Applies To:
  • CitectSCADA 1.00 1.01 1.10 1.11 1.20 2.00 2.01

Question: How fast is scanning of high resolution alarms compared to normal alarms? 

The Citect Alarm Server scans High resolution alarms at the same rate as normal alarms. The difference with High resolution alarms is that when the alarm is tripped the Alarm server will read the alarm trip time from the PLC. You must place code in the PLC to store the trip time of the alarm into registers so that the Alarm server can read this time and evaluate the exact time the alarm was tripped and sort the alarms in the correct order.

The alarm server scans the alarms as fast as it can read the data out of the PLCs (and as set by the parameter [ALARM]ScanTime). However under some conditions you may want the alarms trip times and sequence to a higher resolution. High Resolution Alarms were designed as the limit on the alarm scanning is restricted by the communications to the PLCs and this cannot be increased. So the High Resolution Alarms are not scanned faster than the normal alarms, however they allow you to get a more precise indications of the trip times and sequences.

High resolution alarms a processed in the following way.

1). The alarm server reads all the data from the I/O Devices associated with the triggers for the alarms.

2). When the data has been returned from the I/O Devices each high resolution alarm is checked to see if the trigger has just become active. If the alarm has just become active the alarm server will request to read the time stamp register associated with this alarm.

3). When all the time stamp registers have been read the alarm server will save each time stamp to the associated alarm (adjusting its ONTIME) and then sort all the newly triggered alarms in the order of the time stamps.

In version 3.0 and later High Resolution Alarms are renamed Time Stamped Alarms to give a clearer indication of what this feature does.