Data Acquisition

This flexibility allows stand-alone logger/controllers to be operated in a number ofways, depending on the required location, volume of data to be stored and availability ofpower:• Stand-alone operation with periodic data recovery (and programming whererequired) using memory cards or a portable laptop PC• On line to a host PC with periodic uploading of data (and programming whererequired)• On line to a host PC via modem, with periodic uploading of data (andprogramming where required), initiated by either the host PC or the remotedeviceWhere an application requires many more sensors than can be provided by a singlestand-alone controller, and these are distributed over a large area, a distributedlogger/controller network may be required. Each mode of operation, employing only asingle logger/controller, is also applicable when more devices are connected as part of adistributed network.The credit card size portable memory card provides a reliable media for transporting dataand programs, but requires a memory card interface connected to the RS-232 serial portof the computer. This is shown in Figure 7.1.Stand-alonelogger / controllerRemote Data LoggerThermocouples Strain gauges RelaysPCMCIACardComputerMemory Card InterfaceFigure 7.1Using memory cards to program and log data from a stand-alone logger/controllerProgramming the operation of a logger/controller and recovering data using thePCMCIA card is especially useful when the logger/controller is remotely located and/ornot connected to a host PC. Even when connected to a host PC, the storage capacity of thelogger/controller can be greatly increased by leaving the PCMCIA card permanently