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6/12/2010 10:15 AM | |
Posts: 147 Rating: (34) |
Hi
The difference between them, is closely related to the actual nature of the signal the alarm is monitoring. Digital signals: Their state varies from "0" to "1", or logical FALSE to logical TRUE. Analog signals: These are an actual value, usually ranging from some number to another, e.g. -32768 to +32767, etc. So, coming now to answering your question. If you have a Discrete Alarm, you can only check if this signal turns "0" or "1". When this happens, then you get an alarm in your HMI. This could be e.g. if you press an Emergency Stop button. On the other hand, discrete alarms are monitoring a value and activate when this value goes above or below a certain (pretty much determined) limit. This limit could be a fixed value (a constant) or a value specified by the user (a variable - a tag in our terms). When your tag goes beyond this point, the alarm is activated. This could be e.g. a temperature going above a certain level. Directly quoting from the SIMATIC HMI WinCC flexible 2008 WinCC flexible 2008 Compact/ Standard/ Advanced manual:
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