Computer data acquisition system

The electrochemical cell for the polarographic measurements had a four-electrode configuration equipped with a microsyringe, and was connected to a computer-assisted data-acquisition system [7]. On the other hand, the cyclic voltammetric measurements that are also assisted by a computer data-acquisition system were carried out using a gel electrode that contains the aqueous phase [8]. The cell structure was as follows ... 

A potentiostat is relatively expensive, especially if high power is needed. A cheaper method is to use the galvanostatic operation and to measure continuously the potential and to adapt the cell current manually (or using a computer data acquisition system) in order to adjust the... 

The available data from emulsion polymerization systems have been obtained almost exclusively through manual, off-line analysis of monomer conversion, emulsifier concentration, particle size, molecular weight, etc. For batch systems this results in a large expenditure of time in order to sample with sufficient frequency to accurately observe the system kinetics. In continuous systems a large number of samples are required to observe interesting system dynamics such as multiple steady states or limit cycles. In addition, feedback control of any process variable other than temperature or pressure is impossible without specialized on-line sensors. This note describes the initial stages of development of two such sensors, (one for the monitoring of reactor conversion and the other for the continuous measurement of surface tension), and their implementation as part of a computer data acquisition system for the emulsion polymerization of methyl methacrylate. 

A new method of surface tension determination has been developed which is continuous, automated, compatible with computer data acquisition systems, and capable of monitoring flowing process streams. The method is a variant of the well-known maximum bubble pressure technique. To illustrate the principles, we will describe the simplest initial configuration of the instrument here. Further details and a description of a refined version of the instrument will be reported later. 

A computer data acquisition system or an X-Y recorder capable of processing a 0-10 millivolt analog signal. 

The out-of-balance signal caused by the presence of sample vapor in contact with the sensor is amplified and fed to a recorder or computer data acquisition system. For maximum sensitivity hydrogen should be used as the carrier gas, but to reduce fire hazards, helium can be used with very little compromise in sensitivity. The sensitivity of the katherometer is only about 10 g/ml (probably the least sensitive of all GC detectors) and has a linear dynamic range of about 500 (the response index being between 0.98 and 1.02). Although the least glamorous, this detector can be used in most GC analyses that utilize packed columns and where there is no limitation in sample availability. The device is simple, reliable, and rugged and, as already stated, relatively inexpensive. 

The Electrical Conductivity System consists of a frequency generator (the frequency is usually between 1,000 and 5,000 Hz) that provides an AC potential across the cell. As already discussed, an AC potential must be used to avoid electrode polarization. The sensor is usually placed in one arm of a Wheatstone bridge as shown in figure 3. The out-of-balance signal is then rectified with a precision rectifier and the DC signal either passed to nonlinear amplifier or a computer data acquisition system. The non- linear amplifier modifies the signal so that the output is linearly related to ion concentration. Alternatively, if the output from the precision rectifier is passed directly to the... 

In most computer data acquisition systems there is an iterative program that allows the user to identify the reference and sample chromatograms and the pertinent peaks for processing. The software will then carry out the necessary calculations and provide the output in the form of a printed analytical report. 

A number of sensor arrays consisting of an assortment of commercial metal oxide gas sensors have been reported [45 7], For controlled tests, the sensors are mounted in an air-tight chamber fitted with gas inlets and outlets for controlled gas flow. Each sensor s heating element is controlled externally and resistance changes of the gas sensors are monitored by a computer data acquisition system. A significant effort in this area exists at the University of Warwick, Coventry, where for many years, sensor arrays, made from discrete Sn02 sensors or miniature integrated sensors, have been studied for ultimate application to food quality and food process control [47, 48]. 

Figure 10-13. Remote computer/data acquisition system.

Low-level input sensors such as thermocouples, turbine meters, speed transmitters and a number of process analyzers complicate system selection. Signal conditioning equipment is required for low-level inputs to both the back-up system and computer data acquisition systems. If the system is to be installed as an intrinsically safe system, multiple grounding requirements conforming to intrinsic safety grounding must be referenced to the same safety ground to avoid multiple ground problems. 

Figure 3 A typical photoelectron spectroscopy system using a flood x-ray source and a hemispherical sector energy analyzer with electron preretardation. The system is shown with a computer data acquisition system.

Mapping of the brain electric activity using more densely spaced sets of electrodes has been accomplished in combination with computer data-acquisition systems. Maps of the instantaneous distribution of bioelectricity over the head are a research tool used to help study the functionality of the brain. 

Because the current is not constant during the potentiostatic operation, it has to be integrated during the experiment for calculating the charge transfer and the current efficiency. Coulometers or electronic integrators are commercially available. If a computer data acquisition system is used, the current integration is possible by software. 

All transducers were monitored using a remote computer data acquisition system. There were separate video recordings (two to five cameras) made (Nind, 1996) as well as infrared thermal image records of the fireballs formed (Hawksworth and Brearley, 1996). British Gas additionally made wide- and narrow-angle thermal radiation measurements (Gosse and Pritchard, 1996). 

It is best, therefore, to plot pressure with a chart recorder or better, to monitor the variation of pressure with a computer data acquisition system. A simple analog or digital display of pressure is much less useful. 

SO2 removal capacity of the sol-gel derived sorbents was also studied in a fixed-bed adsorber system, which includes an adsorber column packed with sorbent pellets, a feed flow control system, and a sulfur analyzer (HORIBA, PIR-2000). A computer data acquisition system was incorporated into this adsorber system in order to obtain continuous breakthrough curves of SO2. The fixed-bed was made from dense y-A Os tube of 6 mm ID and 8 mm OD. The central portion of the bed was packed with the sorbent, with both ends of the bed filled with quartz particles (0.5 mm in diameter). The feed was air containing 2000 ppm SO2, and the fixed-bed temperature was 400°C. 

At least 10 seconds before the element drop, the reactor operations staff will start the computer data acquisition system to record reactor power at 10 millisecond intervals. 

For field measurements, it is necessary to use a probe that enters the vessel with a special probe retrieving device (Fig. 5.22). Several commercially available probes (Fig. 5.23) and analyzing systems can be directly interfaced with remote computer data-acquisition systems. 

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