api 551 1

[masoudinst]

I am in the middel of reading api 551, process measurement and instrumentation.there some unclear points I faced with.I needed some helps in this regard. For example in sec. 2.2.2 the last sentense is unclear.

 

[danw2]

The theme of 2.2.2, Transmission Practice, is the industry practice to measure at the process and then transmit that measurement electrically or pneumatically to the control room, so that the process medium being measured, hydrocarbons, is not piped into the control room.

The last sentence of the 1993 version reads, "Insulation and heating of long lines to prevent freezing are also minimized or eliminated by the use of transmission systems."

This refers to a side benefit of pneumatic/electrical measurment signaling because pneumatic/electric signaling does not require the costs and maintenance of insulation and heat trace that piping some hydrocarbons might require.