<div dir="auto">Hello professionals,<div dir="auto"><br /></div>

Hello professionals,

Greetings of the day!!

I am working on projects where RIU(Remote interfacing Unit) are use.

While testing the communication I am facing a situation which I am unable to understand.

If my both network cable is removed from the RIU scanner then I am getting a not communicating Alan's on the alarm list and events.

But if I open PHV(process history View) of one of the AI module which is communicating from the same the RIO Iam getting a modbad alarm and my AI is holding up the last value.

As a result once the communication is restored back to normal then there bis no discontinuity in trend.

Shouldn't we have got do data there.!??

I really appreciate a response which will help us improving our understanding and concept.

U.G.

• 15 Dec 2020 9:35 AM
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1 Reply

• Andre Dicaire

  

  • 29 Jan 2021 4:41 PM

  The AI Block has set the BAD status indicating the value unsuitable for automatic control, but it also holds the last known value. Normal Function block behavior on a downstream PID would be to shed its mode to manual to prevent unwanted windup of the loop, all built in features.
  
  Status of values is an important feature of DeltaV, allowing your control modules to respond accordingly. Note that with DeltaV Continuous Historian, the Status of the signal is also captured and you can set the PHV trends to indicate when the value is BAD. The Status field is described in Books on line in greater detail.

  Andre Dicaire

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