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[zirk]

On the Ex Police ones, how was the Speedo Calibrated at the Garage?

Tech 2, via ECU or does it have its own Comms Port hidden away somewhere, ie could we on OOF re Calibrated it? (forgetting the Rolling Road bit which I assume is what they used as a Reference).

[Marks DTM Calib]

As with most calibrations, its a case of checking its in calibration rather than making any adjustments

[Kevin Wood]

Yep, the larger VOSA test stations, for example, have rolling roads for this purpose. Police workshops may have had their own, or taken them to VOSA for testing. Calibration just implies that any error is controlled within agreed tolerances when tested against traceable standards. There won't necessarily be any requirement to adjust it to remain within those tolerances. Certainly the Tech2 has no such capability that I've discovered.

[05omegav6]

They're calibrated on the bench by IRS according to the tyre size and gear/diff ratios so fitting auto clocks in a manual car will result in the speedo being out unless the diff went with it

This is also why my 18"s run 245/40 tyres as the rolling radius is identical to the original 225/55/16s

[Kevin Wood]

Gearbox and diff ratios make no difference to the speedo reading in an Omega since the speed is sampled at the hub by the ABS sensors.

Wheel size, however - yes, the instrument panel will be configured to suit the spec. of the car it's destined for, just like a standard dash.

The only real difference is that a "calibrated" dash will be targeting a different tolerance to an OEM dash.

Where an OEM dash is aiming at never under reading (so in reality, perhaps aiming at a 5-10% over-read to ensure this in all conditions), a police dash would presumably aim to read true speed for a tyre that's somewhere in the middle of the range of "wheel rev per mile" figures that it's likely to encounter with the spec. of tyre to be fitted.

Since the rest of the system is essentially just counting ABS sensor pulses per second and commanding a stepper motor to point the speedo needle at the right number on the dial, there isn't really any opportunity for a significant error to occur other than change in wheel RPM between new and worn tyres and between brands. Hence, I doubt there's anything special about the dash, nor any reason to adjust it once it's been initially set up.

[zirk]

Thanks, I assumed something was different with them as one of the reasons for asking is when I tried a Plod Dash in a normal Mig, the Speedo didn't work.

[05omegav6]

That be a duff unit

I only mentioned the gear ratios as my first Omega was ex plod and the cluster was labled with engine, gearbox and tyre size info... possibly a onelabelfitsall situation at IRS easier to put all the same info on every cluster that they calibrate, instead of remembering the variations between manufacturers The history for my '03 plod included the original calibration certificate, which again detailed all the information I referenced earlier

As far as I have seen, they still calibrate the current crop of plod vehicles

[05omegav6]

Just to add, the speedo face replaces the original speedo face, but as this is a sticker, it is impossible to dismantle the speedo unit without damaging the face, as the sticker covers the screw heads

[zirk]

That be a duff unit

No, its was being swapped with know good units, or was it the other way around Normal Dash into a Plod, cant remember now, some time back, either way it didn't work. 

[05omegav6]

Could have been pre/post facelift then have fitted non plod fl v6 into plod fl v6 with no issues

[Kevin Wood]

That be a duff unit

I only mentioned the gear ratios as my first Omega was ex plod and the cluster was labled with engine, gearbox and tyre size info... possibly a onelabelfitsall situation at IRS easier to put all the same info on every cluster that they calibrate, instead of remembering the variations between manufacturers The history for my '03 plod included the original calibration certificate, which again detailed all the information I referenced earlier

As far as I have seen, they still calibrate the current crop of plod vehicles

Yep. Some vehicles it will make a difference, some it won't, so might as well standardise and be on the safe side, I guess.

[zirk]

They were both from the same year Al, normal clocks from a W reg .3.0 MV6 into a X reg 3.0 Plod both FL, I remember now didn't like the xmas tree lights efect on the Plod clocks. Anyway as said probably me doing something wrong at the time.

[05omegav6]

Swapping the cluster with the ignition or lights on might have done it I guess

[Dave DND]

Just for info,

The speedo readings can indeed be recalibrated electronically by altering data in the processor on the back of the clocks - this allows for variation in wheel / tyre sizes etc - some of the more "advanced" companies offering mileage alteration are able to re-map these clocks should you want to go crazy on wheel sizes etc, but it relies on the clocks being plugged into an external programmer - (NOT on the car or via Tech2 etc.) We messed about with it for a while for the kit car market, but wasn`t really a viable enterprise for us, so we dropped it.

Not sure Plod was ever that advanced though, and as suggested, I would reckon that the calibration certificate was to guarantee that the indicated speeds were indeed within their tolerances should they ever be called into question.

Hope this helps.

[Marks DTM Calib]

All IRS do is feed a calibrated speed pulse signal in and check the readings (A neighbour works there as they are only just down the road).

This is pretty much what happens to all measuring kit these days sadly.