Model AIM-16 accepts, pre-amplifies, and multiplexes analog signals for application to an analog-to-digital converter installed in a host computer. Each AIM-16 concentrates 16 differential analog input channels into one single-ended analog output channel. Up to eight AIM-16s can be cascaded providing total capacity for 128 inputs to an “8-input A/D Converter.” There are several variants of this card. These will be identified in bold faced type in the following paragraphs.
A high grade instrumentation amplifier provides gains from 0.5 up to 1000. Gain is software programmable channel-by-channel. Alternatively, manual switches may be set to provide the same gain for all inputs. If all inputs are to be the same full-scale range, you may specify AIM-16M (“M” for manual gain setting). This is lower priced than other models. Thermocouple measurements require not only amplification but also cold junction compensation and open-thermocouple or break detection. An on-board junction-temperature sensor is normally jumpered to the first input channel and an open or break-detect signal is available by installing two jumpers for each channel where break detection is desired.
Three-wire RTD measurements are accomplished by adding two jumpers per channel. In order to provide extended range and resolution, an offset is introduced via a jumper. When this is done, all channels on the card are affected. With 5 VDC offset introduced RTD measurement range is -38° to 420°C with resolution to approximately 0.1°. With 10 VDC offset introduced measurement range is -200° to 680°C with resolution of approximately 0.2°. Without the offset, range is -200° to 680°C with resolution to about 0.4° C. If all inputs are to be from 100-ohm RTD’s then you can specify AIM-16R and you will get a card that has been modified to provide best possible accuracy for those RTD’s.
Ratiometric reading of a strain gage requires input to two channels: one measures sensor excitation and the other reads sensor output. The host computer can then compute the output as a ratio of sensor output and a gain of 1 is used for excitation. When AIM-16 is used with ACCES Model AD12-8 or Model RAG128, the buffered A/D converter reference voltage is available at screw terminals on the AIM-16. That precision voltage can provide up to 220 mA excitation current for the strain gages.
For reading current inputs, AIM-16 has provisions on the card for 16 precision resistors. It is only necessary to install a resistor of proper value and to set a gain appropriate for each current-input channel. Alternatively, if all inputs are to be from standard 4-20 mA current transmitters, the AIM-16I version of this card includes the resistors and is specially set up at the factory to give full 12-bit resolution at the A/D converter which will receive the AIM-16I output.
For voltage inputs, voltages should be within the range of ±10 VDC and gains selected which are compatible with the full-scale rating of the host A/D converter. AIM-16 uses ±12 VDC computer power as well as +5 VDC computer power all of which is passed to the card via the A/D card. Where the ±12 VDC computer power is noisy and/or marginally low, a variant of AIM-16 called AIM-16P may be used. AIM-16P contains an on-board DC-DC converter that operates from +5 VDC computer power and provides isolated ±15 VDC for use by analog circuits on the card. This variant can be specified for all versions of AIM-16: e.g., AIM-16IP, AIM-16RP, etc. AIM-16 is particularly valuable in REMOTE ACCES systems because it can be used to condition low-level signals at the remote site and wiring that carries those signals can be kept short to minimize chances for noise pollution. One or two AIM-16P’s can be used with Model RAG128 in a RIDACS system as described in the REMOTE ACCES section of this web site.
CD provided with AD12-8 and RAG128 contains utility software to facilitate system integration of the two cards. Programs on the disk include illustrated board setup instructions, calibration procedures, linearization routines for commonly used thermocouple types and RTD’s, and sample programs demonstrating how to make the AIM-16/AD12-8 combination work in a system.