Dual sensor temperature control

A few commercial temperature control systems are based on dual input from two temperature sensors. One temperature sensor is located in a deep well and measures temperature close to the polymer. The other temperature sensor is located in a shallow well and measures temperature close to the heater/cooler. The dual sensor temperature control can combine the advantages of deep-well-only control and shallow-well-only control, but can largely eliminate the drawbacks of these types of control. 

One dual sensor control system uses a weighted average of the signals from the two sensors. By doing this, the advantages of both deep-well and shallow-well can be enjoyed to some extent however, the same is true about the disadvantages. Another system uses two different temperature control loops. The first one uses only the deep-well sensor and controls the power to the heater. The second loop uses only the shallow-well sensor. This is a cascade loop. It does not control the heaters directly, but acts on the first loop in such a manner as to keep the temperature at the deep 

Microprocessor-based controllers offer great flexibility in that controller function can be changed readily by simply changing a few steps in the program. Thus, the controller function can be modified by changing the software without having to make any modifications to the hardware. 

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Recommendation 5. Use dual-temperature control sensors, located as near the loads as possible and tied together by a low-select system, can help productivity. One sensor about 10% into the zone should control piece temperature, and a second sensor about 15% from the zone discharge should prevent overheating. Benefits will be greater if the loads are positioned to the side of the furnace where the sensors are located. 

Progress in the development of SAW vapor sensor devices will proceed in several directions. Attempts to reduce SAW sensor noise will increase the emphasis on the use of SAW resonators and more sophisticated RF amplifier designs. Improved pac)caging schemes will be explored to reduce SAW temperature drift. Much of the temperature drift exhibited by dual SAW sensors is caused by unsymmetrical stresses imposed on the SAW devices as a result of thermal expansion of the pac)cage. Miniature temperature controllers for the SAW device may offer a brute-force fix for this problem. 

The deflection is measured by four laser triangulation sensors one is placed between the dual tyres and the other three are placed in front of the back axle. The laser between the dual tyres measures the pavement profile (maximum deflection) under axle load and the other three, spaced every 2.44 mm (8 ft), measure the unloaded pavement profile. The three lasers are mounted at approximately 1.1 m (3.6 ft) above the pavement surface into the truck body in a temperature-controlled enclosure (see Figure 16.53a). Two additional sensors are placed in front of the wheels to measure a secondary pavement deflection (Elseifi et al. 2012). 

Dual-sensor control n. An improved system for controlhng cylinder and plastic temperatures in extruders. For each heating zone, there are two temperature sensors, one in a shallow well slightly beneath the heater, the other deep, just outside the lining layer and near the plastic. An average of the two signals is used to control the electrical heat input (Eurotherm/Welex). 

FIGURE 5.30 Diagram of autonomous microfabricated GC for air monitoring. Vacuum outlet GC with ambient air as carrier gas is used to eliminate the need for compressed gases. A dual-column ensemble consisting of two 3.0-m-long colnmns with independent temperature control and stop-flow operation is used for selectivity enhancement, and a chemiresistor sensor anay is used for vapor identification. 

All tests were remotely controlled from a control room located approximately 800 m away from the test cell. All pressure, temperature, and flow data was recorded using a computer DAQ. A picture of the screen used to determine the LL in the tank is shown in Figure 9.7. Diodes were used in dual sense mode as temperature or liquid level sensors, as controlled on the right hand side of Figure 9.7. All data was scanned and recorded at 2 Hz. A camera was used to detect LAD breakdown, and the video feed was sent to the control room monitor to view the LAD output in real time. 

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. 

Because of this type of behavior, a sharp transition at stoichiometry but low sensitivity and temperature effects either rich or lean of this point, the oxygen sensor is most useful in controlling at the stoichiometric point. It is of limited usefulness at other exhaust compositions. However, as shown in Figure 5, this is exactly the point at which a three-way or dual bed catalytic converter is most efficient. Only when the exhaust composition is near the stoichiometric point will both the oxidation of the HC and CO and the reduction of the NO occur satisfactorily. 

Perry and Lee [28,29] offer an enhancement of QPA, based upon use of dual heat flux sensors and additional thermocouples in autoclave curing. This enhancement entails determining heat transfer properties during the cure, then using these properties in conjunction with PID regulatory control of autoclave temperature. Using the additional sensors, Perry and Lee employ an on-line Damkohler number in lieu of the second time-derivative of temperature to avoid exothermic thermal runaway within the prepreg stack thermoset resin. The Damkohler number is defined as ... 

In this paper we describe the application of an adaptive network based fuzzy inference system (ANFIS) predictor to the estimation of the product compositions in a binary methanol-water continuous distillation column from available on-line temperature measurements. This soft sensor is then applied to train an ANFIS model so that a GA performs the searching for the optimal dual control law applied to the distillation column. The performance of the developed ANFIS estimator is further tested by observing the performance of the ANFIS based control system for both set point tracking and disturbance rejection cases. 

Parameters that adversely affect the performance of a piezoelectric sensor include the mass of the chemical layer, built-in stress produced by the chemical layer, stress from the electrodes (clamping), and changes in temperature. A more sophisticated device such as a microprocessor-controlled dual-crystal instrument would be required to eliminate these undesirable effects [292]. 

Nanogels with pH and temperature dual stimuli-responsive properties characterized by interpenetrating polymer network (IPN) structure, based on PNIPAAm and PAAc, were also synthesized by in situ polymerization of acrylic acid and N,N-methylenebisacrylamide (Fig. 12.10). These IPN nanogels have the advantage of less mutual interference between the temperature-responsive and pH-responsive components, which is beneficial for their applications in controlled drug release and sensors [176]. 

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