Alarm (function block)

[WKla 0]

Hello, First of all I want to ask, if you have experience with this field, what is the general practice in SCADA systems: There is a computer that is the Master and a PLC that is the Slave. Where should the alarm limits be kept and the values of the alarms be calculated in the PLC or in the Computer? Each monitored value should have 4 alarm limits (LowLow, Low, High, HighHigh), 4 boolean for the inhibition of each of the alarms corresponding to the 4 limits and 4 boolean that are the alarms. Should I use only 2 alarm limits (Low and High)? Last, I want to build a FB to monitor a process value and to output the alarms for the 4 alarm limits. If you have other observations or advices I'm glad to hear them. Thank you.

[Gambit 326]

This is something most would do in the scada system. There you can easily define extra setting as deadband , deviation etc. for the alarms As an example here is a screencapture from Citect for the settings for an analog alarm. This will be similir to most scada systems Edited 5 Nov 2010 by Gambit

[WKla 0]

Hello, So I presume that the Delay (let's say the Low Delay) is a time interval. If the variable tag is below the Low limit for the Low Delay interval the Low Alarm is set? Or the Delay has the meaning of hysteresis? If the variable tag is below the Low limit the Low alarm is set, but is reset only after the variable tag is greater than (Low + Low Delay)? Obs: We build a SCADA system from scratch, we don't use Citect or other prebuilt scada systems How about the acknowledgment of the alarms? How this should work? Thank you.

[Gambit 326]

Alarms => check attachment What would you like to know about Acknowledgement? CitectSCADA.pdf Edited 5 Nov 2010 by Gambit

[WKla 0]

Thanks for explanations about alarm. About Acknowledgment, if an alarm occurs and operator acknowledges the alarm, but the condition of the alarm remains, how should the system react? Should the SCADA reactivate the alarm at an certain interval of time, or activate the alarm only after the condition alarm is ON again (after switching it OFF). I don't know if I made my self clear. Thank you.

[Gambit 326]

Normally you would have different alarmlists or colors for alarms indicating the status of the alarm The acknowledged Alarm should stay in the (current) alarmlist when still active but with a different color then unacknowledged alarms.

[Inntele 60]

Hi WKla, There is a firm rule: anything that directly affects the control process should be handled in the PLC, and only in the PLC ! SCADA no more than a human-machine interface. Even if there exists an appropriate alarm function, use this option only if the monitoring system is implemented. That is, the alarms must be processed in the controller, but a warnings if they do not affect to control process can be processed on the high level. Nevertheless, it is better to create all such flags in the PLC, and to use SCADA only as a means to display and store them (Alarm and Event lists), and for manual reset them in PLC.

[WKla 0]

Hello, So now we must decide which alarms are critical for the process and let the PLC handle it. For the moment I've put the project on pause, so I will eventually come back latter with other questions. Thank Gambit and Inntele.