Omega Owners Forum

Chat Area => General Discussion Area => Topic started by: Squatch on 13 March 2009, 14:29:51

Title: Plod calibrated speedo
Post by: Squatch on 13 March 2009, 14:29:51
Not of the highest importance - but good for pub topic..anyone know if the plod calibrated speedos are 100% accurate? Normal speedos give you an extra 5/10 mph..
Title: Re: Plod calibrated speedo
Post by: Sad on 13 March 2009, 14:33:22
I can't say that they're going to be 100% accurate, but when the cars are still in use by the force I imagine they'd need checking every 12months or so making them as accurate as possible...
Title: Re: Plod calibrated speedo
Post by: Radar on 13 March 2009, 14:39:25
I would say they would be right on the money - I got stopped once and question the accuracy and was shown a report which stated the speedo was tested for accuracy that very morning  :'(
Title: Re: Plod calibrated speedo
Post by: Sad on 13 March 2009, 14:40:06
Just found this:

'8.2.  Calibrated speedometers must be tested weekly, over a measured distance, and before the completion of a tour of duty during which any speeding offence is detected.'

from:
http://www.kent.police.uk/About%20Kent%20Police/policies/p/p04.html

Doesn't say how accurate they have to be though...

HTH...   :y
Title: Re: Plod calibrated speedo
Post by: Squatch on 13 March 2009, 14:49:29
Very interesting...thank you all. I remember some speedos that were atrocious - old Jags come to mind! And anything Italian...
Title: Re: Plod calibrated speedo
Post by: Sad on 13 March 2009, 14:55:35
When I've got the Tom Tom going in my Mig I'm surprised at how accurate the speedo is.  It's only about 3 or 4 mph out at 80, ahem, sorry 70    ::)
Title: Re: Plod calibrated speedo
Post by: Proz on 13 March 2009, 15:25:40
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When I've got the Tom Tom going in my Mig I'm surprised at how accurate the speedo is.  It's only about 3 or 4 mph out at 80, ahem, sorry 70    ::)

Im the same with the Navman  :y
Title: Re: Plod calibrated speedo
Post by: hotel21 on 13 March 2009, 15:34:46
Police calibrated speedos are certified accurate to less than 1% from IRS at Nottingham who pretty much have the UK market to themselves.

A standard speedo is required by legislation to be accurate to within 10% either + or -.  That said, 99.9% of them read high as it boosts the drivers ego sometimes to see a magic number on there - 100mph? - and the car is only actually doing 90....

Calibrated speedos are supposed to be checked at the start and the finish of a shift over a measured distance, just like any other piece of calibrated speed enforcement kit.  Allegedly.  Apparently.  Sometimes......
Title: Plod calibrated speedo
Post by: hotel21 on 13 March 2009, 15:39:01
[movedhere] Omega General Help [move by] hotel21.
Title: Re: Plod calibrated speedo
Post by: Kevin Wood on 13 March 2009, 15:46:30
Calibration of the speedo is one thing, of course, but wheels and tyres have an influence too. In fact, they are probably the biggest contributor to the uncertainty on an Omega because once you've got a signal from the wheel sensors it's just a matter of measuring frequency, which is easy to do to this level of accuracy.

Kevin
Title: Re: Plod calibrated speedo
Post by: hotel21 on 13 March 2009, 15:52:01
The initial calibration takes into account the rolling circumference/diameter of the wheels/tyres, assuming tyres are 'mid worn' through their tread depth, so I have been told.  That way, if brand new tyres are fitted to the car the speedo will read slow and vice versa when tyres are worn.

We used to get patrol car tyres changed at 3 to 3.5 mm which, when you think theres only about 7 or 8 mm max when new, would easily achieve the less than 1% certified.
Title: Re: Plod calibrated speedo
Post by: Andy B on 13 March 2009, 16:04:48
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.... to be accurate to within 10% either + or -.  .......

I thought it was +0% -10%  :-/   :-/
ie it could never read slower than actual road speed.
Title: Re: Plod calibrated speedo
Post by: Kevin Wood on 13 March 2009, 16:52:14
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Quote
.... to be accurate to within 10% either + or -.  .......

I thought it was +0% -10%  :-/   :-/
ie it could never read slower than actual road speed.

That is certainly the case at SVA/IVA. I had to calibrate my kit car to read high because if they run it at 70 on the rollers and it reads a gnat's under, it's failed.

The probem is, it means that even if manufacturers are making relatively accurate speedos they are already aiming at having them read high. ::)

IIRC at 70 MPH indicated, the acceptable true road speed range of 57 - 70 MPH was specified.

Kevin
Title: Re: Plod calibrated speedo
Post by: going crazy on 13 March 2009, 16:57:44
Would agree with the post above - tomtom says the speedo is out by around 2-3 mph at 7- mph
Title: Re: Plod calibrated speedo
Post by: PaulW on 13 March 2009, 17:29:19
In the Elite (non-calibrated), indicated 70mph is 65mph satnav
In the MV6 (calibrated), indicated 70mph is 70mph satnav
Title: Re: Plod calibrated speedo
Post by: TheBoy on 13 March 2009, 17:42:27
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In the Elite (non-calibrated), indicated 70mph is 65mph satnav
In the MV6 (calibrated), indicated 70mph is 70mph satnav
Wouldn't get too hung up on thinking the satnavs are accurate, though in your particular case, at the time you tested, seems reasonably accurate
Title: Re: Plod calibrated speedo
Post by: VXL V6 on 13 March 2009, 18:34:15
If you use the Tech II calibration check for the speedo it should read +3Mph above actual across the whole range IIRC.

Title: Re: Plod calibrated speedo
Post by: vauxmad on 13 March 2009, 19:16:38
even calibrated pieces of equipment have a tollerance that they can opeprate within, although calibrated equipments tollerance is very much smaller than an uncalibrated item!

same for everything including speedo's, nothing will be exactly 100% accurate there will be a small margin but on things like speedo's it will be smaller than read and then transfered as usable info to the driver.
Title: Re: Plod calibrated speedo
Post by: Martin_1962 on 13 March 2009, 19:25:39
Can you remove the overread with Tech2?
Title: Re: Plod calibrated speedo
Post by: tyreburner on 13 March 2009, 19:37:35
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I would say they would be right on the money - I got stopped once and question the accuracy and was shown a report which stated the speedo was tested for accuracy that very morning  :'(

Was always under the impression every day, but reading the next post once a week seems more realistic, all i know is plod dont like it when you ask to see the speedo caliberation paperwork, especially if they aint got any  8-)
That might be why they checked my spare, handbrake, seatbelts? and made sure the battery was secure and i had screen wash in the  bottle and it worked   :D ;D ;D
Title: Re: Plod calibrated speedo
Post by: tyreburner on 13 March 2009, 19:39:19
Quote
Quote
In the Elite (non-calibrated), indicated 70mph is 65mph satnav
In the MV6 (calibrated), indicated 70mph is 70mph satnav
Wouldn't get too hung up on thinking the satnavs are accurate, though in your particular case, at the time you tested, seems reasonably accurate
Must admit the sat nav tends to agree within 1mph of most of the caliberated coaches i drive  :y
Title: Re: Plod calibrated speedo
Post by: VXL V6 on 13 March 2009, 19:43:37
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Can you remove the overread with Tech2?

Speedo's should over-read by a set margin, far more preferable than under-reading from a legal point of view.

Title: Re: Plod calibrated speedo
Post by: Mr Skrunts on 13 March 2009, 20:29:32
I found it interesting in my Carlton Diplt.  Set the cruise on the motorway at 70.  Reset the fuel computer ro - - - both the fuel computer and the Tomtom in the car were showing 66mph (average speed on FC)  Rest it 4 or 5 times and was on faily level motorway.  So trusted 2 of the 3 to be correct.

Also handy to know exactly what the speedo reads at 70mph
Title: Re: Plod calibrated speedo
Post by: hotel21 on 13 March 2009, 20:39:21
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Quote
I would say they would be right on the money - I got stopped once and question the accuracy and was shown a report which stated the speedo was tested for accuracy that very morning  :'(

Was always under the impression every day, but reading the next post once a week seems more realistic, all i know is plod dont like it when you ask to see the speedo caliberation paperwork, especially if they aint got any  8-)
That might be why they checked my spare, handbrake, seatbelts? and made sure the battery was secure and i had screen wash in the  bottle and it worked   :D ;D ;D

Dunno about down south but, up here, all thats recorded is a notebook entry to say the daily checks were done and there is no requirement to show that entry to any offender.  

If a case subsequently goes to trial then a Certificate of Accuracy for the relevant device for the day is prepared and submitted by the Officers dealing.  The notebook entry is evidence to verify.  That entry (or its lack) would then be a legal argument at trial.....