Pressure measurement thermocouple gauges

Figure 4.4.5. DifFerential vapor-pressure apparatus. 100 ml Pyrex flasks connected (a) to a differential pressure transducer (c) with digital readout (d) and (b) to vacuum pump (e) and absolute pressure vacuum thermocouple gauge (f). The constant temperature in the water bath is maintained by a temperature controller (g). The transducer and cormecting glassware are housed in an insulated box (i) and kept at constant temperature shghtly above the measuring temperature by controller (j). Polymer solution and pure solvent (here water) are stirred by underwater magnetic stirrers (h). [Reprinted with permission from Ref. 66, Copyright 1989, American Chemical Society].

Conventional high pressure NICI spectra were obtained using a Hewlett-Packard 5985B quadrupole GC/MS, as described previously (1). Methane was used as the Cl reagent gas and was maintained in the source at 0.2-0.4 torr as measured through the direct inlet with a thermocouple gauge. A 200 eV electron beam was used to ionize the Cl gas, and the entire source was maintained at a temperature of 200° C. Samples were introduced into the spectrometer via the gas chromatograph which was equipped with a 25 meter fused silica capillary column directly interfaced with the ion source. For all experiments, a column coated with bonded 5% methyl phenyl silicon stationary phase, (Quadrex, Inc.) was used and helium was employed as the carrier gas at a head pressure of 20 lbs. Molecular sieve/silica gel traps were used to remove water and impurities from the carrier gas. 

For our system we chose the simplest approach — a fast sample conduit with quick quench into an evacuated sample container. For temperature measurements we used a similar probe outfitted with platinum/6% rhodium-platinum/30% rhodium thermocouple. For pressure measurements the same general type probe mentioned was employed but without extracting samples. This probe had one hole opening perpendicular to the longitudinal axis of the probe such that when inserted into the reactor it could be rotated 360°. In this manner the pressures were read from a precision pressure gauge with the opening facing 0°, 90°, 180°, and 270° relative to the direction of flow in the reactor. 

The high-pressure inlet is attached to a f in. cross to provide ports for gas introduction, pressure measurement, and thermocouple placement just in front of the frit. The Bourdon gauge (0-10 bar) should be connected via a tee to a purge valve to facilitate gas changes. Before use the assembly should be tested at 10 bar for leaks. Thermal insulation such as glass wool should be wrapped around the frit assembly to keep the expansion as adiabatic as possible. 

The pressures were measured on a thermocouple gauge calibrated with a McLeod gauge, using dry air. (Pressure gauges and diffusion pumps will be discussed later in this chapter.)... 

The decomposition temperatures of hydrates were measured by means of differential thermal analysis (DTA) under the conditions of excess gas in a stainless steel flask that was developed specially for the investigation of hydrate formation with a gaseous guest at high hydrostatic pressure. The hydrate decomposition temperature was measured with a chromel-alumel thermocouple to the accuracy of 0.3 K. The thermocouple was calibrated with the use of temperature standards. Pressure was measured with a Bourdon-tube pressure gauge. The error of the pressure measurements did not exceed 0.5 %. This procedure was described in more detail previously.The gases used in the investigation... 

Let the system pump down to whatever is its natural lowest pressure. If a Pirani or thermocouple gauge is attached to the system, measure this pressure every few minutes to determine how fast a system of this size can be pumped out. When the oil temperature reaches 200 C, continue the distillation for another 30 minutes. 

Figure 5.10 I Schematic diagram of a thermocouple gauge. An electric current heats the filament, and a thermocouple monitors the filament s temperature. Gas molecules coUide with the filament and cool it. So the higher the pressure, the lower the filament temperature will be. A readout circuit usually converts the measured filament temperature into pressure units for display.

Pressure measurement for piping and vessels is achieved by the installation of dial indicators or by distributed control systems. The piping and vessels are tapped at the required location and furnished with a 3/4-in threaded or flanged conneaion and a block valve. Tbe dial indicator is screwed into the block ralve if a remote readout system is required, the valve becomes the sensing connection. Like the thermocouple, the dial can be either fixed or swivel-headed to fecilitate readout. A dual local indicator and transmitter s) em needs only one tapping point. Exhibit 14-9 depicts a typical pressure gauge and a dual-pressure system hookup. 

Thermocouple gauge (vacuum technology) A pressure gauge that measures gas density by the cooling effect on a thermocouple junction. See also Vacuum gauge. 

Standard commercial iastmmentation and control devices are used ia fluorine systems. Pressure is measured usiag Bourdon-type gauges or pressure transducers. Stainless steel or Monel constmction is recommended for parts ia contact with fluoriae. Standard thermocouples are used for all fluorine temperature-measuriag equipment, such as the stainless-steel shielded type, iaserted through a threaded compression fitting welded iato the line. For high temperature service, nickel-shielded thermocouples should be used. 

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. 

The ARC is controlled by its own hardwired control module. The temperature is monitored by a set of seven thermocouples connected in series which measure the difference between the temperature of the sample and that of its surroundings. The temperature is maintained by heaters which receive their inputs from the control module. A pressure transducer is attached to the sample container, giving both an analog readout on a pressure gauge and a digital readout on the control module panel. It should be noted that pressure is monitored but it is not part of the control loop. 

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