Thermocouple gauges

Figure 2. Schematic of coal liquefaction apparatus. AC2 is equipped with an internal heater and AC3 is equipped with an internal cooling coil. All autoclaves and the heated fitter are equipped with pressure gauges, thermocouples, and temperature controllers.

Freeze-dryer controls have experienced the most dramatic developments in recent years. The original mercury gauge and thermostatically controlled heaters were initially replaced with analogue vacuum gauges, thermocouples and controls. Eventually, the latter two were superseded by digital devices. 

Level gauge Thermocouple Flowmeter Pressure gaugt... 

The easiest method to measure the temperature of packages, circuit cards, and heat sinks is to mount fine-gauge thermocouples on them and take... 

Thermocouple Size. Many factors can confound the solder-joint temperature measurement process, regardless of whether the thermocouple bead is properly deployed between lead and pad. Among these are the size of the bead and the thermal mass of the thermocouple assembly. In general, the use of finer-gauge thermocouples such as 30 to 36 American Wire Gauge (AWG) (see Table 47.1) is recommended. This will permit insertion between lead and pad even at very fine lead and pad pitches. Ideally the thermocouple bead will be completely within the solder joint to be measured. 

Vacuum gauge, thermocouple gauge A vacuum gauge that uses the cooling of a heated thermocouple junction as an indicator of the gas pressme (density). 

Type J thermocouples (Table 11.58) are one of the most common types of industrial thermocouples because of the relatively high Seebeck coefficient and low cost. They are recommended for use in the temperature range from 0 to 760°C (but never above 760°C due to an abrupt magnetic transformation that can cause decalibration even when returned to lower temperatures). Use is permitted in vacuum and in oxidizing, reducing, or inert atmospheres, with the exception of sulfurous atmospheres above 500°C. For extended use above 500°C, heavy-gauge wires are recommended. They are not recommended for subzero temperatures. These thermocouples are subject to poor conformance characteristics because of impurities in the iron. 

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. 

Gauges. Because there is no way to measure and/or distinguish molecular vacuum environment except in terms of its use, readings related to gas-phase concentration ate provided by diaphragm, McCleod, thermocouple, Pitani gauges, and hot and cold cathode ionization gauges (manometers). 

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. 

Thrner gauges may be used to determine scale thickness in situ. These are Wheatstone bridge circuit devices that have proved very useful for 40 years or so. As with chloral thermocouples, calibration may be difficult, and the level of magnetic iron content (magnetite) in the deposit may affect the readings. More modem electronic versions, similar to paint thickness testers, are now available. 

A. 3-Methylenecycldbutane-l,2-dicarboxylic anhydride. A 2-1. stainless steel autoclave equipped with stirrer, pressure gauge, and thermocouple is charged with 500 g. (5.1 moles) of maleic anhydride, 645 ml. of benzene, and 0.25 g. of hydroquinone. The autoclave is closed, cooled to — 70° with stirring, and evacuated to a pressure of about 20 mm. Allene (100 g., 2.5 moles) (Note 1)... 

In Phase II (see Figure 3) we used a 2900-cc pressure vessel, with a 2000-cc glass liner in which 1000 cc of solution could be polymerized. This was a 10-fold Increase over Phase I. We used a pressure gauge similar to Phase I. There were 5 type J thermocouples. Of these, there were k thermocouples within the reactor as compared to only 1 In Phase I. Two were In the solution within the glass liner, one was between the glass liner and reactor wall, and the... 

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. 

Figure 2 Schematic diagram of a 100-mL UV-autoclave. a = gas and sampling valve, b = thermocouple, c = quartz window, d = Teflon O-rings, e = autoclave lid, f = rupture disc, g = valve and pressure gauge, h gaskets, i = autoclave body, k = glass insert, 1 = temperature control, m stirring bar. (Pmax 300 bar, Tmax = 150 °C) (Reproduced with permission from Ref. 7. Copyright 1983 Elsevier Sequoia.)...

A precision aneroid manometer is used for measurements in the 760— 1 torr range. Thermocouple gauges are used in the 1 — 1 x 10 3 range. A cold cathode ionization gauge is used in the high vacuum range down to 10-6 torr. 

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