified according to the type of detector used, which is generally one of two types thermal detectors or photoelectric detectors. Thermal detectors are those in which the absorbed radiation is degraded to heat and subsequently converted to an electric signal by changing the electric resistance of a filament. Photoelectric detectors are based on the principle that the absorbed photons eject electrons from a material. Most of these instruments are precalibrated by the manufacturer, but should be routinely checked prior to field use. 

We mentioned that Herschel s detector was a thermometer - the first thermal detector. Thermal detectors respond to the power falling on the detector and they are still used - though they are more sensitive than Hershel s thermometer. However, another detector type is now very important. Called photon detectors, these respond not to the power falling on the detector but on the rate of arrival of photons - discrete packets of energy. We will discuss photons in Chapter 2, and the two detector types in Chapters 3 and 4. 

By far the most used detector is the thermal conductivity detector (TCD). Detectors like the TCD are called bulk-property detectors, in that the response is to a property of the overall material flowing through the detector, in this case the thermal conductivity of the stream, which includes the carrier gas (mobile phase) and any material that may be traveling with it. The principle behind a TCD is that a hot body loses heat at a rate that depends on the... 

For most points requiring temperature monitoring, either thermocouples or resistive thermal detectors (RTD s) can be used. Each type of temperature transducer has its own advantages and disadvantages, and both should be considered when temperature is to be measured. Since there is considerable confusion in this area, a short discussion of the two types of transducers is necessaiy. 

ELCD, HECD Electrolytic conductivity (Hall) detector Thermal generation of inorganic ions... 

Nonspectroscopic detection schemes are generally based on ionisation (e.g. FID, PID, ECD, MS) or thermal, chemical and (electro)chemical effects (e.g. CL, FPD, ECD, coulometry, colorimetry). Thermal detectors generally exhibit a poor selectivity. Electrochemical detectors are based on the principles of capacitance (dielectric constant detector), resistance (conductivity detector), voltage (potentiometric detector) and current (coulometric, polarographic and amperometric detectors) [35]. 

X-ray diffraction (XRD) patterns for the materials were recorded on a X-ray diffractometer using nickel-filtered CuKa (0.154 nm) radiation and a liquid nitrogen-cooled germanium solid-state detector. Thermal stability of the materials was performed using a thermogravimetric analyser. The acidity of calcined samples were determined... 

IR detectors convert (thermal) radiation energy into electrical signals. Two classes of such detectors exist thermal detectors and quantum detectors. 

The measurement of the cosmic microwave background. Far infrared astronomers were the first to develop thermal detectors. Some of the resulting technologies, such as neutron transmutation doping (NTD) [3], have been transferred to particle detection sensors and have allowed many groups (e.g., ref. [4-11] to make rapid progress). 

An extremely simplified scheme of a calorimeter (composite thermal detector) is shown in Fig. 15.6. The temperature of an absorber A (TA) is measured by a thermometer T. A thermal conductance G forms a thermal link with the heat sink B at the temperature Ts. In the ideal adiabatic situation (G = 0), an absorption of an energy AE produces an absorber temperature increase ... 

Horikawa [126] has adapted a thermal detector for the determination of formic, acetic, and propionic acids by liquid chromatography. 

Thermal or heat detectors respond to the energy emission from a fire in the form or heat. The normal means by which the detector is activated is by convention currents of heated air or combustion products or by radiation effects. Because this means of activation takes some time to achieve thermal detectors are slower to respond to a fire when compared to some other detection devices. 

Fig. 21.2. Gas-solid chromatogram of vapor sample from bulging drum (column 5-ft X 1/8 in o.d. aluminum packed with molecular sieve 5A 60-80 mesh column temperature ambient 25°C to 28°C detector thermal conductivity at 80°C carrier gas Ar at 15cm3/min. (Reprinted/redrawn with permission from Analyt. Chem., 56, 603A (1984). Copyright 1984 American Chemical Society.)...

IR spectrometers have the same components as UY/visible, except the materials need to be specially selected for their transmission properties in the IR (e.g., NaCl prisms for the monochromators). The radiation source is simply an inert substance heated to about 1500 °C (e.g., the Nernst glower, which uses a cylinder composed of rare earth oxides). Detection is usually by a thermal detector, such as a simple thermocouple, or some similar device. Two-beam system instruments often work on the null principle, in which the power of the reference beam is mechanically attenuated by the gradual insertion of a wedge-shaped absorber inserted into the beam, until it matches the power in the sample beam. In a simple ( flatbed ) system with a chart recorder, the movement of the mechanical attenuator is directly linked to the chart recorder. The output spectrum is essentially a record of the degree of... 

Detection of the middle and far range of infrared radiation requires thermal detectors, the simplest of which is a thermocouple, in which the change in temperature at one junction of the thermocouple results in a small voltage being produced. Although simple in design, thermocouples lack sensitivity. Bolometers are more sensitive and are based on the fact that as the temperature of a conductor... 

Thermal detector Senses when temperatures exceed a set threshold (fixed temperature detector) or when the rate of change of temperature increases over a fixed time period (rate-of-rise detector). 

Multi-sensor detector Is a combination of photoelectric and thermal detectors. The photoelectric sensor serves to detect smoldering fires, while the thermal detector senses the heat given off from fast-burning/flaming fires. 

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