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Thread: Vivax accuracy question

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    Default Vivax accuracy question

    Vivax accuracy question

    I had the opportunity to stop by a site and see the excavation and exposed utilities.

    I had marked a 25 pair phone line between two apartment building, maybe 50' total. There were no external peds so hook up was only by ring clamp in one of the basements,. There was no readily available ground for direct connection. From the connection point it went to a dead end in the other building.

    The cable was about one foot deep and the marks were off by 12 inches. I have never had an 810 do this and I am puzzled about how the Vivax got so far off on a shallow cable with no other utiltiy nearby to distort the signal.

    I could see they would be digging right on the path of the cable and was careful and did not hurry. I did not pendulum swing the receiver and kept it parallel to the ground. The gain was not set high. Frequency was 8.19KHZ.

    There was a plastic duct on the ground carrying a temporary private electric service between the two buildings, the ticket was to bury a new and permanent service. There was no bleed over on this electric to compensate for. The marks were not off on the side where the temporary electric was, they marks were off in the other direction away from the electric.

    The marks were in tolerance for local call before you dig requirements but were beyond my personal requirements. I just have never been off on a shallow utility like this and cannot figure out how this happened.

    Anybody else run into this with a Vivax?

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    Mke
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    Default Re: Vivax accuracy question

    PL, were you dealing with any elevation changes? I am not sure if it affects the vivax or not, but I know some times when there is another utility that is above the lower antenna in the reciever that you may get a false lock. However, it wouldn't be consistant, and you would of noticed some inconsistancies with the signal. I have had one experience with some FAA comunication ducts. I ring clamped the copper in the vault, and when I got out 25' or so the signal tapered off of the utility. There were 2 empty conduits, One conduit filled with fiber, one filled with copper, and the FAA loves to run a Counterpoise withe their ducts, so 1/2" copper wire running with everything. My main signal was about 1' away from ducts. With "side boxing" I was able to pick up two additional tones (Copper and Counterpoise), but the main hookup gave me that false reading. The funny part was that Induction did not give me that false signal. =)

    You had to of been affected by the ground laid electrical....... but i'm not sure why.

    mke

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    Default Re: Vivax accuracy question

    Quote Originally Posted by Mke View Post
    PL, were you dealing with any elevation changes? I am not sure if it affects the vivax or not, but I know some times when there is another utility that is above the lower antenna in the reciever that you may get a false lock. However, it wouldn't be consistant, and you would of noticed some inconsistancies with the signal. I have had one experience with some FAA comunication ducts. I ring clamped the copper in the vault, and when I got out 25' or so the signal tapered off of the utility. There were 2 empty conduits, One conduit filled with fiber, one filled with copper, and the FAA loves to run a Counterpoise withe their ducts, so 1/2" copper wire running with everything. My main signal was about 1' away from ducts. With "side boxing" I was able to pick up two additional tones (Copper and Counterpoise), but the main hookup gave me that false reading. The funny part was that Induction did not give me that false signal. =)

    You had to of been affected by the ground laid electrical....... but i'm not sure why.

    mke
    The ground there was absolutely flat, no hillside to throw the signal off.

    The old buried electric would have been disconnected except perhaps for the neutral The dig showed the new electric installed in a shallow trench not as deep as the old electric but a little deeper than the existing phone in question. So there was no shallow utility throwing the signal off.

    If the above ground electric were to throw the signal off then the marks would have been closer to the above ground electric, here they were on the side of the phone opposite from the above ground electric.

    I have in the field used this Vivax and an 810 to check it's marks to see if the Viva was out of calibration. Both of their marks are dead on matches.

    I am completely puzzled by this.

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    Senior Member sprayandpray's Avatar
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    Default Re: Vivax accuracy question

    I couldn't explain this but it's nice to know that the 'equipment' can be off and therefore not always be the Locator's error.
    I might not be as good as I once was, but I'm as good once as I ever was !


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    Junior Member Linden Riddle's Avatar
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    Default Re: Vivax accuracy question

    Did you compare the peak reading to that of the null reading? What about the "compass" indicator--what did it show?

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    Default Re: Vivax accuracy question

    Quote Originally Posted by Linden Riddle View Post
    Did you compare the peak reading to that of the null reading? What about the "compass" indicator--what did it show?
    The directional indicator matched the path of the utility.

    I did not switch back and forth between peak and null modes, peak being my usual mode. There were no other signal to sort out and sift through as my utility and the abandoned and cut off private electric were the only things in the area so I just used peak mode.

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    Mke
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    Default Re: Vivax accuracy question

    hmmmm..... switching back to the 810? =)


    The only thing that I can think of, is that their is another utility that is pulling your signal, but with the 25pr being the closest to the surface, that one should be the dominant signal. was their any other signs in the basement of other utilities leaving the same wall the 25pr was? Did they uncover the Cut off cable? If not, could it of been where your paint was?

    This is where I don't envy you Public locators.... When you are tasked with locating A specific utility, you have only the authority to access that utility, and not enough time to sweep the whole area. If your signal puts you on a different utility, you won't know till they uncover it.

    when you have to locate everything, such as a private locator, your main goal is locating, and your second goal is to Identify when applicable. And you are able to use any means neccesary to locate. Induction and what have you.

    mke

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    Default Re: Vivax accuracy question

    Quote Originally Posted by Mke View Post
    hmmmm..... switching back to the 810? =)

    The only thing that I can think of, is that their is another utility that is pulling your signal, but with the 25pr being the closest to the surface, that one should be the dominant signal. was their any other signs in the basement of other utilities leaving the same wall the 25pr was? Did they uncover the Cut off cable? If not, could it of been where your paint was?

    This is where I don't envy you Public locators.... When you are tasked with locating A specific utility, you have only the authority to access that utility, and not enough time to sweep the whole area. If your signal puts you on a different utility, you won't know till they uncover it.

    when you have to locate everything, such as a private locator, your main goal is locating, and your second goal is to Identify when applicable. And you are able to use any means neccesary to locate. Induction and what have you.

    mke
    The abandoned electric was not uncovered and it may have been under where my mark was. But it had to have been open at both ends on the hot legs and maybe just the neutral connected. So then the neutral may have carried the signal. Still there was nothing around the phone in that basement where I clamped onto the cable, seems like any signal on that neutral would have been too weak to have pulled me off.

    At one time I was marking phone, gas, electric and TV which I liked. I had drawings for everything and sorting all the signals out resulted in a very accurate locate.

    Still if I had to I could hook up to another utility to sort out it's interfering signal, done it many times.

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    Default Re: Vivax accuracy question

    Quote Originally Posted by ProfessionalLocator View Post
    The ground there was absolutely flat, no hillside to throw the signal off.
    Ok, I'm a newb. Sorry if this is a dumb question, but why would a hillside throw a signal off?

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    Default Re: Vivax accuracy question

    Sorry, I should have re-read the first couple posts better. I have run into some confusing signals when tracing along next to abandoned wires that have faults in the insulation or casings. I'll shut up now and just try to learn something.

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    Default Re: Vivax accuracy question

    Quote Originally Posted by Inspired View Post
    Ok, I'm a newb. Sorry if this is a dumb question, but why would a hillside throw a signal off?
    A commo msitake ona hillside is to move th ereciver keeping it the smae distnace over the gorund. That is as you move the receiver down the hill you keep dropping the reciver as the earth drops down below it.

    You have to hold the receiver so that it is at the same level as you move it left and right. Otherwise you are changing the distance between the receiver and the signal resulting in a false high point reading. Also you can be changing the angle of the signal because as you move it from left to right you are not only closer to the signal source but are changing the angles of the signal.

    Hard to explain with just words. I always demonstrate this to a newb using a receiver.

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    Default Re: Vivax accuracy question

    I think I understand. You have to sweep side to side on a level plane rather then following the slope. If you follow the slope your mark will end up off to the side equal to the angle of the slope. Correct?

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    Default Re: Vivax accuracy question

    Quote Originally Posted by ProfessionalLocator View Post
    Vivax accuracy question

    I had the opportunity to stop by a site and see the excavation and exposed utilities.

    I had marked a 25 pair phone line between two apartment building, maybe 50' total. There were no external peds so hook up was only by ring clamp in one of the basements,. There was no readily available ground for direct connection. From the connection point it went to a dead end in the other building.

    The cable was about one foot deep and the marks were off by 12 inches. I have never had an 810 do this and I am puzzled about how the Vivax got so far off on a shallow cable with no other utiltiy nearby to distort the signal.

    I could see they would be digging right on the path of the cable and was careful and did not hurry. I did not pendulum swing the receiver and kept it parallel to the ground. The gain was not set high. Frequency was 8.19KHZ.

    There was a plastic duct on the ground carrying a temporary private electric service between the two buildings, the ticket was to bury a new and permanent service. There was no bleed over on this electric to compensate for. The marks were not off on the side where the temporary electric was, they marks were off in the other direction away from the electric.

    The marks were in tolerance for local call before you dig requirements but were beyond my personal requirements. I just have never been off on a shallow utility like this and cannot figure out how this happened.

    Anybody else run into this with a Vivax?


    You gotta use peak AND null for every locate. You would have got a different result with each and would have known you did not have a good locate. Same thing that asshole did to me today.

    PEAK Aaaaaaand NULL Every Time please.

    PS it doesn't matter what kind of machine you are using.

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    Default Re: Vivax accuracy question

    Quote Originally Posted by Cheddar View Post
    You gotta use peak AND null for every locate. You would have got a different result with each and would have known you did not have a good locate. Same thing that asshole did to me today.

    PEAK Aaaaaaand NULL Every Time please.

    PS it doesn't matter what kind of machine you are using.
    Completely agree, a receiver should always be set on peak and null together, it's quite clear the signal was not round and a higher frequency was required for the locate. Typically I never even use 8khz with a clamp unless my signal is bleeding in a highly congested area, 33khz is my first port of call for a clamp and if this cable is dead a higher frequency 65khz-131khz quite often is more effective. If all else fails I highly suggest investing in a Pipehorn 800 HL as they quite often can get you out of trouble.

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