Engineering Manual o.. - HVAC.Amickracing

MICROPROCESSOR-BASED/DDC FUNDAMENTALSPROGRAMMING CATEGORIESProgramming of microcomputer-based controllers can besubdivided into four discrete categories:1. Configuration programming.2. System initialization programming.3. Data file programming.4. Custom control programming.Some controllers require all four levels of program entry whileother controllers, used for standardized applications, requirefewer levels.CONFIGURATION PROGRAMMINGConfiguration programming consists of selecting whichpreprogrammed control sequence to use. It requires the selectionof hardware and/or software packages to match the applicationrequirements. Configuration programming can be as simple asselecting a specific controller model that matches the specificapplication requirements, or it can require keyboard selectionof the proper software options in a more complex controller.Universal type controllers, typically applied as zone-levelcontrollers for VAV or other terminal units, are usuallypreprogrammed with several control sequences resident inmemory. In these cases, configuration programming requiresselecting the proper control sequence to match the applicationthrough device strapping or keyboard code entry.SYSTEM INITIALIZATION PROGRAMMINGSystem initialization programming consists of enteringappropriate startup values using a keypad or a keyboard. Startupdata parameters include setpoint, throttling range, gain, resettime, time of day, occupancy time, and night setbacktemperature. These data are equivalent to the settings on amechanical control system, but there are usually more itemsbecause of the added functionality of the digital control system.System-level controllers are variable-function and are moreuniversal in application. These controllers must be able toperform a wide variety of control sequences with a broad rangeof sensor input types and control output signals. System-levelcontrollers require more extensive data file programming. Forthe controller to properly process input data, for example, itmust know if the point type is analog or digital. If the point isanalog, the controller must know the sensor type, the range,whether or not the input value is linear, whether or not alarmlimits are assigned, what the high and low alarm limit valuesare if limits are assigned, and if there is a lockout point. SeeTable 2. If the point is digital, the controller must know itsnormal state (open or closed), whether the given state is analarm state or merely a status condition, and whether or not thecondition triggers an event-initiated program.Table 2. Typical Data File for Analog Input.Point AddressUser AddressPoint typeRegular or calculationSensor Platinum (0 to 100F)Physical terminal assigned 16Use codeCold deck dry bulbEngineering unitFDecimal places for display XXX.XHigh limit 70.0Low limit 40.0Alarm lockout pointPoint descriptorAlarm priorityPoint addressCold deck temperatureCriticalCUSTOM CONTROL PROGRAMMINGCustom control programming is the most involvedprogramming category. Custom control programming requiresa step-by-step procedure that closely resembles standardcomputer programming. A macro view of the basic tasks isshown in Figure 13.DATA FILE PROGRAMMINGData file programming may or may not be required dependingon whether the controller is a fixed-function or variable-functiondevice. Zone-level controllers are typically fixed function sincethe applications and control sequences are generallystandardized. In these controllers, the input terminals arededicated to a specific sensor type and range, and the outputterminals are dedicated to a control relay or specific type ofactuator. The need for data files is minimized. The processoralways knows what to look for as it scans those points, and itknows how to process the data.ENGINEERING MANUAL OF AUTOMATIC CONTROL135