JusticeForPorygonWhy the duck do cars still have analog speedometers? Surely digital ones would be more accurate and much easier to read without looking away from the road for too long.
NakedmoleBecause analog sensors are more accurate than digital ones and that is because they are analog. While an analog system has unlimited resolution, digital systems require a quantization of the sensor data and that is a clear disadvantage when it comes to precision.
Atemu“Didn’t understand the sampling theorem” for $2 please.
As long as the frequency of the measured signal is <1/2 the sample rate, you can reconstruct the original signal perfectly.
If you plugged this jaggy-looking graph into a digital to analog converter with perfect analog circuitry, you’d get exactly the sine shown.
qjkxbmwvzI think parent is referring to quantization in the amplitude/y-axis (bitdepth), whereas you are referring to quantization in time/x-axis (sampling rate).
Quantisation is a potential factor but the graph does not show its effects and their comment describes the supposed effects sampling, not quantisation.
Also, when we come to discussing SNR, you’ll have to consider the SNR of analog systems too.
The graph posted absolutely exhibits both quantization and discrete sampling. The blue trace on the Y-axis shows steps of 1 — that’s quantization.
I should have been more clear: The negative effects of quantisation. Obviously sampling into discrete values is shown but not the negative consequences that can have.
A DAC interpreting the blue trace will output something extremely close to the red one. There might be a slight bit of error in it due to the quantisation before but the graph does not show that and it probably couldn’t since it’d be so tiny. A good way to show quantisation noise would be a histogram with a signal in the middle and some quantisation noise around it.
The DAC would not output the jaggy line. It couldn’t, that’s not a valid analog signal. Painting the steps between the points can be done if your audience knows what that means but can be extremely misleading if it doesn’t. Those lines between the points with 90 degree angles don’t exist in the real world, they’re just interpolated between the points in the visualisation.
A much better way to represent digital samples in such a chart is the way it’s done in the wikipedia article on the topic: en.wikipedia.org/…/Sampling_(signal_processing). They’re just discrete points. If you did the same interpolation between the points as a DAC would do (which is not nearest-neighbour interpolation), you’d get the analog trace shown.
Sorry if I caused confusion by quickly choosing a random graph or maybe by failing to explain what I mean properly. It has been a long time since I learned about A/D and I might probably have mixed up a few details. However - my point still stands - if you look at the graph you will see that the analog speedometer always knows and thus displays the exact speed of the car in any moment (plus a small inevitable speedometer system delay). The digital speedometer on the other hand most of the time shows only the quantized value of the last taken sample - except in the exact moments when the samples are taken.
Interesting. Does quantization not always refer to quantization of the amplitude value of a sample while the sampling rate is always referred to as the … sampling rate? I get what you mean by quantization of time but I have never heard anyone calling the sampling rate that before, so now I´m asking myself if it even is a real quantization because there is no approximation going on and the frequency is an exactly known value at all times.
Yes I think you used the terms correctly — it should be referring to the amplitude. “Discrete sampling” or just sampling rate is the preferred way to refer to time, you’re right.
I was trying to use consistent language in response to the reply claiming you were misunderstanding the sampling theorem. I think that poster was confusing discrete/quantized steps in time with discrete/quantized steps in amplitude.
Their comment about SNR is certainly true though.
There are a whole bunch of problems with this:
- most of the sensors are digital
- the guages are getting their signals from the ECU computer, which is a digital signal
- the guages in your car are not $10000 scientific equipment, they’re not that precise.
- the design of these analog guages means that most precision would be lost just due to human vision.
There are good arguments for analog guages in cars, but precision isn’t one.
Interesting! Thank you!