Temperature programed heaters

Special high-temperature probes reaching up to 1000°C are also available. Modem direct probes have temperature programed heaters [27] allowing to set rates of 5-150°C min or are equipped with ion current-controlled heaters [28]. 

Other thermal zones which should be thermostated separately from the column oven include the Injector and detector ovens. These are generally insulted metal blocks heated by cartridge heaters controlled by sensors located in a feedback loop with the power supply. Detector blocks are usually maintained at a temperature selected to minimize detector contamination from condensation of column bleed or sample components and to optimize the response of the detector to the sample. The requirements for i injectors may be different depending on the injector design and may include provision for temperature program operation. 

In this method, the components of a reactive mixture are thermally conditioned and mixed at a low temperature, which retards the reaction during the preparatory stages. The working cell of a viscometer is thermally conditioned at the same temperature. When the sample is placed in the measuring device, a programmed heater controls the temperature changes. In the simplest case, the temperature changes linearly as ... 

All activity measurements were conducted in an in-situ infrared reactor cell placed in the sample compartment of a DIGILAB 15C Fourier Transform Infrared (FTIR) Spectrometer. The reactor, described in detail elsewhere [11], consisted of two aluminum flanges with CaF2 IR transparent windows, a gas inlet and outlet, and two foil fast response thermocouples which were placed in direct contat with the catalyst. The reactor temperature was maintained constant by external heaters controlled by a temperature programmed controller. A Teflon coated recycle pump permitted to maintain near isothermal conditions and improve the mixing in the reactor. The reactor and associated lines were tested for activity at the highest temperature used, and it was found to have negligible activity. 

Peripheral equipment further purifies, meters, and preheats the hydrocarbon feed, the nitrogen used for flushing, the air for catalyst regeneration, and the hydrogen for catalyst reduction. Two preheaters are used to preheat the feed to proper reaction temperature. The heaters are programed to minimize hydrocarbon decomposition before it enters the reaction zone of the reactor. An electrically heated aluminum-bronze block serves as a heat sink which provides adequate temperature control to the catalyst bed. A second flow reactor, heated by an electric furnace and located in series with the main reactor, is an isomerization reactor that produces an equilibrium mixture of n-butenes. 

Samples were heated on a Zeiss hot stage, modified by replacing the platinum sample temperature thermocouple by a more sensitive copper-constantan couple, located as close as possible beneath the sample cover slip. A second temperature program thermocouple was placed in contact with the ceramic heater frame of the hot stage. The stage was programmed at 2°C. per minute with a slope-proportional band controller. Temperature was controlled to 0.05°C. Ice reference junctions were used on both samples and program thermocouples. The output of the sample-ice junction thermocouple was recorded on the 0.5 mv. per inch z-axis of the Moseley x-y recorder. 

FIGURE 31 -11 Power-compensated DSC sample and reference holders and heaters. A temperature program is generated by the computer system. Platinum resistance thermometers, in contact with the sample and reference holders, sense any difference between the programmed temperature and the temperatures of the sample and reference, The error signal ts used to adjust the power applied to the sample and the power applied to the reference platinum resistance heaters. The DSC output signal is the difference in the power required between the sample and the reference so that bolh equal the programmed temperature. 

The desorber heater and the drift tube with the drift gas can be operated at a variety of temperatures. In general, the desorber temperature is 210°C, but some explosives will decompose at these temperatures and thus must be desorbed at lower temperatures. Programmed temperature desorption appears to be a promising approach for obtaining IMS spectra of a broad range of explosives as well as for simple and quick graduated thermal desorption to differentiate between compounds of different volatility. 

The sample is positioned in a temperature-control chamber which contains a radiant heater and a coolant distribution system. The radiant heater provides precise and accurate control of sample temperature. The coolant distribution system uses cold nitrogen gas for smooth, controlled sub-ambient operation and for quench cooling at the start or end of a run. Both the radiant heater and the coolant accessory are controlled automatically by the 983 system to ensure reproducible temperature programming. An adjustable thermocouple, mounted close to the sample, provides precise feedback information to the temperature controller, as well as a readout of sample temperature. 

Wolf, Bohmhammel, and Wolf (1998) described the constmction of a fully automated adiabatic calorimeter for the temperature range of 15-300 K with a helium refrigerator system. A computer program controls the complete measurement, calculates Cp for each heating step, and displays the respective temperatures of the sample and radiation shield as a function of time and Cp/Tas a function of temperature. The heater current is automatically adjusted to the respective heat capacity to get the proper temperature step. 

The underlying temperature of the experiment, typically linear with time or constant, is applied by temperature control of the surrounding furnace to which the calorimeter chip is connected. The heater, which is part of the chip, is used for further temperature programs such as continuous (scanning) or periodical or pulse-like heating. 

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