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Thread: Locating with a lower frequency on deep water mains

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    Default Locating with a lower frequency on deep water mains

    I was wondering how well lower frequencies are able to locate water mains that range in depth from 5' to 15'. I currently use an older RD transmitter that only has 8K and 33K signals-both of which give me about a 1000' of signal before reciever readings become distorted (no matter how well I am grounded). I have heard that lower frequencies - <1K - not only travel further but are also less prone to bleeding off onto other lines and I was wondering how well these signals work on deeper pipelines. I locate water pipelines ranging from 12" to 90" diameter- ductile, steel, and concrete- and am getting ready to spec out a newer transmitter/receiver and was hoping to get some feedback on how well lower frequencies work for my application. Thanks for any help.

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    Moderator Goldenboy's Avatar
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    Default Re: Locating with a lower frequency on deep water mains

    I located water for about 4 years and all I can say is good luck with the low frequencies. I never got the low frequencies to work on water mains. When I had an RD I always used 65 because even 33 seemed not powerful enough. I think the main problem is all the fittings,valves, and other insulated fittings on the watermains make the lower frequencies nearly impossible. The high frequencies "jump" all the fittings.

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    Conservative Meanie ifinditunderground's Avatar
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    Default Re: Locating with a lower frequency on deep water mains

    It has less to do with the actual frequency, and way more to do with the wattage of the transmitter.
    GB you are right about higher frequencies jumping insulation and joints, but I have found that 8 and
    9.8 are extremely effective at locating shallow and deep water mains. But you have to have a
    Transmitter that puts out a minimum of 3 watts to be really effective. Also, the larger the pipe is,
    You must have a higher output transmitter to counter the massive amount of signal loss you will have
    The larger the pipes get. OP, if you are getting 1,000 feet out of a single connection point you are doing
    Very very well, especially on pipes greater than 36". Spec out a Metrotech 9890XT - 3 watts or an i5000
    -Up to 10 watts.
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    Default Re: Locating with a lower frequency on deep water mains

    I find it & GB,

    Thanks for the info. While a 1000' is good for most locates, the problem I am having is lack of hook-up points. The system I am locating is not a typical municipal system (with hydrants and services) and there are times when I have a full 1/2 mile between points in which to hook up to- which is not good in cases where the locate calls for miles instead of feet. Anyhow, I have rotated between induction and conduction-making sure the marks meet- to get the job done and had not had the chance to use lower frequencies. Honestly, I did not think lower frequencies would work well in my situation but I had to ask. I will look into the higher wattage transmitters (I wonder if these would be more prone to bleed over?) in my next locator purchase. Thank you both for your input as I am newer to the field and appreciate any and all information I can get.

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    Member Utilitrack's Avatar
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    Default Re: Locating with a lower frequency on deep water mains

    I assume that you are not having much luck locating cement or Asbestos Cement, A/C water lines with any type of EM locators (unless they have trace wire?). GPR would be best for those, though I have used an instrument called a Vibrocator, which uses vibration to "sound out" the A/C pipe for short distance under ideal conditions, but you need hydrants to hook the Vibrocator transmitter too, and sometimes thet break the older hydrants.

    I regards to deeper, larger ductile, cast or steel mains, the other poster are correct- you probably are running on a one watt transmitter from an old RD400? Most new instruments today start at 3 watts and go up from there, you should look at a 5 watt minimum, probably 10 watt.

    One alternative would be to contact Seektech, they made the "Q" ring transmitter that was an induction machine, the transmitter had programmable frequencies so you could probably use your existing receiver.

    Good Luck

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