Thank you! I will be more specific.
I work with instrumentation projects, sometimes the client is the Petrobras. There is one Petrobras standard that says “Instrument cables have to be connected in junction boxes, segregated by signal and by level tension” (Os cabos provenientes dos instrumentos de campo deverão convergir para caixas de junção, segregadas por tipo de sinal e nível de tensão). Only this!
But I have one situation in my hands where the instrument cables (analogical and digital) are connected in the same junction box. The manufacturer provided your skid with the instrument cables connected as mentioned above. In the skid there are 6 pumps. Each pump sends temperature and pressure signals (analogical 4~20mA) to your junction box. But in each junction box there are 3 digital signals too. They are: start, stop and Local/Remote for the pump. All signals leave the junction box in the same multicable. But, in my opinion, this is a special case, because the digital signals will never create interference on the analogical signals.
If the pump is stop, to start or to select L/R won’t create interference, because the pump is off. If the pump is on, to stop or to select L/R could create one interference, but not significant. If I press stop, the interference doesn’t matter, because the pump will stop and the analogical signals will stop to be send. Select L/R isn’t a command that will be done constantly, so it wouldn’t create a significant interference on the analogical signal.
But Petrobras want to change the connection, based in your standard.
I’d like to know which international standad shows it in detail.
All signals are 24Vcc. The multicable has individual and overall shield. All pairs are twisted.
Tky
