Thermocouple control

The Ferranti-Shidey viscometer was the first commercial general-purpose cone—plate viscometer many of the instmments stiU remain in use in the 1990s. Viscosities of 20 to 3 x 10 mPa-s can be measured over a shear rate range of 1.8-18, 000 and at up to 200°C with special ceramic cones. Its features include accurate temperature measurement and good temperature control (thermocouples are embedded in the water-jacketed plate), electrical sensing of cone—plate contact, and a means of adjusting and locking the position of the cone and the plate in such a way that these two just touch. Many of the instmments have been interfaced with computers or microprocessors. 

Temperature (R) Legislation and controls Thermocouple Thermometer Resistance thermometers ASTM methods... 

The first thing to note is that the furnace surrounds the sample-holder containing the differential thermocouples. A separate control thermocouple controls the furnace temperature and should be placed as close as possible to the position of the sample holder. Some commercial manufacturers use the Reference leg of the differential thermocouple to control the temperature. However, if you were to build a DTA using the components as shown in 7.1.14,... 

The Fig. 13 g shows the sample holder with the two hot junctions of the DTA- and temperature control thermocouple. The two crucibles (sample and reference) must be placed in position so as to ensure satisfactory contact between hot junction and base of the crucible. After the experiment, any adhering cmcible should be loosened carefully by heating, and the holder freed of impurities by annealing at approx. 

A number of issues relative to the prediction of solids conveying in smooth bore single-screw extruders are exposed from the theoretical fits to the data in Fig. 5.32. First, the data needed to carry out an effective simulation is difficult to take and is very time consuming, and only a few labs have the proper equipment that is, bulk density measurement, dynamic friction data, lateral stress, and solids conveying data. Moreover, care must be taken to develop an accurate representation of the surface temperature for the barrel and screw as a function of the axial position. This would be quite difficult in a traditional extruder with only a control thermocouple to measure the temperature at the midpoint of the barrel thickness. Second... 

Thermocouples and wire leads require constant maintenance due to wire breaks and malfunctioning thermocouples. In most cases, the root cause of the problem is easy to determine. When a thermocouple loses continuity the instrument panel typically reports either an open circuit or a very negative temperature. A more difficult but also common problem occurs when the control thermocouple is not located close to the heating element on the control system. In this case, it is possible for the thermocouple to be influenced by another heated control zone while allowing its control zone to operate at temperatures that can be either very hot or very cold. Such cold conditions can cause the polymer to solidify in the transfer line while a hot condition can cause the resin to degrade. During the installation and startup of new equipment, it is important that the thermocouples are matched with the proper controller and control zone. 

An extrusion trial was performed at the processor s plant using a 38.1 mm diameter production extruder, a proprietary screw design, and resin that had previously exhibited flow surging and reduced rate. The extruder was equipped with three barrel zone heaters with control thermocouples (labeled Tl, T2, and T3) and two pressure sensors. One pressure sensor was located in the midsection (zone 2) of the barrel (P2) and the other at the end of the barrel near the tip of the screw (P3). Both transducers were positioned over the top of the screw such that a pressure variation due to screw rotation would be observed. 

Ti, or PEEK (polyether ether ketone) to allow measurements under very corrosive conditions. The separated phases pass AMX gadgets for on-line detection (radiometric, spectrophotometric, etc.) or phase sampling for external measurements (atomic absorption, spectrometric, etc.), depending on the system studied. The aqueous phase is also provided with cells for pH measurement, redox control (e.g., by reduction cells using platinum black and hydrogen, metal ion determination, etc.) and temperature control (thermocouples). 

Electrolytic Procedure. The cell is placed inside a vertical-column, Hevi-Duty, multiple furnace and is surrounded by an Inconel heat shield (Fig. 13). The temperature-control thermocouple (Pt vs. 90% Pt — 10% Rh) is located between the crucible and the heat shield and is protected by an outer ceramic tube. A calibration run is initially made without a charge in the crucible. A second thermocouple is inserted through the heat shield and centered on the cover of the electrolytic cell. This thermocouple is read directly by means of a potentiometer the temperature of this thermocouple corresponds closely to that of the melt. The temperature controller is adjusted until the second thermocouple indicates the desired temperature for the electrolysis. ... 

Type MK-2012, Fisher Scientific Co., 711 Forbes Ave., Pittsburgh, Pa. 15219. t This calibration must be done since a thermocouple cannot be placed directly into the melt, and the heat shield prevents the control thermocouple from giving an accurate temperature reading. 

If there is good communication between the heating elements and the sample or reference thermocouple junctions, then the control system can make its power adjustments based on one of those temperatures. If there is substantial insulation between these locations, which may be necessary for heat flow uniformity to both sample and reference or to permit the introduction of special gases, then a separate control thermocouple is used which is placed near the furnace windings. 

Under slower heating rates in heat-flux DSC, the deviation of sample temperature from the setpoint during a self-feeding reaction may be maintained adequately small so as to be neglected. If the furnace feedback control is set to act based on the temperature of the sample (that is the sample temperature thermocouple is the control thermocouple), then the control system may be able to allow the transforming sample to heat itself at a constant rate, and the heat input from the furnace will retreat as needed. 

In preparation for XRD, 0.50 g samples were placed in platinum pans and heated at 10°C/min in a furnace where the control thermocouple was in contact with the specimen container. Specimens were quenched by immediate exposure to room temperature then ground with a mortar and pestle to pass through a 325 mesh screen. X-ray diffraction was performed using a Philips9 x-ray diffractometer. Diffraction patterns were obtained with 29 values ranging from 20° to 60° 29. The diffracted x-rays were counted over 0.02° intervals for 2... 

A tube furnace drawn over the mullite outer casing is used to heat the contents to a specified temperature, based on a furnace control thermocouple. At the same time, a constant ac voltage2 is applied across the central heater. The microprocessor waits until temperature fluctuations (within 0.1°C, over one minute) at any of the inside or outside thermocouples are eliminated.3 At that point, steady state conditions are assumed to exist. 

Abbe refractometers with temperature controllers Thermocouple... 

CO temperature in cleaning vessel was not consistent and was hotter at the top than at the bottom Insufficient heating of CO entering vessel. Poor positioning of extractor control thermocouple Designed, fabricated and installed temperature controlled water bath with heat exchanger and repositioned thermocouples... 

Fig. 25. Chromatographic apparatus at low temperatures. T, to the liquid thermostat Ni, nitrogen under controlled pressure PP, peristaltic pump GF, gradient flasks Th, temperature controller (thermocouple) CC, collector control S, security C, cold chamber dd, drop detector FC, fraction collector. Adapted from Balny et al. (1975). Reprinted with permission of Analytical Biochemistry. Copyright by Academic Press.

A suitable temperature controller adjusted the operational constants needed for the temperature control of the furnace using an additional Pt-PtRhlO control thermocouple placed between the working and heating shafts of the furnace. 

The temperature was measured and controlled by two Pt30Rh-Pt6Rh thermocouples. The control thermocouple is placed at the outer side of the heating body and passes through the rim of the upper plate of the furnace. The measuring thermocouple passes through the lid of the furnace down to the surface of the melt. Both the thermocouples are protected by corundum capillary. Both the crucible and the inner hollow cylinder are made of Pt30Ir alloy. 

FIG. I—Cross view of the reactor and water pressure reserve. B exhaust vah-e, S specimen, U umbrella D,. D, stainless steel disks P pipe sustaining the sample holder, it is a pipe that contains the temperature measurement thermocouple T cylinder containing a specimen F isolated heating resistor and R furnace control thermocouple. 

The thermocouple built into the Harrick Model HVC-DRP cell is attached to the outside surface of the sample post at a point below the sample cup (as shown in Figure 1). In order to get a more accurate reading of the actual sample temperature, an auxiliary thermocouple (not shown in Figure 1) was epoxied into a fitting that attached to a third port in the base of the cell. The section of this auxiliary (iron/constantan) thermocouple inside the cell was strapped to the gas exit tube that runs from the upper portion of the sample post to the gas exit port, after which the tip end was bent into a small semicircle so that the tip of the thermocouple could be positioned at the surface of the powdered specimen in the sample cup. The built-in thermocouple was used as the control thermocouple, but its temperature setting was adjusted to give the desired temperature at the sample surface as measured by the auxiliary thermocouple. All temperatures reported in this paper were those measured by the auxiliary thermocouple. 

The CSTR has 1000 c.c. of capacity and it is provided with a static basket and a kinetic basket for 185 c.c. of catalyst. The reactor is equipped with three furnace control thermocouples. The inside temperature is measured by two thermocouples one at the bottom of the reactor and other in the head. 

Attaching the controller thermocouple to the bottom of the 0.125-in. aluminum platen by laminating. This was done, and the improved thermal coupling enhanced the performance of the laminator. 

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