Chapter 1: Introduction
Analog Input Multiplexer, Model AIM-16, is installed external to the computer. The AIM-16 accepts, preamplifies, and multiplexes up to 16 analog input signals before passing them to an analog-to-digital converter typically located in an I/O slot in a PC/XT/AT type host computer. This allows direct sensor interface without jeopardizing the quality of gathered data. The AIM-16 provides screw-terminal terminations and input signal conditioning for a variety of sensors including thermocouples (J,K,T,E,S,R, and B), three-wire RTDs (both for 392- and 385-alpha), and strain gages as well as DC voltage and current inputs. For strain gage applications, +10V at up to 220mA excitation voltage for the strain gages is provided by the ACCES Model AD12-8 analog-to-digital converter through the AIM-16. That excitation voltage is available at a 2-position screw-terminal block labeled REF OUT.
An input, when selected by the input multiplexer, is filtered, amplified, and, if required, level shifted. After this processing, the signal is supplied to an output channel where it is passed to the analog-to-digital converter. The A/D converter digitizes the DC signal and presents it to the computer CPU for further processing and/or display.
A major feature of this card is that it can be used with mixed-range analog inputs. The AIM-16 provides extensive programming flexibility for both hardware and software configuration. Four digital input lines are used for channel selection and three digital input lines are used for gain selection. Gains may be selected by software or manually by switch. When selected manually, the gain setting chosen applies to all input channels.
Software included with model AD12-8 analog-to-digital converter facilitates interface to the AIM-16. That software includes setup programs, drivers, and sample programs. Read sections Installation and Software for more details.
The AIM-16 card may be used as part of a large data acquisition system. A system may comprise one to eight of these cards, all interconnected on the same output bus because each card has two parallel input/output connectors. For thermocouple measurements, each card may provide it's own reference junction compensation at input IN0 by using jumpers marked "TMP" as described in Installation. Also, for thermocouple applications, a break-detect circuit is activated by installation of a pair of shorts for each thermocouple input channel.
Option P consists of a DC-DC converter which operates from the +5VDC computer power supply and provides isolated ±15VDC for use by the analog circuits on AIM-16. This option is particularly useful if the ±12VDC computer power is noisy and/or is marginally low.
Model AIM-16I has current-sensing resistors installed for use in 4-20mA applications. Further, it has also been modified so that maximum resolution is provided at the A/D converter. The modifications that are made include introduction of an offset and addition of a gain adjustment pot, so that full 12-bit resolution is provided. Model AIM-16R is specifically modified to provide the best possible accuracy for RTD inputs.
