Features Displayed on Screen (HI520 display shown) Control Modes The control mode can be congured to be On/O¨, Proportional, or PID. The mode can be set high or low. High control mode is required if the process value is too high and needs to be decreased. Low control mode is required if the process value is too low and needs to be increased. For On/O¨ control, the hysteresis band is adjustable, while in Proportional and PID modes, deviation, control period, and other tuning parameters can be set to optimize control around a set point. For HI520, each channel can run control independently or sequentially. Hold Function During calibration, cleaning, and conguration the controller automatically goes into Hold mode. During Hold mode all control loops related are disabled. The analog outputs may be congured to go to a xed value or remain at the last value. The Hold function can also be triggered manually, using an external digital input or by entering in Manual mode. This is useful for disabling control when performing maintenance. Auto-Cleaning Cycle Di³cult applications often require an almost continuous maintenance of the probe. Processes with high-suspended solids, fats, oils, pigments, and microorganisms will coat the pH sensing glass, ORP sensors, and the reference junction. The cleaning function allows programming of one or more wash cycles and uses the relays to activate valves, pumps or compressed air based on the type of washing that is required to maintain probes for reliable results. Congurable Alarm System The alarm system is congurable for measured parameters. The alarm can also be activated by event triggers, set points, or abnormal operation. For example, if a dosing relay remains closed for an excessive period of time or if temperature exceeds an upper limit during an exothermic neutralization reaction. A blinking red LED signals an alarm state. All relays congured for control are inactivated until the alarm state is resolved. On HI520 use channel conguration to setup and trigger an alarm. LCD Information Local visual indicators of measurement details as well as errors are displayed. The ? DIAG key provides details of the issue. ? DIAG - Help and Diagnostic Key The help and diagnostic key (? DIAG) provides information related to errors; or in setup mode, information about settings. 15 Process Instrumentation 15.49 www.hannainst.com | controllers
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