> Can you provide a link to the comment so I can build on the information for the explanation?

CSA,

It's from the forum "Getting a better understanding of gas turbine control" and the link is http://www.control.com/thread/1399292917.
Comment Posted on 18 May, 2014 - 12:46 pm.

 

> I don't think we know when 30SG-1 changes state, actually.

This may help, from the manual. Note the ignitor box has both NO and NC contacts for 30SG-1:

The exciter contains a diagnostic circuit that operates each time the exciter is operated (each time exciter is in the "ON" condition). The diagnostics circuit has no effect on the operation of the exciter. The diagnostic circuit monitors the exciter operation for these two things:

1-Output Voltage for a "minimum" value of approximately 15 KV

2-Spark Rate for a "minimum" value of approximately 1.0 sparks/second.


If the Output Voltage or the Spark Rate becomes less than the "minimum" value, a relay in the diagnostic circuit is energized and will stay energized for the remaining time the exciter is in the "ON" condition — the relay is de-energized when input power is removed from the exciter (when exciter is in the "OFF" condition).

The relay is connected to three terminals of the "Diagnostic Output" terminal strip, but does not send an electrical signal to those terminals. To have an indication that an exciter malfunction has occurred, an external circuit (supplied by the operator) must be connected to the "Diagnostic Output" terminal strip. When the relay is energized, a circuit between a pair of "normally open" terminals is changed to closed, and a circuit between a pair of "normally closed" terminals is changed to open.

 

Batman,

I have a better thread (not forum--control.com is the forum, which has individual threads (questions)):

http://www.control.com/thread/1026245600#1026245640

Try this and see if it's helpful or not. (I <b>HOPE</b> it is!)

And to your comment about not helping a stranger, we're all strangers until we meet--even if it's in a World Wide Web/Internet forum, AND I'm not just helping you. Hopefully I'm helping many others--not just now, but later, as others find and read the thread and responses.

As I've said before, I was extremely fortunate to have had a "stranger" (as he was in the beginning) help me many, many years ago when I didn't know a compressor bleed valve from a purge solenoid from a false start drain valve from an LVDT (heck--I couldn't even spell LVDT then!), and so I'm just paying it back, and also trying to "pay it forward" to some extent in the hopes that others will learn and be able to do the same with other "strangers" in their lives.

I'm not sharing any proprietary information, and none of this stuff is the "rocket science" it's made out to be. A lot of if is really simple--if people will just take the time to RTFM (Read The Fine Manual) and do a little bit of Internet research. I do realize that in some parts of the work Internet access is restricted, but I find in those same parts of the world that there is (UNFORTUNATELY!!!) a LOT of copyrighted material illegally posted to the World Wide Web/Internet so information is available, just not in more easily accessible locations. (I <b>AM NOT</b> encouraging anyone to ever download copy-righted material that has been posted illegally posted somewhere. Not ever. Never. I'm just saying that it's pretty hypocritical to block access to some sites and permit access--even encourage, as I've seen in some cases--use of sites that have illegally posted copyrighted material available for download. And that's all I'm going to say on this subject--information is out there, if one is patient and creative and ambitious.)

Anyway, have a read of the thread above--and my upcoming post to this thread--and see if it all begins to make sense. Actually, I recommend you read them several times over a couple of days, maybe longer, before asking for any clarification. It's a LOT of information, but hopefully presented in a clear and (intended) concise way, while being as literal as possible (considering all the possibilities and detailing them to make everything as clear as possible).

Together, after reading the two threads (more than once), you should be able to understand the reason for inversion masking, even if, technically, it's not really required in today's digital world of automation controllers. It's still a very useful concept to grasp--open to alarm/trip; closed on good/normal. And, I've been to MANY plants all over the world (industrialized, first-world countries as well as non-industrialized second- and third-world countries) where BAD things have happened when 'open to alarm/trip; closed on good'normal' hasn't been used/followed consistently in the plant design and commissioning.

One doesn't technically need inversion masking, it's just makes some things simpler (once certain decisions have been made, and continued through the decades even when control automation systems have changed). It's just one way of accomplishing something that could be done another way--but, as in most parts of the capitalistic world: if it ain't broke, don't fix it. Changing it in the GE world would entail a LOT of changes to a LOT of drawings and application code--and, again, if it ain't broke, why fix it? (But they should be much better at explaining it, shouldn't they? Because even their field service personnel and in many cases their control design personnel don't know or understand this stuff. And that means they can't explain it to anyone else, either.)

And, I always encourage everyone to do this when encountering something new or unusual: Draw things in a manner that makes sense to them while trying to work out and understand them. Sometimes, a drawing from a manufacturer can seem very obtuse and confusing, and just re-drawing it in a manner that you're comfortable with can be very enlightening. Once you see it in a familiar format, it will make sense in it's "native" format, too.

Use logic diagrams and tables as you work through things and issues--they can be very helpful and useful.

Remember: "Learning is finding out what you already knew." (Richard Bach, 'Illusions') And it is, isn't it? When somebody explains something so that you (finally) understand it, or when you finally come to know that you understand something, doesn't it feel like, "Hey! That makes sense! I knew that!!!" And we all do, it's just finding the way to, using our experience and points of reference, have it make sense with what we already know--and then it really is just like we knew this, we just didn't know we knew it.

I really enjoy seeing that "light" come on for people when they finally realize, "Hey! That's it! I knew this, and now I know I know it!" The expression on someone's face when they have that realization is absolutely priceless--even if I can't see their face!

As a former colleague was fond of saying, "This ain't rocket science!" And it's really not. But until one takes the time to research and understand--and to question things they're told and review and analyze them to see if they're logical and true--a lot of this stuff seems like rocket science.

 

be_anon,

Thanks for the information!

So, the diagnostic <i>circuit</i> operates each time the exciter (the ignitor power supply) is energized (so when l2tvx1 is a logic "1"). And a <i>relay</i> in the diagnostic circuit operates when there is a fault (low output or low spark rate). Hmmm.... (That brings up more questions about the alarm text message, but that's for another day.)

So, in this case, 30SG-1 changes state when 95SG-1 is energized <b>AND</b> there <b>IS</b> a fault.

As with the other "big" response earlier, I have read and re-read and re-re-read and re-re-re-read the post to find errors. Again, I hope the Kind, Friendly Moderator would accept a request to fix any errors should they rear their ugly heads after it is posted. (Thanks in advance!)

Batman,

Let's take the case of the 30SG-1/l30sg1 discrete input circuit being wired to the normally open (NO) contact of the ignitor exciter diagnostic circuit. Here's our drawing of a non-inverted input circuit:<pre>
NORMAL (Non-Inverted) NO 30SG-1 Discrete Input
to Digital Speedtronic Turbine Control Panel
(30SG-1 Changes State (Closes) on a Fault)

Hardware | Software
-------- | --------
|
Physical |
Contact |
30SG-1 Input Screw l30sg1
---| |----------o------------------( )---
|
| l30sg1
| ---|/|---</pre>
And here's the alarm rung from Batman's post above:<pre>
l30sg1 l2tvx1 L30SG1_ALM
---|/|--------| |-----------( )</pre>
And here's a table of what happens when l2tvx1 is energized and there <b>is NOT</b> a fault in the ignitor exciter:<pre>
NORMAL (Non-Inverted) NO 30SG-1 Discrete Input
to Digital Speedtronic Turbine Control Panel
(30SG-1 Changes State (Closes) on a Fault)

l2tvx1 30SG-1 NO l30sg1 Coil L30sg1 NC L30SG1_ALM
State Contact State Logic State Contact State State
------ ------------- ----------- ------------- ----------
"0" OPEN "0" (False) CLOSED "0"
"1" OPEN "0" (False) CLOSED "1" - <b>ALARM!!!</b></pre>
In this case, l30sg1 is a logic "0" when there is not a fault. Because the NC l30sg1 contacts in the alarm rung would be closed when there is not a fault this would mean that every time the ignitors were energized and there <b>was NOT</b> a fault that the Mark VIe would annunciate an alarm--erroneously. (Oh no, Mr. Bill!!!)

And here's a table of what happens when l2tvx1 is energized and there <b>IS</b> a fault in the ignitor exciter:<pre>
NORMAL (Non-Inverted) NO 30SG-1 Discrete Input
to Digital Speedtronic Turbine Control Panel
(30SG-1 Changes State (Closes) on a Fault)

l2tvx1 30SG-1 NO l30sg1 Coil L30sg1 NC L30SG1_ALM
State Contact State Logic State Contact State State
------ ------------- ----------- ------------- ----------
"0" OPEN "0" (False) CLOSED "0"
"1" CLOSED "1" (False) OPEN "1" - NO alarm</pre>
In this case, l30sg1 is a logic "1" when there is a fault. This would also mean that if the ignitors were energized and there <b>WAS</b> an alarm that the alarm <b>would NOT</b> be annunciated (because the NC l30sg1 contact in the alarm rung would be open). Both conditions are <b>BAD</b>--an alarm when there is NOT a fault, and no alarm when there IS a fault.

Now, let's see what would happen if someone just inverted the 30SG-1 input (l30sg1) to the Mark VI, while leaving the circuit connected to the NO contact of 30SG-1:<pre>
INVERTED NO 30SG-1 Discrete Input
to Digital Speedtronic Turbine Control Panel
(30SG-1 Changes State (Closes) on a Fault)

Hardware | Software
-------- | --------
|
Physical |
Contact |
30SG-1 Input Screw l30sg1
---| |----------o------------------(<b>I</b>)---
|
| l30sg1
| ---|/|---</pre>
And here's the alarm rung from Batman's post above:<pre>
l30sg1 l2tvx1 L30SG1_ALM
---|/|--------| |-----------( )</pre>
And here's a table of what happens when l2tvx1 is energized and there <b>is NOT</b> a fault in the ignitor exciter when the 30SG-1 (l30sg1) discrete input is inverted:<pre>
INVERTED NO 30SG-1 Discrete Input
to Digital Speedtronic Turbine Control Panel
(30SG-1 Changes State (Closes) on a Fault)

l2tvx1 30SG-1 NO l30sg1 Coil L30sg1 NC L30SG1_ALM
State Contact State Logic State Contact State State
------ ------------- ----------- ------------- ----------
"0" OPEN "1" (True) OPEN "0"
"1" OPEN "1" (True) OPEN "0" - NO Alarm</pre>
In this case, l30sg1 is a logic "1" when there is not a fault--and there would not be an alarm when there was not a fault when the ignitor exciter was energized because the NC l30sg1 contact in the alarm rung would be open--and this is as it should be.

And here's a table of what happens when l2tvx1 is energized and there <b>IS</b> a fault in the ignitor exciter when the 30SG-1 (l30sg1) discrete input is inverted:<pre>
INVERTED NO 30SG-1 Discrete Input
to Digital Speedtronic Turbine Control Panel
(30SG-1 Changes State (Closes) on a Fault)

l2tvx1 30SG-1 NO l30sg1 Coil L30sg1 NC L30SG1_ALM
State Contact State Logic State Contact State State
------ ------------- ----------- ------------- ----------
"0" OPEN "1" (True) OPEN "0"
"1" CLOSED "0" (False) CLOSED "1" - <b>ALARM!!!</b></pre>
In this case if there was a fault when the ignitor exciter was energized, l30sg1 would be a logic "0" and the NC contacts of l30sg1 could be closed and there <b>WOULD BE</b> an alarm. (All is good, Mr. Bill!)

<b>NOW,</b> let's consider what would happen if a wire fell off a terminal in the 30SG-1 circuit that was connected to an inverted input, or a wire came out of a crimp terminal lug, or a wire came loose from the Mark VIe input terminal board for the 30SG-1 discrete input--<b>AND</b> there was a fault when the ignitor exciter was energized, then even if the NO contact of 30SG-1 closed the Mark VIe would not see the change of state--and there would be NO alarm when there was a fault. So, this is not a good thing--and is a "violation" of GE's policy of an open circuit to alarm or trip and a closed circuit when the condition being monitored is good/normal.

All too often, unfortunately, people just simply change the inversion mask to make an input "work"--but it's not really working properly, meaning that it would not alarm if there was an open in the circuit. Sure, there's no alarm when there's no fault, but what about when there is a fault and there is an open in the circuit and the contact closure doesn't get to the Mark VIe? Then there is no alarm--and that's not really "working properly." In this case, the ignitor exciter, it's not really too much of a problem because this isn't used as turbine trip or shutdown condition. But, it could make troubleshooting difficult if the turbine were having difficulties starting that were a result of problems with the ignitor exciter that weren't alarmed because of a open in the input circuit.

So, how to fix this and ensure that an open in the circuit would not prevent a fault from being recognized by the Mark VIe? Change the wire at 30SG-1 from the NO contact to the NC contact <b>AND</b> use a non-inverted input.

So, here's all the requisite drawings and tables for a NC contact from 30SG-1 connected to a non-inverted input driving l30sg1:<pre>
NORMAL (Non-Inverted) 30SG-1 NC Discrete Input
to Digital Speedtronic Turbine Control Panel
(30SG-1 Changes State (Opens) on a Fault)

Hardware | Software
-------- | --------
|
Physical |
Contact |
30SG-1 Input Screw l30sg1
---<b>|/|</b>----------o------------------( )---
|
| l30sg1
| ---|/|---</pre>
And here's the alarm rung from Batman's post above:<pre>
l30sg1 l2tvx1 L30SG1_ALM
---|/|--------| |-----------( )</pre>
And here's a table of what happens when l2tvx1 is energized and there <b>is NOT</b> a fault in the ignitor exciter:<pre>
NORMAL (Non-Inverted) 30SG-1 NC Discrete Input
to Digital Speedtronic Turbine Control Panel
(30SG-1 Changes State (Opens) on a Fault)

l2tvx1 30SG-1 NO l30sg1 Coil L30sg1 NC L30SG1_ALM
State Contact State Logic State Contact State State
------ ------------- ----------- ------------- ----------
"0" CLOSED "1" (True) OPEN "0"
"1" CLOSED "1" (True) OPEN "0" - NO Alarm</pre>
In this case, l30sg1 is a logic "1" when there is not a fault, and the l30sg1 NC contact in the alarm rung would be open so there would be no alarm. This is good, right? When the ignitor exciter is energized and there IS NOT a fault, there will NOT be an alarm.

And here's a table of what happens when l2tvx1 is energized and there <b>IS</b> a fault in the ignitor exciter:<pre>
NORMAL (Non-Inverted) 30SG-1 NC Discrete Input
to Digital Speedtronic Turbine Control Panel
(30SG-1 Changes State (Opens) on a Fault)

l2tvx1 30SG-1 NO l30sg1 Coil L30sg1 NC L30SG1_ALM
State Contact State Logic State Contact State State
------ ------------- ----------- ------------- ----------
"0" CLOSED "1" (True) OPEN "0"
"1" OPEN "0" (False) CLOSED "1" - <b>ALARM!</b></pre>
In this case, l30sg1 would be a logic "0" when there was a fault, and because the l30sg1 contact in the alarm rung would be closed there would be an alarm. This would also mean that if the ignitors were energized and there <b>WAS</b> a fault that the alarm <b>WOULD BE</b> annunciated. This is good! This is what we want.

It would also mean that if a wire came loose (fell off) in the 30SG-1 circuit connected to the NC contact that when the ignitor exciter was energized that an alarm would be annunciated--which may be "false", but it alerts the operator and technician to a problem with the wiring (see more on this below). And this is good, too.

Right?

Well, almost.... By GE's convention, the discrete input coil is <b><i>usually</b></i> a logic "1" when there is an alarm or trip condition, and in the above scenario with a NC 30SG-1 contact driving a non-inverted discrete input l30sg1, it (l30sg1) is a logic "1" when there is NOT a fault. And, the '30' in the signal name stands for "Alarm Device", which implies that when the signal is a logic "1" it should indicate an alarm (or trip) condition. Right?

Well, to make everything match GE's conventions for 'closed circuit to indicate good/normal conditions; open circuit to indicate alarm/trip condition' <b>AND</b> the discrete input signal should be a logic "1" to indicate an alarm or trip condition <b>AND</b> match the signal naming convention (in this case, a 30 device is an alarm device--implying that when the signal l30sg1 is a logic "1" it's indicating a fault with "spark generator #1" (95SG-1)), we have to invert the input <b>AND</b> change the sense of the contact in the L30SG1_ALM rung, like below:<pre>
NC 30SG-1 Connected to an INVERTED Discrete Input
of a Digital Speedtronic Turbine Control Panel
(30SG-1 Changes State (opens) on a Fault)

Hardware | Software
-------- | --------
|
Physical |
Contact |
30SG-1 Input Screw l30sg1
---<b>|/|</b>----------o------------------(I)---
|
| l30sg1
| ---| |---</pre>And here's the <b>modified</b> alarm rung from Batman's post above:<pre>
l30sg1 l2tvx1 L30SG1_ALM
---<b>| |</b>--------| |-----------( )</pre>
And here's a table of what happens when l2tvx1 is energized and there <b>is NOT</b> a fault in the ignitor exciter:<pre>
NC 30SG-1 Connected to an INVERTED Discrete Input
of a Digital Speedtronic Turbine Control Panel
(30SG-1 Changes State (opens) on a Fault)

l2tvx1 30SG-1 NC l30sg1 Coil L30sg1 <b>NO</b> L30SG1_ALM
State Contact State Logic State Contact State State
------ ------------- ----------- ------------- ----------
"0" CLOSED "0" (False) OPEN "0"
"1" CLOSED "0" (False) OPEN "0" - NO Alarm</pre>
When the ignitor exciter is energized and there IS NOT a fault, there will NOT be an alarm. And when there is NOT a fault, l30sg1 will be a logic "0".

And here's a table of what happens when l2tvx1 is energized and there <b>IS</b> a fault in the ignitor exciter:<pre>
NC 30SG-1 Connected to an INVERTED Discrete Input
of a Digital Speedtronic Turbine Control Panel
(30SG-1 Changes State (opens) on a Fault)

l2tvx1 30SG-1 NC l30sg1 Coil L30sg1 <b>NO</b> L30SG1_ALM
State Contact State Logic State Contact State State
------ ------------- ----------- ------------- ----------
"0" CLOSED "0" (False) OPEN "0"
"1" OPEN "1" (True) CLOSED "1" - <b>ALARM!</b></pre>
When there is a fault, 30SG-1 NC contact will open, l30SG1 will be a logic "1", the NO contact of l30sg1 will be closed--and there <b>WILL BE</b> an alarm. All is good!!!

Now, if a wire falls off in the 30SG-1 circuit or comes loose from 30SG-1 or the Mark VIe 30SG-1 input circuit, then immediately l30sg1 will go to a logic "1", and as soon as the l2tvx1 goes to a logic "1" to energize the ignitor exciter a fault will be annunciated--even if there is not a fault at the exciter (the NC contact remained closed)! Which will send the technician out to troubleshoot the problem--which will be very easy to troubleshoot.

Let's say during a START, the alarm 'IGNITOR EXCITER CHANNEL FAILED' was annunciated but the turbine started and was subsequently loaded. That would mean that at least one of the ignitor exciter outputs (presuming it has two outputs) and/or one of the ignitors fired and ignited flame in one of the combustors. The application code only energizes the ignitors for a short period (30-60 seconds, at most) so l2tvx1 will go back to a logic "0" after the firing timer expires and the ignitor exciter will be de-energized. Which should mean that the 30SG-1 NC contact would again close, so the technician should be able to use ToolboxST to look at l30sg1 and find it a logic "0"--meaning that there was no fault when the ignitor exciter was de-energized. BUT, he finds l30sg1 a logic "1" when the ignitor exciter was not energized--indicating that either:

1) 30SG-1 is not working properly and the NC contact is "stuck" open

or

2) there is an open wire/termination somewhere in the 30SG-1 discrete input circuit

or

3) there is a problem with the 30SG-1 discrete input circuit of the Mark VIe (either the input terminal board has a problem, or the I/O pack circuitry for that input has a problem)--<b>BUT</b> in this case the Mark VIe would most likely be (SHOULD BE) annunciating a Diagnostic Alarm for this particular input circuit, so an alert technician should be able to quickly diagnose the problem as a Mark VIe problem because of the Diagnostic Alarm.

Using his trusty voltmeter, the technician measures the voltage at the 30SG-1 discrete input terminals and finds ~130 VDC, indicating an open circuit. He then uses the drawings provided with the unit to check all the terminations in all the junction boxes out to the ignitor exciter junction box and ultimately he finds a wire has come loose from a crimp terminal in the ignitor exciter junction box. He repairs the crimp (carefully--because it will have ~65 VDC on the wire while the turbine is running!) and when he checks l30sg1 again using ToolboxST he finds it is now a logic "0" when the turbine is running. (I would have gone immediately to the ignitor exciter junction box to look for a loose termination or crimp; and if I didn't find anything there I would follow the conduit leaving the ignitor exciter junction box with the 30CG-1 wires in it to the next junction box, opened that junction box and looked for loose wires/crimps, and so on until I found the problem. No need to find drawings--which may or may not have been marked-up to reflect changes during installation and commissioning.)

So, I think we've beat this subject to it's (hopeful) conclusion.

 

CSA,

Can't ask for more!! Thanks a lot for your help & guidance. I'll go through the link you provided, before asking questions. I regret what I said about helping strangers and yes, we are not strangers anymore!! I totally agree with your comment "This ain't rocket science". But sometimes it's very difficult to understand the nuances of an "alien" topic no matter how much effort you put into the subject unless some one guides you. Thank you once again & all those who share their knowledge on this forum.