Flow transducers

In the secondary loop, the flow controller compares the desired fuel gas flow rate with the measured flow rate from the flow transducer (FT), and adjusts the regulating valve accordingly. 

Of the other two load variables, we choose the process stream flow rate as the major disturbance. The flow transducer sends the signal to the feedforward controller (FFC, transfer function GFF). A summer (X) combines the signals from both the feedforward and the feedback... 

Rn-222 is produced from a dry Ra-226 source with an activity of about 2 mCi housed in a lead shield. Radon is carried from the source by means of compressed air with a regulated flow rate of 200 cnr/min. The test chamber is operated with a 75 1/min air pump located downstream (Figure 1XDroullard, et al., 1984) that exhausts to the outside of the building. The flow rate of this air pump is monitored by a mass flow transducer whose signals are converted to volumetric flow rates. 

Another source of problems are the thermal losses induced by instrumenting a typical high-temperature system. Thermocouple wiring and metallic capillary tubing to pressure and flow transducers can easily double the thermal losses of the system. Therefore, nonmetallic and thermally insulating sensor leads are required at reasonable costs for reliable operation at 1200°C. 

Such devices can be implemented within an analytical-scale SFE to control either pressure (need a pressure transducer) or flow rate (need a flow transducer) the fluid pump control system would be used to control the complementary parameter. The two control systems allow the decoupling of flow rate and pressure. The Hewlett-Packard model 7680 T contains just such a device, and similar devices are becoming available through other commercial sources. With properly implemented devices, the restrictor can become transparent to the user - providing settable control of parameters and operation that is highly reproducible and more robust to wider ranges of extractable components. 

The Aerotrak has an inherent capability to calibrate a variety of flow transducers, such as turbine, variable area, nozzles, vortex shedders, orifice plates, laminar, thermal mass flow controllers. 

The output control on the closed-loop machine operates continuously, comparing the set output value of the inverters with the real output as measured by the volumetric flow transducers. The system enables pouring only when the parameter is within the limits set by the operator via the keyboard and when it is possible to change the pump speed in less than half a second. 

In the heat flow meter technique, the sample is placed between two plates controlled at different temperatures. Thermocouples placed just below the plate surfaces measure the temperature drop across the sample. One (or more) heat flow transducers mounted on the plate measures the voltage which is proportional to the heat flow through the sample. Knowing the relationship between the voltage signal of the transducer and the heat flow through it, which can be obtained by calibrating the transducer to a known thermal conductivity standard, the thermal conductivity for the specimen can be obtained. 

This latter requirement is becoming more and more important as VIP technology moves closer to the market. Recent improvements have been based on the use of a novel dual heat flow transducer design and a tight control of plate temperatures [48]. 

Collins J, Lee AP (2004) Microfluidic flow transducer based on the measurement of electrical admittance. Lab Chip 4(1) 7-10... 

In our opinion, an experimental method, which allows use of methods with volatile modifiers is very important [76]. A mass-spectrometric (MS) detector can be tuned to measure retention time of a particular solute or group of solutes while ignoring other components including volatile modifiers [122]. The GS-MS method for adsorbable carrier gas is discussed in more detail by Parcher et al. [51]. The instrumentation is shown in Fig. 5-33 [122] Si and S2 are flow transducers, S3 and S4 are pressure transducers, and R2 are flow control valves and GSV represents a gas sampling valve used for injection of gaseous solutes. The benzene... 

Components incorporated in chemical analysis systems are rapidly being developed in micro scale. Today microstructured pumps, valves and flow channels are already available, [1]. Micro scaled flow transducers and temperature sensors as well as chemical sensors i.e. PO2, PCO2, pH, [2], have also been developed. Flow injection analysis systems commonly use enzyme reactors for the analysis of more complex components, and until recently little work has been done on the wafer integration of enzyme reactors [3,4]. 

By analogy with the control loop hierarchy, one can split the control chain into the process to be controlled and the control system, as shown (for example) in Figure 12.18. In the given example, the process consists of the tank, which can be filled, the control valve with the appropriate piping, the restrictor, the level and flow transducers and perhaps a recorder the control system covers the programmable controller, the signal transmission, and the I/P converter. 

Gas flow rates were monitored by Matheson mass flow transducers and pressures were controlled by pressure regulators. Flow rates, temperatures and reactor pressure were recorded at 10 s intervals by a data acquisition system interfaced with a Hewlett Packard 1000 mini-computer. Details regarding the reactor system will be presented elsewhere. ... 

Thomas, R. A. Flow transducers and flow cytometers for making simultaneous electronic and optical measurements on particles for identifying viable cells and budding yeast. PCX hit. Appl. WO 2007044617, 2007 Chem. Abstr. 2007, 146, 397768. 

Linearizing the output of the transmitter if necessary (e.g., square root extraction of the differential pressure for a head-type flow transducer) can be done within the instrument instead of within the control system. 

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