Temperature measurement, sensors

All parts of the plant, such as venting hlter, pressure-measuring sensors, temperature-measuring sensors, and their lead-throughs, within the sterilization area are also sterilized. 

Protocol 1 The reaction was performed in a CEM Discover 1-300 W system equipped with a built-in pressure measurement sensor and a vertically focused IR temperature measurement sensor using the mode Discover Standard. A solution of 5,5-dimethyl-2-diazocyclohexan-1,3-dione (1, 115 mg, 0.69 mmol), benzaldehyde (70 pL, 0.69 mmol), and fR)-phenylethylamine (88 p,L, 0.69 mmol) in 2mL of anhydrous toluene (0.35 M) under an argon atmosphere in a 10-mL sealed borosilicate tubular reaction vessel containing a Teflon-coated magnetic stirring bar was irradiated at 140 °C for 5 minutes after a ramp-up time of 2 minutes (total irradiation time = 7 minutes). The resulting reaction mixture was cooled to 50 °C by air flow, concentrated, and directly purified by flash chromatography on silica gel eluted with EtOAc/petrol ether to afford the... 

Protocol 3 The reaction was performed in a CEM Discover 1-300 W system equipped with a built-in pressure measurement sensor and a vertically focused IR temperature measurement sensor. A solution of 2-diazocyclohexan-... 

Protocol 4 The reaction was performed in a CEM Discover 1-300 W system equipped with a built-in pressure measurement sensor and a vertically focused IR temperature measurement sensor using the mode Discover Standard. A solution of 5,5-dimethyl-2-diazocyclohexan-l,3-dione (1, 126 mg, 0.76 mmol), cinnamaldehyde (95pJL, 0.76 mmol), and benzylamine (83 pJL, 0.76 mmol) in 2mL... 

Process-variable feedback for the controller is achieved by one of two methods. The process variable can (I) be measured and transmitted to the controller by using a separate measurement transmitter with a 0.2-I.0-bar (3-15-psi pneumatic output, or (2) be sensed directly by the controller, which contains the measurement sensor within its enclosure. Controllers with integral sensing elements are available that sense pressure, differential pressure, temperature, and level. Some controller designs have the set point adjustment knob in the controller, making set point adjustment a local and manual operation. Other types receive a set point from a remotely located pneumatic source, such as a manual air set regulator or another controller, to achieve set point adjustment. There are versions of the pneumatic controller that support the useful one-, two-, and three-mode combinations of proportional, integral, and derivative actions. Other options include auto/manual transfer stations, antireset windup circuitry, on/off control, and process-variable and set point indicators. 

A regulator is a compact device that maintains the process variable at a specific value in spite of disturbances in load flow. It combines the functions of the measurement sensor, controher, and final control element into one self-contained device. Regulators are available to control pressure, differential pressure, temperature, flow, hquid level, and other basic process variables. They are used to control the differential across a filter press, heat exchanger, or orifice plate. Regulators are used for monitoring pressure variables for redundancy, flow check, and liquid surge relief. 

Turbomaehinery operating pressures, temperatures, and speeds are very important parameters. Obtaining aeeurate pressures and temperatures will depend not only on the type and quality of the transdueers seleeted, but also on their loeation in the gas path of the maehine. These faetors should be earefully evaluated. The aeeuraey of pressure and temperature measurements required will depend on the analysis and diagnosties that need to be performed. Table 19-2 presents some eriteria for seleetion of aerothermai instrumentation of pressure and temperature sensors for measurement of eompressor effieieney. Note that the pereentage aeeuraey requirements are more eritieal for temperature sensors than pressure sensors. The requirements are also dependent on the eompressor pressure ratio. 

The sensor is the element of an instrument directly influenced by the measured quantity. In temperature measurement the thermal mass (capacity) of the sensor usually determines the meter s dynamics. The same applies to thermal anemometers. In IR analyzers used for concentration measurement, the volume of the flow cell and the sample flow rate are the critical factors. Some instruments, like sound-level meters, respond very fast, and follow the pressure changes up to several kHz. 

For example, a temperature-measuring device, having its sensor placed in a protecting rube, is a system of second order. For such a system no single rime constant exists in the same way as a first-order system. The behavior of such a system is often given by a response time. Another concept is to give the apparent time constant t, which can be constructed by placing a line in the inflection point of the step response curve see Fig. 12.14. 

Contact temperature measurement is based on a sensor or a probe, which is in direct contact with the fluid or material. A basic factor to understand is that in using the contact measurement principle, the result of measurement is the temperature of the measurement sensor itself. In unfavorable situations, the sensor temperature is not necessarily close to the fluid or material temperature, which is the point of interest. The reason for this is that the sensor usually has a heat transfer connection with other surrounding temperatures by radiation, conduction, or convection, or a combination of these. As a consequence, heat flow to or from the sensor will influence the sensor temperature. The sensor temperature will stabilize to a level different from the measured medium temperature. The expressions radiation error and conduction error relate to the mode of heat transfer involved. Careful planning of the measurements will assist in avoiding these errors. 

Intelligent transmitters have two major components (1) a sensor module which comprises the process connections and sensor assembly, and (2) a two-compartment electronics housing with a terminal block and an electronics module that contains signal conditioning circuits and a microprocessor. Figure 6.9 illustrates how the primary output signal is compensated for errors caused in pressure-sensor temperature. An internal sensor measures the temperature of the pressure sensor. This measurement is fed into the microprocessor where the primary measurement signal is appropriately corrected. This temperature measurement is also transmitted to receivers over the communications network. 

Temperature measurements, (a) Platinum wire sensor measurements and (b) silicon carbide filaments. 

Sensor-based methods. Whilst many methods use sensors, the simplest being temperature measurement, this terminology is often used to cover viscosity, pH, oxygen and humidity determination, etc. These are true in-line techniques and offer rapid, inexpensive real-time analysis. Humidity determination in drying ovens is a common example. 

A particularly difficult problem in microwave processing is the correct measurement of the reaction temperature during the irradiation phase. Classical temperature sensors (thermometers, thermocouples) will fail since they will couple with the electromagnetic field. Temperature measurement can be achieved either by means of an immersed temperature probe (fiber-optic or gas-balloon thermometer) or on the outer surface of the reaction vessels by means of a remote IR sensor. Due to the volumetric character of microwave heating, the surface temperature of the reaction vessel will not always reflect the actual temperature inside the vessel [7]. 

Temperature measurement is achieved by means of a fiber-optic probe immersed in a single reference vessel. An available option is an IR sensor for monitoring the outside surface temperature of each vessel, mounted in the sidewall of the cavity about 5 cm above the bottom. The reaction pressure is measured by a pneumatic sensor connected to one reference vessel. Therefore, the parallel rotors should be filled with identical reaction mixtures to ensure homogeneity. 

Temperature measurement in the rotor systems is accomplished by means of an immersed fiber-optic probe in one reference vessel or by an IR sensor on the surface of the vessels positioned at the bottom of the cavity. Pressure measurement in HP-... 

Temperature measurement is achieved by means of a remote IR sensor beneath the lower outer surface of the vessels. The operation limit of the IR sensor is 400 °C, but it is regulated by the software safety features to 280 °C as the operation limits of the materials used are around 300 °C. For additional control, temperature measurement in a reference vessel by means of an immersed gas-balloon thermometer is available. The operational limit of this temperature probe is 310 °C, making it suitable for reactions under extreme temperature and pressure conditions. 

Similar to its predecessors of the Emrys series, the operation limits for the Initiator system are 60-250 °C at a maximum pressure of 20 bar. Temperature control is achieved in the same way by means of an IR sensor perpendicular to the sample position. Thus, the temperature is measured on the outer surface of the reaction vessels, and no internal temperature measurement is available. Pressure measurement is accomplished by a non-invasive sensor integrated into the cavity lid, which measures the deformation of the Teflon seal of the vessels. Efficient cooling is accomplished by means of a pressurized air supply at a rate of approximately 60 L min-1, which enables cooling from 250 °C to 40 °C within one minute. 

Routine temperature measurement within the Discover series is achieved by means of an IR sensor positioned beneath the cavity below the vessel. This allows accurate temperature control of the reaction even when using minimal volumes of materials (0.2 mL). The platform also accepts an optional fiber-optic temperature sensor system that addresses the need for temperature measurement where IR technology is not suitable, such as with sub-zero temperature reactions or with specialized reaction vessels. Pressure regulation is achieved by means of the IntelliVent pressure management technology. If the pressure in the vial exceeds 20 bar, the... 

For accurate temperature monitoring when conducting a temperature-controlled program, a minimum filling volume of the vessels is crucial. In the case of IR temperature measurement from the bottom of a vessel, only a very small amount of reaction mixture (ca. 50 pL) is sufficient to obtain a precise temperature feedback in a monomode instrument (CEM Discover series). On the other hand, a rectangular mounted IR sensor, as used in Biotage instruments (see Section 3.5) requires a certain minimum filling volume (200 pL for the smallest reaction vials see Fig. 3.21). 

The other limit is the problem of temperature measurements. Classical temperature sensors could be avoided in relation to power level. Hence, temperature measurements will be distorted by strong electric currents induced inside the metallic wires insuring connection of temperature sensor. The technological solution is the optical fiber thermometers [35-39]. However, measurements are limited below 250 °C. For higher values, surface temperature can be estimated by infrared camera or pyrometer [38, 40], However, due to volumic character of microwave heating, surface temperatures are often inferior to core temperatures. 

In clinical settings core temperature measurements, including pulmonary artery and esophagus measurements, are often required. In 1959 Benzinger [1] first proposed the human tympanic membrane as the ideal site for core temperature measurements. The tympanic membrane is ideal, because it is located near the carotid artery and shares its blood supply with the hypothalamus, which controls body temperature. First temperature measurements in the ear were performed with thermistor sensors in direct contact with the tympanic membrane. The invasiveness of this method limited its use mainly to anaesthetized patients. 

The first clinical IRET used thermopile sensors to achieve non-contact temperature measurement in the ear. In 1991 a tympanic thermometer for home use was first introduced to the consumer market (Thermoscan HM 1). It utilized a pyroelectric sensor which requires the use of a suitable mechanical shutter or chopper mechanism, since it is only sensitive to temperature changes [3]. The main advantage of the pyroelectric sensor unit was its lower cost. However, prices for thermo-... 

A thermopile sensor generates an output voltage that depends on the temperature difference between its hot and cold contacts. For infrared temperature measurement, the hot contacts are normally thermally insulated and placed on a thin membrane, whereas the cold contacts are thermally connected to the metal housing. Infrared radiation, which is absorbed by the hot contacts of the thermopile, causes a temperature difference between hot and cold contacts. The resulting output voltage is a measure for the temperature difference between radiation source and cold contacts of the thermopile sensor. It is therefore necessary to measure also the temperature of the cold contacts by an additional ambient temperature sensor in order to determine the temperature of the radiation source. 

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