Today is...
Thursday, July 20, 2017
Welcome to, the global online
community of automation professionals.
Featured Video...
Featured Video
A demonstration of EtherCAT control of linear motors using the CTC EtherCAT master.
Our Advertisers
Help keep our servers running...
Patronize our advertisers!
Visit our Post Archive
Questions about logic signal LTRUE in MARK V <I> controls

We have a 6B machine with MARK V <I> controls. The signal LTRUE on longname.dat is defined as "Always TRUE logic signal". Is there ever a point where this changes state other than loss of power?


There should NEVER be a coil for LTRUE (or LFALSE). If someone added a rund and a coil for LTRUE (or LFALSE), then there can be very, Very, VERY VERY serious and debilitating problems in sequencing.

The operating system is where LTRUE (and LFALSE) are "written to" and the OS tells LTRUE to always be true (a logic "1") and LFALSE to be false (a logic "0"). NO and NC contacts for both signals can be used in sequencing, but there should never be a coil for either of them. A NO LTRUE contact will always be closed, and a NC LTRUE contact will always be open. A NO LFALSE contact will always be open, and a NC LFALSE will always be closed. This is true as long as there is no LTRUE or LFALSE coil in the CSP.

Hope this helps!

By 6bturbinectech on 20 April, 2017 - 7:34 am

Thanks for the response. I did not want to imply that there was a LTRUE coil. It is a contact used to pick up a coil in our normal/standby 480v power to our TCC or PECC as some refer to it. The coil it is energizing is L3X2 which is defined as "Exciter Power Supply Selection". Confused us at first.

Thanks again.


I did not mean to imply that you implied there was an LTRUE coil. I have been to three sites where someone inserted an LTRUE (or LFALSE) coil in sequencing (because they believed the lack of one (or the other) was causing problems, or to try to change the operation of one LTRUE or LFALSE contact in the entire CSP). And, then the proverbial poop really hit the fan.

Basically the two signals are a way for GE to write generic logic/sequencing that would use a maximum number of signals/permissives and when those particular signals are not used on a particular job they can substitute with an LTRUE (or LFALSE) to enable or block some rung/function.

The initial CSP for any Mark V job was generated automatically from a program called BOBCAT (don't ask what it stands for). And it's BOBCAT--generally--that substituted LTRUE (or LFALSE) for some signal(s) that were not present in sequencing. Basically, the contacts (NO (Normally Open) or NC (Normally Closed)) are placeholders, and by using LTRUE or LFALSE they can keep the contacts in the rung without supplying a signal driven by an input or output or other logic. It's kind of unique method--except when people who don't understand the purpose try to "fix" things because of the absence of an LTRUE or LFALSE coil....

When you asked if there was ever a time when LTRUE was not true, well, that sounded like someone might have tried to drive an LTRUE coil with some logic in sequencing--usually to try to make on single LTRUE contact open or close, without fully understanding what happens to all subsequent occurrences of LTRUE in the CSP. And, it's usually because they believe that a single LTRUE contact is causing something to happen or not happen they perceive should be not happening or happening, respectively, and don't understand what happens to all other occurrences of LTRUE.

I may be complicating things even more, but, it's really just used to close or open NO or NC contacts when some signal isn't present or not used in a particular site's CSP. LFALSE is always false (logic "0").

You said "...It is a contact used to pick up a coil ...." Is that contact NO (normally open) or NC (normally closed)? If the contact is NO, then it will be closed at all times (because LTRUE is always a logic "1"). If it is NC, then it will be open at all times--because LTRUE is always a logic "1". (I presume the contact is NO because you say it's being used to pick up a coil, and the contact would have to be closed to pick up the coil if it's being driven by LTRUE.)

Hope this helps!

By Amar DAMENE on 20 April, 2017 - 5:07 am
0 out of 1 members thought this post was helpful...

Dear 6bturbinetech,

On your GT 6B with MARK V <I> controls, You will find more LTRUE on sequencing programs.

On longname.dat file, it is defined as "Always TRUE logic signal".

It means that this signal is always exist as:

Any signal of transmitter (4-20 mA)

The transmitter of pressure is always exist, then we have to consider it as LTRUE. only when power supply is out.....

Your request: Is there ever a point where this changes state other than loss of power? ....................I never saw.

Hope this guide you...