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How accurate are cameras?

  • 22-12-2011 12:17pm
    #1
    Juniorhurler
    Closed Accounts Posts: 1,363 ✭✭✭


    You all know the cameras I am talking about, with the solar panel attached on top. They are positioned at the entrance to speed limit zones. They are only there to advise you of your speed.

    The reason I ask is my speedo is registering a difference of 7km/hr with one that I pass every day. I presume it is my speedo needs calibrating even though I am on standard factory fitted wheels and original size tyres.


Comments

  • #2
    ironclaw
    Registered Users, Registered Users 2 Posts: 8,004 ✭✭✭ironclaw


    Juniorhurler wrote: »
    You all know the cameras I am talking about, with the solar panel attached on top. They are positioned at the entrance to speed limit zones. They are only there to advise you of your speed.

    The reason I ask is my speedo is registering a difference of 7km/hr with one that I pass every day. I presume it is my speedo needs calibrating even though I am on standard factory fitted wheels and original size tyres.

    They are not cameras

    They are not accurate at all. I'd say at a guess ±10km/h. They are radar based so they are heavily influenced by bounce, reflection, other cars etc etc. And they aren't calibrated very well.

    And your speedo will be out by about 3km/h or so depending on your speed i.e. Mine is about 3km/h at the low end, 10km/h at the high end. All speedo's read above your actual speed, how much depends on the manufacturer etc. You can get your speedo calibrated but really and truly it ain't worth it.


  • #3
    theteal
    Registered Users, Registered Users 2 Posts: 7,593 ✭✭✭theteal


    afaik, all in car speedos are purposely a little bit off to give you a bit of leeway


  • #4
    Juniorhurler
    Closed Accounts Posts: 1,363 ✭✭✭Juniorhurler


    ironclaw wrote: »
    They are not cameras

    They are not accurate at all. I'd say at a guess ±10km/h. They are radar based so they are heavily influenced by bounce, reflection, other cars etc etc. And they aren't calibrated very well.

    And your speedo will be out by about 3km/h or so depending on your speed i.e. Mine is about 3km/h at the low end, 10km/h at the high end. All speedo's read above your actual speed, how much depends on the manufacturer etc. You can get your speedo calibrated but really and truly it ain't worth it.

    Ya sorry I didn't know how they work. All electronics are like some type of voodoo magic to me.
    Thanks for the info though.


  • #5
    bazz26
    Registered Users, Registered Users 2 Posts: 51,363 ✭✭✭✭bazz26


    GPS is the most accurate for measuing your speed so if you have a portible SAT NAV, compare it against the speed sign's measurement.


  • #6
    kirving
    Registered Users, Registered Users 2 Posts: 6,129 ✭✭✭kirving


    Those boards are pretty accurate as far as I've seen. Exactly the same reading as GPS on a number of occasions.

    Measuring the frequency of a reflected signal isn't that complicated, even with other cars and reflections etc. ±10km/h is quite a bit off. 5-10% off measured speed maybe. A handheld radar can get a speed from over 1000m if I'm not mistaken, and that couild be used in court.

    Dont some of those systems use wire embedded in the road?


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  • #7
    ironclaw
    Registered Users, Registered Users 2 Posts: 8,004 ✭✭✭ironclaw


    Kevin Irving wrote: »
    Those boards are pretty accurate as far as I've seen. Exactly the same reading as GPS on a number of occasions.

    Measuring the frequency of a reflected signal isn't that complicated, even with other cars and reflections etc. ±10km/h is quite a bit off. 5-10% off measured speed maybe. A handheld radar can get a speed from over 1000m if I'm not mistaken, and that couild be used in court.

    Dont some of those systems use wire embedded in the road?

    Your talking about Radar, Laser and GATSO all at the same time. They are all different!

    Radar can't do 1000m. Laser can.

    Wire systems are available but not in Ireland.


  • #8
    coylemj
    Registered Users, Registered Users 2 Posts: 25,624 ✭✭✭✭coylemj


    Kevin Irving wrote: »
    Those boards are pretty accurate as far as I've seen. Exactly the same reading as GPS on a number of occasions.

    The ones near me are spot on, they agree with the GPS every time. I wouldn't make any assumptions unless you have a GPS which shows that the one near you is well off the real speed.

    OP, have you changed tyre size and could that have affected the accuracy of your speedo?


  • #9
    Juniorhurler
    Closed Accounts Posts: 1,363 ✭✭✭Juniorhurler


    coylemj wrote: »
    The ones near me are spot on, they agree with the GPS every time. I wouldn't make any assumptions unless you have a GPS which shows that the one near you is well off the real speed.

    OP, have you changed tyre size and could that have affected the accuracy of your speedo?

    No, original size tyres. I must check it with a sat nav and report back.


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