Re: [PSUBS-MAILIST] Re: anymore--pressure test

[AndrePevestorf@aol.com]

In einer eMail vom 14.04.2002 05:56:24 (MEZ) - Mitteleurop. Sommerze schreibt DBACKIDS@aol.com:


> just rig up a finely-tined pressure guage inside with a radio transmitter. 


Do you believe that this will work from inside a steel hull??? (then I guess the hull itself has to work as antenna but then the antenna is directly connected to the water (the low potential) I´m not sure that this will work.

Radio controlled modelsubs can receive signals up to 1m or so... but then...

Why do not use simple wires??? You need anyhow a secure rope and a modern pressure indicator works with a "two-wire-technique " (so called in german)  You put in 12...42 Volt and get the actual pressure as a linear relationed signal between 4...20 mA. Thermal changes will be compensated automaticly and the resistance of the wire (the lenght) doesn´t care ...
Just measure the responding current and if  4mA was set to be equal 1 atm and the range was set to 1.2  atm (1.2 -1 = 0.2 bar range spreeded from 4 to 20 mA gives 0.2 / 16 = 0.0125 bar per mA)

If somebody wants a PDF data sheet of such a pressure indicator ... I have some in the office.

quick overview:

A absolute pressure indicator from ABB [AMD 210] price ~ 650 EURO (netto) 0...40 bar working field but can be set to any wished range. (electronic)
We use for our purposes (air pressure monitoring)  a customer range  0...1600 mbar (normal athmosphere = 1013,2 hPa or mbar) 

A differential pressure indicator [2010 TD] ~ 1500 EURO available for 10 /60 /400 mbar or 2,5 / 20 bar membrans ....

Normal steel allows mind. 2-4 % elastic deformation and if you proceed from the assumption that the hull shrinks more or less equal the max. allowed lost of volume could be calculated....

But if it is a wrong design than maybe only one part of the hull works like a drumhead and can reach the plastic area and could in the end fail due to reach the dead load ... but the expected decrease of volume was not reached until the hull became leak....

A.