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Abnormal Condition Review

What Are They 

Abnormal conditions are any condition that is contrary to the normal operation of the equipment.

Examples:

Solenoid valve not making its open limit.

Instrument flow is below its minimum limit.

Source Vessel is Empty

How To Configure 

Abnormal conditions are typically configured on the objects class or type.  However, the EM process conditions has two custom conditions that may be configured at the instance level.

All conditions are initially configured at the Class/Type level with exception to the two EM process custom conditions.  Conditions configured on the Class/Type are group based conditions in that they apply to all objects of a specific group.  For example:  CM is in Operator Mode applies to all CMs acquired by an EM.

Conditions may be configured at an instance level by making exceptions.

How to Trigger 

Most conditions have default programming that automatically trigger the condition.  All conditions that apply to a single object or custom conditions may be triggered programmatically.   Each of these conditions have an override tag and a trigger tag associated with them.   Setting the override defeats the default programming.  Setting the trigger triggers the condition regardless of the default programming.  You can use the trigger without the override if you just want to supplement the default program.   You don’t need to set the override for custom conditions since they have no default programming except for the two EM process custom conditions which have the configurable expressions.

Considerations 

The default configuration setup in the initial S88 Builder is for a very conservative system.  Where most any condition will trip or prevent operation.   This is typically not what the customer wants.  Most customers prefer a fault tolerant system with high up-time.  However, it is safer to trip as a default until each condition is evaluated by the developer.

  1. Start at the default level and consider what is the majority severity and action for each of the listed conditions for this customer.
  2. At each class consider the same but for that specific class and set those.
  3. Do the same at each type.
  4. On an individual bases consider if an instance requires special needs.   If there are several instances with that need then consider putting them into a new type.  However, if there are only 1 or two instances or the condition is specific to a sub-group of items then use the instance based configurations.

Propagation 

How are abnormal conditions propagated?

  • Every object has abnormal conditions starting at the lowest level: Instruments, CMs, Vessels, EMs, Units, Process.
  • An abnormal condition at a lower level can trigger an alarm and an action.
    Ex: CM monitors High Discharge pressure which trips the pump.
    Instrument monitors extreme high temperature and sets fault and alarm.
  • An abnormal condition may be independently recognized at multiple levels.
    Ex: Process Condition monitors High Discharge pressure which sets an Alarm and also trips the pump.
    EM monitors Extreme High Temperature alarm and Trips itself.
  • The action triggered by an abnormal condition may be recognized as an abnormal condition at a higher level.
    Ex: EM monitors the pump CM has tripped.
    EM monitors its associated instrument has a high fault and faults itself too.

A process condition faulting an instrument may also cause an abnormal condition in the instrument that it has been tripped due to a process condition.

Abnormal Conditions Consideration 

Big question: Should I set the alarm and action in the instrument or in the EM or in the Process?

This has 2 parts Alarm and Action

Alarm 

Alarming has no action but simply puts an alarm in the alarm summary.

There are 4 alarm severity options:

  1. None – Don’t alarm
  2. Info – Same as none
  3. Warning – Display in alarm log as a warning alarm
  4. Critical – Display in alarm log as a critical alarm

When considering at what level to add the alarm you must consider when the alarm is relevant.

For example:  Low Discharge pressure –

  • Setting this up on the instrument would cause an alarm even when the pump isn’t running (unless you configure the instrument to ignore low limit when not in use but then you need to inform the instrument when it is in-use).
  • Setting it up on the EM would miss the condition when an operator is running the pump manually.
  • Setting it up as a process condition allows for fine tuning controls of precisely when the alarm is armed and triggered but requires the most configuration and overhead. (The instrument can also monitor this process condition if it is the target of the condition)

At first glance it would appear the best place to alarm is in the instrument configured only while in use.  You should also set the In-Use delay to prevent it triggering too soon.  But you must also be sure to notify when the instrument is in use.  All instruments added to an EM will be considered In-Use while the EM is running.  However, this doesn’t work for when the user is running the pump manually.  So this solution doesn’t help any more than putting it in the EM.   You could programmatically set the instrument as in use by either setting the {instr}.c.Prg.Acquire or .Share tag or by adding the CM ID to the .Prg.InUseBy array.

After careful consideration, the best place to set this up is in the process conditions.   Here, the pump running for a short delay would arm the condition and the instrument low limit would trigger it.

Action 

The action is what the system should do as a result of the condition.

Possible actions are:

  Description Process3 Unit EM Vessel CM Instr
None No action X n/a X n/a X X
Alert Alert only1 X   X   X X
Perm Prevent starting/activating X   X   X  
Suspend Suspend EM X   X      
Hold Hold EM – Preferred over trip X   X      
Fault Same as perm but sets fault bit X   X   X X
Trip Trips device2 X   X   X X
Trip Oper Trip CM even in operator mode X       X  
Trip Local Trip EM only (don’t trip phase) X   X      
Trip Receive Vessel – Trip on receiving X          
Trip Send Vessel – Trip on sending X          

1All actions, other than none, cause an alert.  The alert action alerts only.

2Instruments can’t trip so this just sets up the recommended action for any high system monitoring it.

3Process condition actions depend on the selected process condition target.

The action is typically configured where the alarm is but may be configured at multiple levels:

  • Configuring the action at the instrument just sets up a recommended or monitorable condition because an instrument cannot take action.  Ex: setting a fault will trigger an instrument fault action in an EM or Process condition.  In this case I would setup a fault action to flash the alert color on the instrument and to enable the fault condition on the EM. (I don’t remember if the alarm also triggers an alert color regardless)
  • Configure the EM to monitor for the Low Suction instrument fault to trigger an Alert action because no need to fault to trip the EM. (since this is likely not the only instrument you would need to setup a instance based exception for this particular instrument if a different fault action is desired from other instruments).
  • Could also configure the Process Condition to cause an Alert action on the EM but that would be redundant if also configured in the EM.

 

 

Updated on December 6, 2018

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