Sensors temperature

Two common type of sensors are used for temperatures in the ranges experienced in plastic processing equipment the thermocouple (TC) and the 

The RTD sensor is based on the fact that the resistance of some metals changes markedly with temperature, whereas the resistance of platinum, the metal most commonly used in RTDs, is extremely stable. Its variation in temperature is both repeatable and predictable to a high degree of accuracy. In the past, TCs offered major cost advantages but with the advent of low-cost solid state dc amplifiers, the use of RTDs has become more realistic. 

In power compensated DSC the small size of the individual sample and reference holders makes for rapid response. The temperature sensors are platinum (Pt) resistive elements. The individual furnaces are made of Pt/Rh alloy. It is important that the thermal characteristics of the sample and reference assemblies be matched precisely. The maximum operating temperature is limited to about 750 °C. High temperature DSC measurements (750-1600°C) are made by heat flux instruments using thermocouples of Pt and Pt/Rh alloys. The thermocouples often incorporate a plate to support the crucible. The use of precious metal thermocouples is at the expense of a small signal strength. Both chromel/alumel and chromel/constantan are used in heat flux DSC equipment for measurements at temperatures to about 750 °C. Multiple thermocouple assemblies offer the possibility of an increased sensitivity - recently a 20-junction Au/Au-Pd thermocouple assembly has been developed. Thermocouples of W and W/Re are used in DTA equipment for measurements above 1600°C. The operating temperature is the predominant feature which determines the design and the materials used in the con- 

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Modern subsea trees, manifolds, (EH), etc., are commonly controlled via a complex Electro-Hydraulic System. Electricity is used to power the control system and to allow for communication or command signalling between surface and subsea. Signals sent back to surface will include, for example, subsea valve status and pressure/ temperature sensor outputs. Hydraulics are used to operate valves on the subsea facilities (e.g. subsea tree and manifold valves). The majority of the subsea valves are operated by hydraulically powered actuator units mounted on the valve bodies. 

Figure Bl.27.4. Rotating bomb isoperibole calorimeter. A, stainless steel bomb, platinum lined B, heater C, thermostat can D, thennostat iimer wall E, themiostat water G, sleeve for temperature sensor H, motor for bomb rotation J, motor for calorimeter stirrer K, coimection to cooling or heating unit for thennostat L, circulation pump.

Exhaust gas temperature sensor Catalytic substrate Heat insulator... 

Temperature. Temperature sensor selection and installation should be based on the process-related requirements of a particular situation, ie, temperature level and range, process environment, accuracy, and repeatabiHty. Accuracy and repeatabiHty are affected by the inherent characteristics of the device and its location and installation. For example, if the average temperature of a flowing fluid is to be measured, mounting the device nearly flush with... 

H. B. Sachse, Semi-Conducting Temperature Sensors and Their yTpplications ]oEn. Wiley Sons, Inc., New York, 1975. 

One system for measuring catalyst failure is based on two oxygen sensors, one located in the normal control location, the other downstream of the catalyst (102,103). The second O2 sensor indicates relative catalyst performance by measuring the abiUty to respond to a change in air/fuel mixture. Other techniques using temperatures sensors have also been described (104—107). Whereas the dual O2 sensor method is likely to be used initially, a criticism of the two O2 sensors system has been reported (44) showing that properly functioning catalysts would be detected as a failure by the method. 

Improved sensors allow computer monitoring of the system for safety and protection of the equipment from damage. Sensors include lubrication-flow monitors and alarms, bearing-temperature sensors, belt scales, rotation sensors, and proximity sensors to detect ore level under the crusher. The latter prevent jamming of the output with too high an ore level, and protect the conveyor from impact of lumps with too low an ore level. Motion detectors assure that the conveyor is moving. Control applied to crusher systems including conveyors can facilitate use of mobile crushers in quarries and mines, since these can be controlled remotely by computer with reduced labor. 

Endurance Burn Under certain cou(itious, a successfully arrested flame may stabilize on the unprotected side of an arrester element. Should this condition not be corrected, the flame will eventually penetrate the arrester as the channels become hot. An endurance burn time can be determined by testing, which specifies that the arrester has withstood a stabilized flame without penetration for a given period. The test should address either the actual or worst-case geometry, since heat transfer to the element will depend on whether the flame stabilizes on the top, bottom, or horizontal face. In general, the endurance burn time identified by test should not be regarded as an accurate measure of the time available to take remedial action, since test conditions will not necessarily approximate the worst possible practical case. Temperature sensors may be incorporated at the arrester to indicate a stabilized flame condition and either alarm or initiate appropriate action, such as valve closure. 

Monitoring The differential pressure across the arrester element can be monitored to determine the possible need for cleaning. The pressure taps must not create a flame path around the arrester. It can be important to provide temperature sensors, such as thermocouples, at the arrester to detect flame arrival and stabilization. Since arrester function may involve damage to the arrester, the event of successful function (flame arrival) may be used to initiate inspection of the element for damage. If the piping is such that flame stabihzation on the element is a realistic concern, action must be taken immediately upon indication of such stabihzation (see also Endurance Burn ). Such action may involve valve closure to shut off gas flow. 

FIG. 29-68 Axial (thriistj oil-film hearing watL tilting pads and emhedded temperature sensors. 

Install high temperature sensors interlocked to shut down reactor... 

Install vibration or temperature sensor with alarm Install emergency relief device (ERD)... 

Heat build-up Monitor and alarm temperature due to loss of, coolant flow/temperature sensors or product cooling. temperature sensors. CCPS G-12 CCPS G-23 CCPS G-29... 

Select temperature sensors that can be used with multiple heating/cooling media over a wide temperature range without loss of performance... 

A thermistor is a thermally sensitive, semiconductor solid-state device, which can only sense and not monitor (cannot read) the temperature of a sensitive part of equipment where it is located. It can operate precisely and consistently at the preset value. The response time is low and is of the order of 5-10 seconds. Since it is only a temperature sensor, it does not indicate the temperature of the windings or where it is located but only its preset condition. 

Dommer. R. and Rotter, N W., Temperature sensors for thermal over-load protection of machines, Siemens Circuit, XVII, No. 4, October (1982). 

Afterburn Control. Afterburn is the term for carbon monoxide burning downstream of the regenerator this causes an increase in temperature upstream of the expander. Temperature sensors in the gas stream cause the brake to energize. This provides sufficient resisting torque to prevent acceleration until the afterburn is brought under control by water or steam injection. 

Turbomaehinery operating pressures, temperatures, and speeds are very important parameters. Obtaining aeeurate pressures and temperatures will depend not only on the type and quality of the transdueers seleeted, but also on their loeation in the gas path of the maehine. These faetors should be earefully evaluated. The aeeuraey of pressure and temperature measurements required will depend on the analysis and diagnosties that need to be performed. Table 19-2 presents some eriteria for seleetion of aerothermai instrumentation of pressure and temperature sensors for measurement of eompressor effieieney. Note that the pereentage aeeuraey requirements are more eritieal for temperature sensors than pressure sensors. The requirements are also dependent on the eompressor pressure ratio. 

Criteria for Selection of Pressure and Temperature Sensors for Compressor Efficiency Measurements... 

Temperature sensors, sueh as RTDs (Resistanee Temperature Deteetors), thermoeouples, and thermistors, ean be installed direetly in the thrust bearing to measure metal temperature. The installation shown in Figure 21-9 has the RTD embedded in the babbitted surfaee. It is in the most sensitive... 

A critical installation should have the metal temperature sensors in the thrust pad. Axial proximity probes may be used as a backup system. If metal temperatures are high and the rate of change of those temperatures begins to alter rapidly, thrust-bearing failure should be anticipated. 

Figure 8-27. Typical radial bearing temperature sensor installation.

Figure B-29. Radial bearing with a temperature sensor installed. Courtesy of A-C Compressor Corporation)...

Figure Thrust bearing pad with a temperature sensor installed. (Courtesy of Turbocare, A Division of Demag Delavaf Tuibomat inery Corp., Houston facing...

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