Systems Reference Library - All about the IBM 1130 Computing ...

Analog InputIndustry, science, research, government -- all arefaced with the need for collecting increasing amountsof data within decreasing time scales. Physicalmeasurements must be monitored and quantified withgreater speed and accuracy than ever before. Thecollection of analog data and its conversion for presentationto the digital processor-controller (P-C)are the functions of the analog input features.A physical phenomenon is first sensed andconverted to an analog electrical signal by sensorsor transducers, such as thermocouples or straingages. Electrical signals from sensors or transducersmay be in the millivolt, volt, or milliampererange. Low voltage signals (less than 1 volt) areamplified to a level acceptable for conversion todigital form. All customer lines from transducersare terminated at the control system on screw-downterminals. The signals are also conditioned at theterminals, including the filtering of extraneoussignals, known as noise.Conversion of analog signals from a voltagelevel to digital information is accomplished by ananalog-to-digital converter (ADC). Such convertersare complex enough to permit analog signals frommultiple sources to be converted by sharing oneADC. The necessary switching is accomplished bya multiplexer.The data path from sensor or transducer tothe P-C is shown in Figure 30.ANALOG INPUT UNITS AND FEATURESThe analog input units and features provide modularpackaged equipment used to convert voltage or currentsignals to digital values. The modules used toaccomplish the conversions include analog-to-digitalconverters, multiplexers, amplifiers, and othersignal conditioning equipment.The units and features that accomplish the analoginput function are briefly introduced below, followedby more detailed descriptions. A descriptionof the operation of analog input and its relation to theP-C is given later in the "Programmed ControlModes" section.As shown in Figure 31, input signals are routedthrough termination, signal conditioning elements,multiplexer switches, an amplifier (low level signalsonly), and into the ADC. The output of the ADCis presented to the P-C via data channel or directprogram control operations.1851 MULTIPLEXER TERMINAL, MODEL 1: Thisis a modular chassis that is mounted in an 1828 Enclosure.It provides up to 64 analog input multiplexerpoints (two-wire), with signal conditioning elementsfor each point. The chassis houses either solid statemultiplexers or relay multiplexers. When relaymultiplexers are installed, up to two differentialamplifiers can be mounted in each terminal.I> 0'1> I)DigitalTerminationSignalConditioningElementsMultiplexer117207A1Figure 30. Analog Input Data PathAnalog Input 91