maximum control cable length
maximum control cable length
(OP)
I need to regulate a flow control valve from a pressure transducer located 9 miles downstream. For safety reasons the client requires the communication is hard wired. I am advised that the length is too long to send a signal from the pressure transducer to the control valve via cable (hard wire).
What is the maximum length that we can send a signal by cable ? Can I provide an amplifier to boost the signal? Cost is important - how much am I looking at to send a hard wired analogue signal from a pressure transducer to a flow control valve over a length of 9 miles. ?.
What is the maximum length that we can send a signal by cable ? Can I provide an amplifier to boost the signal? Cost is important - how much am I looking at to send a hard wired analogue signal from a pressure transducer to a flow control valve over a length of 9 miles. ?.





RE: maximum control cable length
TTFN
RE: maximum control cable length
http://www.dataforth.com/catalog/pdf/Ldm70.pdf
According to the specs, this modem can be used to transmit data up to 12 miles using a twisted pair cable at up to 57.6K baud rate with hand shaking. I have not used one, but I am interested the application and found this device on the internet. I am sure there are others available as well. Hope this helps.
RE: maximum control cable length
I would suggest fiber optic or spread-spectrum radio. Maybe a dual-path / dual-radio setup?
I am in the Gas Industry and we have several critical measurements and controls via radio. Historic data is stored locally. PID control is also local, with setpoint coming from a remote location. Local instrument is powered by battery with photocell charger.
Then, there used to be several methods using telephonic communications (the old Bristol Metameter or FSK equipment). Perhaps they still make them? I wouldn't use repeaters on a 24VDC system - much more likely to fail.
Good luck!
RE: maximum control cable length
On the process side of things, it seems like there would be a long transport lag. How long do you think it will take for the valve position change to be felt at the pressure sensor?
xnuke
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: maximum control cable length
The available lag time between the valve change and the change at the pressure sensor can be several hours - (The pipe feeds into a tank with two days storage.
Perhaps a man and a bicycle are my best option?
Thanks again for the advice.
RE: maximum control cable length
There are several vendors you might talk to. Try www.scadalink.com or www.omnexcontrols.com (both Canadian companies), or search for "spread spectrum" on the Web.
RE: maximum control cable length
http://www.siservices.com/prod/Fiber_Modems/t1e1_fiber_modems.htm
http://www.rad-direct.com/static_fam_fiber_optic_modem.html
They all seem to support transmission distances well in excess of 9 km.
TTFN
RE: maximum control cable length
xnuke
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: maximum control cable length
put a second transmitter near the valve and wire it to your controller normally.