Pressure transducers temperature effect

The technique of gas adsorption manometry is now probably the most widely used it is simple and effective since the pressure transducer provides all the information required to determine the adsorption isotherm. Thus, the pressure and temperature of each dose of gas are measured and the gas is allowed to enter the adsorption bulb. After adsorption equilibrium has been established, the amount adsorbed is calculated from the change in pressure. The most critical features of adsorption manometry are summarized in the following checklist, with more detailed comments given in Section 3.4. 

The pressure and temperature in the reactor were measured by a K-type thermocouple inserted into the reactor and pressure transducer, respectively. The molten salt bath was bubbled with air so to obtain a homogenous temperature inside the bath and effective heat transfer. The temperature in the reactor rose quickly, exceeding 390 C in 40 s. The pressure continued to slowly increase after the temperature reached 400 C, probably due to the gas formation. 

The most straightforward method for vapor-pressure measurement is the static method, in which the pressure of the vapor above a pure liquid is measured directly with a manometer, pressure gauge, or pressure transducer. All parts of the apparatus must be maintained at a temperature at least as high as that of the sample in order to avoid condensation. Static techniques may be used at high temperatures and pressures with appropriate apparatus construction, but they become difficult at low vapor pressures due to the difficulty of pressure measurement and the effects of impurities. With good equipment and procedures, the accuracy of static vapor pressure measurements can be on the order of 0.1%. 

Some years ago D. Stuerga designed a microwave reactor, called the RAMO (reac-teur autoclave microonde), which is not a commercial device. The microwave applicator and the reactor are original. The resonant frequency of the cavity can be controlled by varying the position of a plunger. The effective cavity power can be increased by three orders of magnitude. The autoclave is made of polymeric materials, which are microwave transparent, chemically inert, and sufficiently strong to accommodate the pressures induced. The reactants are placed in a Teflon flask inserted within a polyetherimide flask. A fiber-optic thermometry system, a pressure transducer, and a manometer enable simultaneous measurement of temperature and pressure within the reactor. The system is controlled by pressure. The reactor is shown in Fig. 2.32. 

The main purpose of a capillary rheometer is to generate a viscosity-shear rate curve over as wide a range of shear rates as possible. The effect of temperature on the viscosity can also be determined by running curves across a range of temperatures. The selection of specific dies and pressure transducers tailor the shear rate range to match a desired process window. This information can be used in many ways. 

The rheometer is set up at the desired temperature and a single (or usually not more than two) shear rate at which to perform the test is chosen. Usually a low shear rate is chosen for two reasons low shear viscosity is more sensitive to the effects of degradation (the main effect is usually a reduction in the average molecular weight) and the piston speed should be low enough to allow for many tests on the same barrel of material. Make sure a proper pressure transducer is selected, one that is sensitive enough to track the low-shear measurements accurately. Perform the viscosity measurement at specified intervals until the barrel is empty or a sufficient time period is covered. 

In (10) and (25)-(34) cam-follower experiments are described. In all test rigs the cam radius was of the order of 50 mm, while the cam width was of the order of 10 to 20 mm. Film thickness is estimated from global capacitance in (10), (25), (30) and (31), and from overall contact resistance in (26). Local film thickness measurements, employing the 0.25 mm dia. gauge described in (18), are reported in (29). The loads are rather low. This paper also shows pressure measurements obtained with a 0.25 mm effective dia. piezoelectric transducer. Local pressures and temperatures can also be obtained using miniature thin film transducers, see (27), (28), (32) and (33). These transducers have a minimum width of 10 pm. To find local cam surface temperatures, an infrared scanning system was employed in (34), with a spot size of 0.45 mm. 

Melt temperature and fill rates have been demonstrated to be very important process variables for microcellular injection molding. Recent work has studied the use of fast response thermocouples along with traditional pressure transducers to determine their effectiveness in providing practical process monitoring tools for the microcellular molding process [7]. Behind the ejector pin, pressure transducers and fast... 

Steady-State Temperature Effects on Pressure Transducers... 

Like strain gauges and displacement devices, the output of a pressure transducer depends not only on the primary input, in this case pressure, but also upon extraneous effects, such as the effect of temperature on its various components. We shall examine these latter effects in the following paragraphs. 

Figure 8.5 shows the steady-state temperature effects on two common cryogenic pressure transducers. These data were obtained by simply calibrating the pressure transducer at three different fixed temperatures, after a sufficient amount of time had elapsed to ensure constant temperature for every component of the transducer. Note both changes in sensitivity and zero shifts. 

Fig. 8.5. Representative steady-state temperature effects on pressure transducers. ...

As mentioned, Fig. 8.5 shows temperature effects at steady state after all members of the pressure transducer have come to thermal equilibrium with one another. Tests show that several minutes may be required for thermal equilibrium to be established. During this period of thermal shock, temperature effects are a combination of the two steady-state effects shown namely zero shift and sensitivity shift. It is not unusual for a pressure transducer to show a false output of 85% of full scale during this transition period. Accordingly, avoiding thermal shock effects is most important for making a valid measurement. 

The most common solution to temperature effects is to avoid extreme-temperature environments. When the pressure instrumentation point is subjected to such temperatures, the standard procedure is to run tubing from the pressure source to a remote, stable temperature location. This is a good procedure if a frequency response of the order of 10 Hz is desired. The tubing with attached transducer acts approximately like an organ pipe or a... 

In the study of atmospheric temperatures and composition one is often interested in the emission from a particular atmospheric constituent. For the analysis of the vertical temperature profile on Earth, Venus, and Mars, thermal emission from the CO2 molecule can be used. If the same gas is contained in the absorption cell, the radiation of interest is being filtered out. How does one measure the radiation that has just been removed from the beam This can be accomplished in several ways. For example, consider an absorption cell with two windows on opposing ends exposed to a beam of radiation. Wavenumbers outside the gas absorption band and in the transparent gaps between lines will penetrate the cell without a noticeable effect. Radiation within the width of strong lines will be absorbed and will cause a temperature rise in the gas. The corresponding pressure increase may be registered by a sensitive pressure transducer. The resulting infrared detector is sensitive only to radiation specifically tuned to the gas in the cell. Such detectors have been produced (the Patterson-Moos cell), but have, as far as we know, never been applied to planetary work. 

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