Data Acquisition

• The source and level of interrupt signals generated. Interrupt signals can beprogrammed to occur at the end of a single conversion or a DMA block. Theconfiguration of the interrupt levels used is commonly selected by on-board links.• DMA control signals and the configuration of the DMA level(s) used. Theconfiguration of the DMA levels used is typically selected by on-board links.• Normal I/O to and from I/O address-locations on the board.• Wait state configuration for use in machines with high bus speeds or with nonstandardtiming. The number of wait states is usually configurable by on-boardlinks.As previously demonstrated, great care must be taken in the connection, earthing andshielding of signals, received from external transducers (or similar signal sources), to signalconditioning equipment. This is especially true where the signal levels are very small and/orthe signal sources are a long way from the measuring equipment. In these cases, the effects ofearth loops, induced noise, and common mode voltages can introduce errors that lead to largeinaccuracies in the signal measurement.The three basic configurations for connecting input signals to signal conditioningequipment are available on plug-in A/D boards:• Single ended• Pseudo differential• Differential5.3.1 Single ended inputsSingle ended inputs are those where the signal is transmitted over a single conductor andreferenced to analog ground AGND. The single conductor is connected to the HI terminal ofthe amplifier while the LO terminal of the amplifier is connected to AGND. This is shown inFigure 5.10.External signalsVHI 0CH 0VLO 0ES 1CH 1ES 2CH 2CH 3ES 0CH 4ES0+VCMCH 5CH 6CH 7AGNDCommon signal groundES 3ES 4ES 5ES 6ES 7CableHost input connectorInput MultiplexerES0+VCM+G-O VInput amplifierwith gain GG(ES0+V CM)AGND or OVSystem reference ground pointA/DDigitalCodeFigure 5.10Single ended inputs