Pit valve controls

Why not run a fibre cable INSIDE the pipe? - of course, you'd still have to get it out somehow. But if there is a tapping point for eg pessure you might be able to use a compression fitting and get a good seal seal

- I'm not a fibre guru so could be totally out to lunch >Following on from John Shaw's thread, a client of ours who runs a large

Cameron If the piping configuration is amenable, you might be able to use pressure pulses to communicate. You could "talk" digitally, or modulate the pulses at different frequencies for different commands. There are some obvious limitations (and probably a bunch of not obvious ones), but in a situation like control of valves off of a common header it might work. However I don't know of anyone who provides a "package" solution like this.

Good Luck

Pat

If you have an energy source going to the pit, then you could transmit over those power wires to a more convenient location. The control signals would be on top of the power. There are some devices which do this for networking computers throughout a house.

Alternatively, if the pipes are metal, could you simply transmit your signals over the pipes themselves? As long as you didn't create a spark inside the pipe you'd be ok. My guess is that the current capabilities of a pipe are fairly significant compared to normal wire.

An interesting idea, Bruce, and thanks for thinking "outside the box".

The pipeline is large enough to cope with bending radii and such, but is pressurised to >10bar. I've found that it's easy to crush the fibre if you tighten the glands up too much and I'm not convinced that you could devise a fitting to get through the pipe wall without losing too much product.. The other thing is I don't know if you can get fibre sheaths that are petrochemical-resistant (most aren't).

Thanks! I hadn't noticed that before. I usually get bored before I get to the Appendix ;-)

Cameron:-)

Yep, with careful tuning this might work. Does anyone know of a company making sonar comms links that are intrinsically-safe??

Cameron:-)

Unfortunately we can't get cabling to the pits. I am thinking of using a small solar panel embedded in the pit lid to drive the instrumentation and an air reservoir for the valve operation.

A nice idea, but the pipes are buried, wrapped and cathodically protected. I'm not sure the signal would get very far.. I'll check.

Cameron:-)

Thanks. I had a look at the Westlock Controls site but couldn't find anything really special.. Is there anything specific you had in mind?

Cameron:-)

Even if it is cathode protected, you might be able to get something of an fm signal over the pipe. Using air pressure might be possible as a valve power source. If you could get a small fitting to the surface, you could stop by with a truck mounted compressor and charge it from time to time.

I think the fact that we are discussing on a newsgroup severely curtails the patentability of them.

Michael

Hokay.. does anyone know who might make such a device (one that exists outside of a University thesis) in quantity?? Having to be Class 1 Zone 1 approved limits the range of options signficantly, but doesn't mean there isn't some gadget out there that could do this..

Yep. That's exactly how I was going to do it - complete with a low pressure switch to tell the operator to come and top it up.

Bummer.. The drawing board is getting a little cluttered ;-)

Thanks, guys!

Cameron:-)

Do you have any idea how much resistance and signal attenuation there would be from one end of the pipe to the other? Could this be measured easily? If there isn't much, you might find that some common equipment with a wire bonded to the pipes would do it. The equipment for using power lines is apparently reasonably available.

Michael

Another thought, Cameron.

Since these pits are below ground, is there any storm-water drainage that you might be able to use to get an electrical connection into the pits?

Bruce.

Camer>Following on from John Shaw's thread, a client of ours who runs a large

Cameron,

The signal you would use would be an AC signal impressed on top of the DC used for cathodic protection. A simple capacitor is all you need to isolate the two. This techniques is universally used to separate DC bias from AC signal in practically every electronic device ever made. It would not be hard to measure so long as all your measurements are made at some higher frequency. I would guess that a 1 kHz beep would work very well. Connect a simple signal generator to you pipe via a capacitor and a resistor in series. Measure the voltage to the pipe and the voltage across the resistor. The ratio gives you your impedance. As long as it is high enough you are OK. That means there is no significant signal loss. If you can now pick up the beep with any simple head phone at other places in the system, you have a working signal system via the pipes. Just to repeat, the cathodic protections systems ensures that this will work. If you didn't have it the signal would short out through the ground.

Walter.

I hadn't thought of that.. Unfortunately, since the pits might contain jet fuel, they aren't piped anywhere but are pumped out every so often by a waste truck. It's amazing how little rainwater gets into them when it does rain - only an inch or so. Otherwise, yes that would have worked!

Thanks, Cameron:-)

Thanks, Walter. I'll have a look into this and see how far I get. I still wish there was something 'off-the-shelf' though..

Cameron:-)

Thanks, Jason. I look forward to hearing about it..

Cameron:-)

Cameron Dorrough wrote: [snip: jet fuel, runways, communications]

I have a customer who uses sound tones to control a remote pumping station, transmitted via the pipes. It's a big installation - I'll have an ask around how they do it.

Jason

Hi Cameron

Just a thought, Why not use laser or infrared beams (like TV remote Control). You might have problem when the path is interrupted by a plan but otherwise I don't see why this wont work.

Hi Akheel. Yes, there is the interruption problem that you mention, but the biggest one is that you need to get some structure above the pit level to transmit to and (like the radio option) this would get run over by the next aircraft to come that way.

I am still looking into the pipe transmission option (since this is the least intrusive), but the best one at this stage seems to be to slot the rubberised mastic fill *between* the slabs and direct bury a thin comms cable in that. If the cable is armoured (it would have to be anyway) it should be plenty able to handle the thermal compression forces. I am waiting for the client to comment.

Cameron:-)