Analogue input/output

Content of user displays Levels of user access for different user groups Digital/analogue inputs/outputs to external equipment Serial inputs/outputs to external equipment Parallel communications to external equipment Network communications to external equipment... 

Four serial (RS232) ports are provided for flexible communications to other instruments, i.e. autosamplers. In addition, five analogue inputs, tvsro analogue outputs and 3 TTL input/outputs are provided to ensure complete flexibility. These allow auxihary instruments under direct control and the abihty to process data generated by these in real time. These features extend the range of facihties on these expensive but worthwhile analytical techniques. There is no doubt that future developments in computing will continue to have a radical impact on these instrumental systems. 

The type of the input/output files is the ordinary MS DOS or Windows text filetype, corresponding to the. txt extension. This enables one to edit the files using familiar editors. Also, this feature makes it easy to produce initial files of experimental data automatically, via any suitable analogue-to-digital data converter. 

Consider the simple linear electrical network depicted in Fig. 4.19. It can be viewed as an electrical analogue of the coupled hydraulic tank system considered in Section 4.4.1. A bond graph of the direct model with the two inputs I(t) and E(t) and the two outputs e and /2 appears in Fig. 4.20. There is one set of two disjoint input-output causal paths... 

The AD-interface connecting the analyser and the data unit is an 8-channel serial AD-interface with 12-bit resolution. The ADC is based on a Linear Technology chip (LTC1290) and requires only a few additional components (a print board, complete with all components can be purchased for about 50 US from Conrad Electronic, D-92240 Hirschau). This interface is connected to a maximum of 8 spectrophotometer analogue outputs (or other instruments, e.g., an attached conductivity sensor) and to a serial port of the PC. One of the analogue inputs reads the sampler status. A serial ADC allows longer distance between wet analysis and dry data treatment (about 15 m). If parallel ADC interface cards mounted in the computer are used, the wet-analyser and computer have to be close together (less than 5 m). No additional hardware is required. 

Figure 2. Schematic representation of the reactor system computer-controlled pumps (PI, P2) pump controllers (fc) reactor (CSTR) reception vessel valves (S1-S4) monomer and initiator storage vessels (Tl, T2). (a) Digital input from GPC injection valve (b) analogue output from GPC (c, d) digital outputs to recorder chart drive and event marker (e, f) analogue outputs for pump set-point adjustment (g,h) reactor feeds (i) reactor output (j-m) digital outputs to reception system valves (n) manual sampling of products by GPC,...

A multichannel analyzer (MCA) with a minimum of 4096 channels should be connected to a keyboard and display screen for input and output of data and interaction with a computer. Several kits are available for the conversion of personal computers (PCs) into MCAs. Basically there are three types of conversion kits. One makes use of board with an analogue-to-digital converter (ADC) that simply clips into the PC a second type uses a clip-in board with an external ADC and the third type uses a multichannel buffer (MCB) connected to the PC. All of these PC-based MCA systems are relatively inexpensive and are very suitable for use in germanium and sodium iodide y-ray spectrometry. 

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