Are SCADA System Events Chronological?

Normally yes, so that the plant facilities staff can trace back the history leading up to any incident.

What you want is a Sequence Of Event -SOE- recorder function in your SCADA.

That function is usually native in these systems but it might be merged with other 'pages/views': event page or alarm page.

On these two other views the chronological order might be a specific filter you have to apply i.e. if the Operator makes a search based on another filter, the view may no longer show the SOE view.

Patrice

AND gate

The AND gate is an electronic circuit that gives a high output (1) only if all its inputs are high. A dot (.) is used to show the AND operation i.e. A.B. Bear in mind that this dot is sometimes omitted i.e. AB ---------------------------------------------------------------------------- to understand the solution, let us understand the function of a simple AND gate. above the doted line ,the symbol of AND gate with two inputs is shown. when both the inputs are logic 1, then only we get logic 1 at output AB. let us take another similar AND gate.feed the output of first gate to one of the input of second gate. the other input of second gate is available to us to control the output of second gate.if there is a logic 1 on this control input, we shall get some output at the output terminal of second gate . this may be logic 0 or logic 1 as per the result of AB. such arrangement is called LOGIC GATE WITH OUTPUT ENABLED. SCADA master is connected to all RTU(S) in parrallel for signal direction from master to RTU(S), but the ouputs of all RTU(S) have some logic circuit similar to OUTPUT ENABLED GATE and then connected to master in parrallel. thus when master polls all the RTU(S) with a code of a particular RTU, all the RTU(S) get this code, but only that RTU for which the code pertains, is allowed to be connected to master by these OUTPUT ENABLED GATES and this is the only RTU, which is allowed to transmit its signal to master. turn by turn, master keeps on polling and turn by turn, the RTU(S) keep on responding. the question of collision does not arise with the controll of these OUTPUT ENBLED GATES. it is all automatic and 100 % sure. THANKS.

Thanx qajendrasingh01, we are using plcs as RTUs,these RTUs working as output enabled gates am not so clear about it, fine you said a polled RTU will be the only to transmit to the master but take a case when it is polled and it takes time to respond (fine its given some time to respond and if it dosn't respond with in that period it's rendered in-operative and polled again later) as it may not be having data to transmit, and i believe the master keeps on polling all the RTUs. Your explanation has made me understand the system config, but most SCADA system are equiped with CSMA/CD and to you may be sure that data collision does not exist but i believe it dose. We don't have SOE, what about a data time stamp? can that be of help?

Qajendrasingh01 i have liked you explanation.

Thanks.

dear waco, i m thankful to u for taking interest to understand my explanation and being quite frank. let me further ellaborate. imagine there are five rooms numbered 1,2,3,4.5. candidates for some interview are sitting in all these five rooms. each room is guarded by guard. in another big room, a person is sitting to take the interview.in the first round eight candidates from each room are called. if thr are no guards,all these canidates shall rush up.here thr is simlle. the interviewer is equivalent to the master of scada and each room is a rtu. five rtu(s) in all.interviewer asks the first gurd to send eight candidates. only the first guard opens the door for eight candidates. all the remaining four rooms are closed for this time.then interviewer asks the guards turn by turn and the interview is conducted in a systematic way.the guard or the door is equivalent to the switch i termed as output enabled gates, openning one at a time as per the code issued by master. second point, in the example, every time only 8 canidates are being called. u may say each rtu in turn is replying with 8 bits. something like that. third point, this output enabled switch is playing magic. if these switches are removed, in most likelihood, collision shall occur and events shall not reach in succseetion.without these magic switches, the LAN shall work on CSMA/CD basis. thanks

Thanks for the explanations, however here are some tuorials that may be useful about PLCs ,PLC5's and SLC500's

http://www.youtube.com/RonBeaufort

Thanks.

hi !

From my experience in SCADA systems, I think I can clarify the issue.

Only hughe SCADA systems use what is called sequence of events. To accomplish this all the system design has to keep in mind that every sample down to transmitter has to have a time stamp attached. This is not particularly difficult in SCADA systems having large database records attached to eah point, one of them being the time stamp and quality qualifier of the data.

Other issue is the protocol used for data aquisicition, you may need to use time tag aware protocols, such as DNP3 or any IEC870 variations, that can transmit the time of the measurement along the data, over the comm channel.

Finally the data adquisitor must attach a syncronized timestamp to the data, which leads us to clock sync, which may be done using remote syncronization from the SCADA system, in less stringent applications and local high precision clock ( atomic, gps, gprs sync ), and margiinally taking into account time zones, in really nation wude systems.

If a system, uses this techniques, all the events can be collated by the real time occurence of the event and not for the arrival time of the message packets.

I hope this info may be usefull to you.

if you need more detailed info, you can reache me at carlfeld@gmx.net