Date: Mon, 25 Oct 2004 20:07:24 GMT From: "SAABurger" <furnyburgernospamorld.com> Subject: Re: 9000 green arrow?
To add a little more meat to Keith G's response .... From 9000 CS Owner's Manual 1992, "Indicator and Warning Lights", p5: "Fuel Warning Light: This light will show when less than approximately 10 litres (2 imp. gal) of fuel remains in the tank." From 9000 CS Owner's Manual 1992, "Trip Computer", p7: "Range of the car, based on the amount of fuel left in the tank and the average fuel consumption. When the range falls below about 30 miles (50km) and one of the other functions has been selected, the arrow on the display will start to flash." [From observation, I believe this to be a incorrect and incomplete description. In my 1992 9000 CS the threshold appears to be 50 miles not 30, and the "average" fuel consumption appears to be a very recent average, not the average since last reset as displayed to the driver] I have always believed the "pump" warning and the "arrow-dot" warning both to be based on the signal from the fuel lever sender. As far as I'm aware that's the only thing that 'knows' how much fuel there is in the tank. In the absence of a second sensor mechanism (which I believe to be the case), the differences between the two indications lie not in the source of the signal but in the way it is interpreted, as follows: "Pump" warning - Compared with a voltage threshold corresponding to the design warning level of 10 litres. Possibly engineered as a separate contact on the sender. "Arrow-dot" warning - Digitised and subjected to a digital calculation of miles/kilometres left in the tank, incorporating recent MPG (or l/100km). ***** STOP HERE UNLESS YOU ARE KEEN, PEDANTIC AND/OR SLIGHTLY NUTS ***** Now <big breath> for Accuracy and Precision, into which I should not be drawn (been there, done it and regretted it and whoops here I go again). This is the subject of essay answers in university Computing/Engineering exams for which "Accuracy" and "Precision" are well defined terms. Both warnings have identical display precision; they are both 1 bit, binary messages. In the absence of full engineering data, we can only guess at the relative accuracy of the two warnings. Both devices certainly inherit all the inaccuracy of the sender so that is not a discriminating factor. Any difference in accuracy will depend on the relative accuracy of : For the "Pump" warning - the device(s) which afford the threshold voltage and perform the comparison of this against sender signal level. For the "Arrow-dot" warning - the device(s) which measure, digitise and integrate the fuel flow and the device(s) which measure distance travelled. We don't know but the "Arrow-dot" warning may actually have a poorer accuracy than the "Pump" warning. Having said that, it's not strictly valid to compare the accuracy of two things which are displaying different data items, even if they are closely related and based in part on the same source signal. Given that these warnings both mean (and are generally interpreted as) nothing more than "get to a petrol station pretty soon" it is probably fair to say that both are acceptably accurate. For my money, and putting accuracy and precision issues aside, the flashing "arrow-dot" is the *better* warning as it takes account the recent rate of fuel consumption. To round off the discussion, it may be worth noting that no signal, however precise or accurate, is useful if its meaning is not known. Congratulations if you read all the way down to here. Answers on a postcard please. Adrian Hampshire England "maxandanna" <sorry.you.cnospamave.it> wrote in message news:MPG.1be5a4b7b8c3702698969enospam-text.blueyonder.co.uk... > In article <n9SdnR-_B_FBDebcRVn-sQnospamopenwest.com>, noonenospamay.com > says... > > Yes, The EDU will show a dot with an arrow whenever the fuel left is at > > a preset value (45 miles?). This appears regardless of which mode you > > are displaying (volts, consumption, temp, etc...) This is in addition to > > the little orange petrol pump icon. That icon is tied only to the fuel > > lever sender and is not nearly as accurate or precise as the EDU which > > takes the fuel level and consumption information to display that > > flashing arrow. > > > > KeithG > [snip] > > Keith, thank-you for a clear explanation. > > Max > > -- > www.maxandanna.pwp.blueyonder.co.uk
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