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MARK VI Loop Test
Loop Testing MARK VI Speedtronic

Here is a quick tl/dr breakdown of my problem. This is the only information I have on a PM I am supposed to complete: SPEEDTRONIC CONTROL LOOP, TEST SMR-260. What am I supposed to do?

Here is the long story.

My plant is using a MS7001EA GE turbine with MARK VI TMR. I am the only I&C tech here and I don't know much about MARK VI.

Our PM software can be a bit light on the details on what is expected of us. The only clues I have as to what is expected of me is this blurb SPEEDTRONIC CONTROL LOOP, TEST SMR-260 and that it was last completed in 2015. I am looking for direction to develop a procedure on how to perform this test. Honestly, I have never done loop testing before either, which seems to be a software test(?).

I have been looking through our manuals, but we don't have any real maintenance standards on site. At least anything I think of as a maintenance standard. I am a bit fresh out of the Navy.

Any help would be greatly appreciated.



GE typically uses modified ANSI device numbers which are of the form 63QA-1, for example. 63 is a pressure switch, Q in the first place for GE-design heavy duty gas turbine refers to the L.O. system, the A in the second place refers to Alarm, and the -1 means it is first the low Lube Oil pressure sensing device (in a possible redundant configuration).

There is another device numbering system, KKS (Krappy Knumbering System, as it's affectionately referred to) which is not used very often in North America but is widely used in other parts of the world. It can be very subjective and a low L.O. pressure switch will NOT always have the same designation at different plants all using the same KKS device numbering "system" (hence, the Krappy designation).

A loop test, or loop check, involves testing the circuit of a particular input or output to be sure, first that the circuit is continuous, and second, that the loop is providing the proper indication(s) to the control system for conditions in the field (if it is an input to the control system), or that it is acting properly (if it is an output of the control system).

For example, let's say you want to perform a loop test/check for the device loop for 63QA-1. You would need to identify what the signal name in the control system is (in the case of GE-design heavy duty gas turbines that would usually be L63QA, or l63qa, depending on the vintage of the turbine control system) and then you would need to go to the pressure switch (usually mounted on the Accessory Gage Cabinet, sometimes mounted on the collector (non-drive end) of the generator, and cause the pressure switch to change state. (Pressure switches, and temperature switches and limit switches have contacts which are either open or closed depending on the magnitude of pressure or temperature or the position of some device.) In the case of 63QA-1 and L63QA, when the contacts of 63QA-1 are open the L.O. pressure is low, and when the contacts of 63QA-1 are closed when the pressure is good (normal). So, the contacts of 63QA-1 are closed when the pressure is normal, and open when the pressure is low--to provide an alarm to the operator and control system that the L.O. pressure is low.

In the Speedtronic turbine control system, L63QA (or l63qa) will be a logic "1" (true) when the L.O. pressure is low, and a logic "0" (false) when the L.O. pressure is normal.

So, if the unit is not running and is not on Cooldown, the contacts of 63QA-1 that are connected to the Speedtronic turbine control system will be open (because there is no L.O. pressure), and the value of signal L63QA (or l63qa) will be a logic "1". So you would need a jumper to simulate a closed contact while someone was observing the signal L63QA (or l63qa). When you jumpered the two wires at the pressure switch together signal L63QA (or l63qa) will change from "1" to "0"--and when you remove the jumper from the two contacts the signal L63QA (or l63qa) will change back to logic "1".

That's a loop test/check. You have verified that the loop from the Speedtronic turbine control system to the pressure switch and back from the pressure switch to the Speedtronic turbine control system is good--that the signal in the turbine control system changes state when the device's contacts "change state", AND you have also proven that the signal is getting the correct indication for when the L.O. pressure is low and when it's normal.

Most people don't understand that a loop test/check has to do two things: Prove the circuit to/from the device is continuous AND that the device provides the proper indication(s) when it should (in the case of an input), or that the device operates as it should (in the case of an output).

Now, you need to ask whomever wrote the PM or caused the PM to be given to you, what is SMR-260. I suspect it may be an output from the Speedtronic turbine control system to another control system (an input to the other control system), or that it's an output from another control system to an input of the Speedtronic turbine control system. In either case, it will have at least two wires, and it will be indicating the status of something or it will be changing state or value (if it's a 4-20 mA signal, for example). And you will need to work out how to "simulate" or measure or monitor the "device."

I wish I could tell you what SMR-260 is, and what it's purpose/function is. But, it's not something I have ever encountered--at least identified as SMR-260. Again, I would suspect it's something to do with another control system that is either providing an indication to the Speedtronic (and the Speedtronic has a similar or different signal name associated with the signal), or it's the Speedtronic providing some indication to another control system (and the Speedtronic has a similar or different signal name associated with the signal).

Now, when you find out what SMR-260 is and where it is and what it does, you need to "mark-up" the PM sheet so it can be modified in the software, or get the responsible person (usually there's someone on site who has the most knowledge/seniority on the PM software who has the task of maintaining the database) to add the appropriate description and information to the PM for that device.

I have described a loop test, or loop check. There is another function that I&C (or C&I) people perform--and that would be to use a calibrated pressure source connected to the pressure switch 63QA-1, for example, and then apply pressure to the switch and see that it changes state when the Device Summary (a document provided by the packager of the turbine, GE or whomever) says it should change state. 63QA-1 usually changes state when the discharge of the Main- or Auxiliary L.O. Pump drops below a certain value, say 50 psig. So, you would attach the pressure source to the pressure tap of 63QA-1 and slowly increase the pressure on the switch's diaphragm. As the pressure goes above, say 55-60 psig (all switches have some deadband, right), the switch contacts will change state, going from open to closed. And, you would record that pressure. Then you will slowly relieve the pressure on the switch and note when the contact goes open--it should be around 50 psig, in our example.

In this case, you are "calibrating" the pressure switch--really you are just verifying that the switch operates as specified. If the switch didn't change state at all (indicating it is broken and needs to be replaced), or if it changed states at different pressures than the turbine packager specified (indicating it needs to be re-adjusted to specification, if possible, or replaced if not possible to get it to work properly) you would note all of the information on the data sheet/PM for the device, to be input to the PM software for anyone who wants to know the last time the device was function-checked ("calibrated" as too many like to call it).

If you have a colleague, you should have that colleague watching the signal associated with the device on the HMI, in this case L63QA (or l63qa), to see that it changes state when the contacts of 63QA-1 change state, AND, that the indication is correct for the current condition. So, when there's zero pressure on 63QA-1, L63QA should be a logic "0"--indicating low L.O. pressure, and when the pressure is above the specific "reset" position (from the Device Summary) the signal indicates normal pressure. Monitoring the device's signal on the HMI is a great check to make sure the loop wiring is still good, and that the proper indications are being "received" by the Speedtronic turbine control system as the switch is operating. So, you've done several things at once--proved the device operates as and when it should, and that the loop to the Speedtronic turbine control system is good and is receiving and displaying the proper status indication.

Hope this helps! Please write back to let us know what you find. The GE-heavy duty gas turbine control community here at has been going strong for about 15 years, and there are LOTS of threads with LOTS of good information about Speedtronic (Mark*) turbine control systems and associated devices and systems here on available any time by using the 'Search' field on the Menu bar of every webpage. (It's recommended you use the Search 'Help' the first couple of times you try using the search function, as the syntax isn't like your preferred World Wide Web search engine--but it's fast.)

Lastly, "Feedback is the most important contribution!"(c) here at As you read many of the threads, you will find there is a LOT of feedback from the original poster letting others who read the threads (now, or in the future) if the information provided was helpful, or not. And that's what differentiates from many other similar sites--the feedback from the original poster, and even from others reading the posts, helps anyone reading the posts to know if the information provided was good and helpful, or not. It really is a credit to the community here that, for the most part, those asking for help or information provide feedback. It helps others who are or may be having the same or similar problem, and it also lets the responders know if the information provided (for free!) was helpful or not.

So, if you find the information helpful or useful--and if you can provide anything to help others who may be experiencing the same problem, please--do so by providing feedback. It's what makes the threads so useful--now, and many times in the future.

Welcome to the community!


>So, when
>there's zero pressure on 63QA-1, L63QA should be a logic
>"0"--indicating low L.O. pressure, ...

That should have read:

So, when there's zero pressure on 63QA-1, L63QA should be a logic
"1"--indicating low L.O. pressure, ...

Sorry for any confusion.

Thank you so much for you in depth reply. After some hunting and poking around, this is what I was able to determine: SMR-260 is the old PM database nomenclature and means nothing. What I have is a PM to perform a loop test for the entire Speedtronic system, which is a bit much for a single PM. I will have to look into breaking this down into multiple, smaller tests and go from there.

Thanks again!