Analog-digital board

In the analysis section, CH4, CO and CO2 concentrations are monitored with an online NDIR multiple analyzer (Advance Optima, Uras 14). For the analysis of O2 a continuous paramagnetic analyzer (Advance Optima, Magnos 106) is employed H2 is analyzed with a thermal conductivity detector (Advance Optima, Caldos 17). An analog-digital board (National Instruments, AT-M lO 64E) allows... 

To have the PSC under real time control of the algorithm, a computer controlled measurement system must be used. The one employed by Young consisted of an S-100 based data logging system with twelve bit analog-to-digital and digital-to-analog converter boards a power... 

Analog/digital converter boards can be very useful to incorporate instruments having no communication channel but allowing data to be obtained from their recorder outputs. This facilitates the use of obsolete laboratory instruments. Their greatest weakness is that communication is one-way (from the instrument to the computer, so the former cannot be controlled by the latter). 

In the event that current integration equipment is not available, it is still possible to conduct a quality coulometry experiment by observing the decay of the electrolysis current with time as suggested by MacNevin and Baker [71]. The electrolysis current can be monitored by using a simple strip-chart recorder or a personal computer (PC) equipped with a simple analog-to-digital (A/D) conversion board. Equation 3.49 can be rewritten as... 

The A/D board can reside either in the detector, an interface box, or in the computer. If the board is in the computer, it will have analog input terminals similar to a strip chart recorder or it will be connected to an interface box that will have this type of connector. If the A/D card is in the detector, the detector will have some type of digital interface port and a cable to connect it to the computer. In the personal computer world, once the signal is digitized outside the computer, it will be sent to the computer over one of three types of communication cables parallel, serial, or GPIB. 

A test system, controlled by personal computer (PC), was developed to evaluate the performance of the sensors. A schematic of this system is shown in Figure 3. The signals from the sensors were amplified by a multi-channel electrometer and acquired by a 16 bit analog to digital data acquisition board at a resolution of 0.0145 mV/bit. The test fixture provided the electrical and fluid interface to the sensor substrate. It contained channels which directed the sample, reference and calibrator solutions over the sensors. These channels combined down stream of the sensors to form the liquid junction as shown in Figure 1. Contact probes were used to make electrical connection to the substrate. Fluids were drawn through the test fixture by a peristaltic pump driven by a stepper motor and flow of the different fluids was controlled by the pinch valves. 

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