Control/Signal Cable Length Requirement for Gas Turbine

[ppmsb]

Hi,

Was informed by the vendor that there is a max of 300 m cable length requirement from transmitter sensor to terminal point at rack room.

Any similar experience?

Thanks

ppm

 

[ScottyUK]

How far were you expecting? 2000 meters? 2 miles? 50 miles? 300m sounds entirely reasonable, perhaps generous even.


----------------------------------

Sometimes I only open my mouth to swap feet...

 

[ppmsb]

I'm expecting more than 300m. In our situation this makes lots of difference coz we need to install field auxilliary room (FAR) if need to comply with the 300m requirement. Based on the actual site survey we need about 400m.

 

[rmw]

I once had a vendor that had a 50 ft. maximum permissable length between transmitter and sensor. Their standard was based on their assumption that the cable would be run in a tray with other kinds of nasty (noisy) types of cables. I regularly ran their device 500-1000 ft. distance. But, I had to take precautions regarding shielding, wire sizing and not using trays that contained "nasty" actors.

rmw

 

[ScottyUK]

If the vendor says 300m then you should stick with it unless you can get a written dispensation from the manufacturer. Any problems with the instrument, whether related to the cable run or not, will be a cause of contention with the client because they are not installed in accordance with the manufacturer's specification. there'll be no warranty either. If these instruments form part of a safety system or have the ability to cause danger through their failure then you are leaving yourself wide open to a lawsuit.


----------------------------------

Sometimes I only open my mouth to swap feet...

 

[abeltio]

Beware of the 300m cable length, it means 300m of CABLE and not 300m between the unit and the rack room.

This is a typical requirement for field instrumentation and the ONLY one that can waive that requirement is the OEM, preferably: in writing.

Can this requirement be waived?
Well... it all depends on the application, if it is a thermocouple... almost certainly not, you are dealing with millivolts.
If it is a 4-20mA signal, maybe... provided that proper shielding and segregation from other voltage levels is approved by the OEM.
If it is a digital signal, 24VDC and above, probably yes.


saludos.
a.

 

[ppmsb]

Yu are right abeltio, 300m cable lenth requirement doesn't mean the distance between the unit and the rack room. It is from the sensor at site to terminal point at the rack room.

As informed by the OEM, there's no "negotiation" for thermocouple. But for other application, they are willing to give +5% allowance i.e. 315m.

Regarding digital signal, do yu have any experience using fieldbus foundation for the GE machine?

ppm

 

[abeltio]

No i do not have any experience with foundation fieldbus, that is a new development (GE-Fanuc, found with google)

saludos.
a.