LTI 20-20 UltraLyte 100 Calibration checks
Discussion
Devil2575 said:
Pete317 said:
Yes, you measure distance by measuring ohow long
No, you measure time and convert it to speed/distance using a constant. What the device needs to be able to do is emit and dectect a beam of light and measure time. Pete317 said:
Devil2575 said:
Pete317 said:
Yes, you measure distance by measuring ohow long
No, you measure time and convert it to speed/distance using a constant. What the device needs to be able to do is emit and dectect a beam of light and measure time. Devil2575 said:
Pete317 said:
Devil2575 said:
Pete317 said:
Yes, you measure distance by measuring ohow long
No, you measure time and convert it to speed/distance using a constant. What the device needs to be able to do is emit and dectect a beam of light and measure time. The point is that it's wrong to suggest that one can obtain a speed without invoking the exact same method as used for measuring distance - which also implicitly gives you a measure of distance, whether you use it or not.
Pete317 said:
When you take the measurement, you're getting a measure of the time and of the distance at the same time, and you can't get a measure of the one without also getting a measure of the other - what you call the measurement depends on what you do with it.
The point is that it's wrong to suggest that one can obtain a speed without invoking the exact same method as used for measuring distance - which also implicitly gives you a measure of distance, whether you use it or not.
Speed = distance/time so the three are linked. What it measures is time, it can then calculate speed and or distance. To argue which it does first it fairly meaningless. The point is that it's wrong to suggest that one can obtain a speed without invoking the exact same method as used for measuring distance - which also implicitly gives you a measure of distance, whether you use it or not.
Devil2575 said:
Pete317 said:
When you take the measurement, you're getting a measure of the time and of the distance at the same time, and you can't get a measure of the one without also getting a measure of the other - what you call the measurement depends on what you do with it.
The point is that it's wrong to suggest that one can obtain a speed without invoking the exact same method as used for measuring distance - which also implicitly gives you a measure of distance, whether you use it or not.
Speed = distance/time so the three are linked. What it measures is time, it can then calculate speed and or distance. To argue which it does first it fairly meaningless. The point is that it's wrong to suggest that one can obtain a speed without invoking the exact same method as used for measuring distance - which also implicitly gives you a measure of distance, whether you use it or not.
Pete317 said:
Devil2575 said:
Pete317 said:
When you take the measurement, you're getting a measure of the time and of the distance at the same time, and you can't get a measure of the one without also getting a measure of the other - what you call the measurement depends on what you do with it.
The point is that it's wrong to suggest that one can obtain a speed without invoking the exact same method as used for measuring distance - which also implicitly gives you a measure of distance, whether you use it or not.
Speed = distance/time so the three are linked. What it measures is time, it can then calculate speed and or distance. To argue which it does first it fairly meaningless. The point is that it's wrong to suggest that one can obtain a speed without invoking the exact same method as used for measuring distance - which also implicitly gives you a measure of distance, whether you use it or not.
A tape measure gives a measure of distance. A clock gives a measure of time. This device measures a time difference and converts it into a distance. They key is that it requires the ability to do a calculation to determine speed and distance. Someone physically has to program in the speed of light to enable it to do this.
In my line of work we do a lot of measurement by different techniques. Understanding what the measuring device is actually measuring and how it is giving you the reading is kind of key to understanding potential sources of error.
A speed gun measures time and calculates speed and distance. It does not measure distance.
Devil2575 said:
Distance in what sense? It doesn't have to calculate absolute distance, but it does essentially determine distance travelled by the car between pulses.
A tape measure gives a measure of distance. A clock gives a measure of time. This device measures a time difference and converts it into a distance. They key is that it requires the ability to do a calculation to determine speed and distance. Someone physically has to program in the speed of light to enable it to do this.
In my line of work we do a lot of measurement by different techniques. Understanding what the measuring device is actually measuring and how it is giving you the reading is kind of key to understanding potential sources of error.
A speed gun measures time and calculates speed and distance. It does not measure distance.
A tape measure gives a measure of distance by counting the number of evenly-spaced ticks between the start and end. A clock gives a measure of time by counting the number of swings that a pendulum has made. This device gives a measure of distance by counting the number of clock cycles for a laser pulse to be returned.A tape measure gives a measure of distance. A clock gives a measure of time. This device measures a time difference and converts it into a distance. They key is that it requires the ability to do a calculation to determine speed and distance. Someone physically has to program in the speed of light to enable it to do this.
In my line of work we do a lot of measurement by different techniques. Understanding what the measuring device is actually measuring and how it is giving you the reading is kind of key to understanding potential sources of error.
A speed gun measures time and calculates speed and distance. It does not measure distance.
Devil2575 said:
Pete317 said:
Devil2575 said:
Pete317 said:
When you take the measurement, you're getting a measure of the time and of the distance at the same time, and you can't get a measure of the one without also getting a measure of the other - what you call the measurement depends on what you do with it.
The point is that it's wrong to suggest that one can obtain a speed without invoking the exact same method as used for measuring distance - which also implicitly gives you a measure of distance, whether you use it or not.
Speed = distance/time so the three are linked. What it measures is time, it can then calculate speed and or distance. To argue which it does first it fairly meaningless. The point is that it's wrong to suggest that one can obtain a speed without invoking the exact same method as used for measuring distance - which also implicitly gives you a measure of distance, whether you use it or not.
A tape measure gives a measure of distance. A clock gives a measure of time. This device measures a time difference and converts it into a distance. They key is that it requires the ability to do a calculation to determine speed and distance. Someone physically has to program in the speed of light to enable it to do this.
In my line of work we do a lot of measurement by different techniques. Understanding what the measuring device is actually measuring and how it is giving you the reading is kind of key to understanding potential sources of error.
A speed gun measures time and calculates speed and distance. It does not measure distance.
If you're measuring the time then you're also implicitly measuring distance - and vice versa.
And in any case, do you say you can't actually measure distance in situations where it's impossible to use a tape measure? Or would that be overly pedantic?
ETA: Anyway, it doesn't even measure time, but rather it counts the number of clock pulses which occur between the time that the pulse is sent and the time its echo is received.
Edited by Pete317 on Thursday 26th November 20:37
Devil2575 said:
Speed = distance/time so the three are linked. What it measures is time, it can then calculate speed and or distance. To argue which it does first it fairly meaningless.
You have confused yourself. The machine does two calculations. Firstly it uses a known speed (of light) and a measurement of time (of reflection) to calculate a distance to the vehicle. This is repeated one or more times.
Secondly it uses the change of distance between two or more of the above readings, at a known change of time (calculated by its internal clock) to calculate the vehicle's speed.
V8LM said:
Devil2575 said:
Distance in what sense? It doesn't have to calculate absolute distance, but it does essentially determine distance travelled by the car between pulses.
A tape measure gives a measure of distance. A clock gives a measure of time. This device measures a time difference and converts it into a distance. They key is that it requires the ability to do a calculation to determine speed and distance. Someone physically has to program in the speed of light to enable it to do this.
In my line of work we do a lot of measurement by different techniques. Understanding what the measuring device is actually measuring and how it is giving you the reading is kind of key to understanding potential sources of error.
A speed gun measures time and calculates speed and distance. It does not measure distance.
A tape measure gives a measure of distance by counting the number of evenly-spaced ticks between the start and end. A clock gives a measure of time by counting the number of swings that a pendulum has made. This device gives a measure of distance by counting the number of clock cycles for a laser pulse to be returned.A tape measure gives a measure of distance. A clock gives a measure of time. This device measures a time difference and converts it into a distance. They key is that it requires the ability to do a calculation to determine speed and distance. Someone physically has to program in the speed of light to enable it to do this.
In my line of work we do a lot of measurement by different techniques. Understanding what the measuring device is actually measuring and how it is giving you the reading is kind of key to understanding potential sources of error.
A speed gun measures time and calculates speed and distance. It does not measure distance.
schmunk said:
Devil2575 said:
Speed = distance/time so the three are linked. What it measures is time, it can then calculate speed and or distance. To argue which it does first it fairly meaningless.
You have confused yourself. The machine does two calculations. Firstly it uses a known speed (of light) and a measurement of time (of reflection) to calculate a distance to the vehicle. This is repeated one or more times.
Secondly it uses the change of distance between two or more of the above readings, at a known change of time (calculated by its internal clock) to calculate the vehicle's speed.
I'll take your word for the next bit. I'm assuming you're speaking for a position of knowledge of how it actually works. It could just as easily measure the change of time for reflection between measurements and convert that into a speed. It doesn't need to do continuous distance measurements.
cptsideways said:
I wish I had read this bit first Hahahahahhahahhahahhahah
Let me give you a clue, they measure distances over time. Which is partly why they are inaccurate as the distance part is the difficult bit with moving targets.
Ok, I'll bite.Let me give you a clue, they measure distances over time. Which is partly why they are inaccurate as the distance part is the difficult bit with moving targets.
If a car is 100 m away and travelling towards you at 100 km/hr or 27.8 m/s
The beam will take 6.7 E-11 or 0.000000000067 seconds to get to the car and back.
In that time the car will have travelled 0.00000000185 m or to put that another way, 0.00000185 mm.
To put it another way, the light travels so fast that the car might was well be stationary.
Rovinghawk said:
Monty Python said:
You're quite correct - anything that measures distance by light can be affected by all manner of issues caused by reflection, refraction, absorption, scattering and a bunch of other processes.
Temperature, air pressure & weather also have an effect- light rain is a worse problem than heavy rain for some strange reason.Rain could have an effect because light is refracted when it passes through a medium like water.
Devil2575 said:
schmunk said:
Devil2575 said:
Speed = distance/time so the three are linked. What it measures is time, it can then calculate speed and or distance. To argue which it does first it fairly meaningless.
You have confused yourself. The machine does two calculations. Firstly it uses a known speed (of light) and a measurement of time (of reflection) to calculate a distance to the vehicle. This is repeated one or more times.
Secondly it uses the change of distance between two or more of the above readings, at a known change of time (calculated by its internal clock) to calculate the vehicle's speed.
I'll take your word for the next bit. I'm assuming you're speaking for a position of knowledge of how it actually works. It could just as easily measure the change of time for reflection between measurements and convert that into a speed. It doesn't need to do continuous distance measurements.
Assume I'm a simpleton.
schmunk said:
Please explain how it calculates the speed of the vehicle before it's firstly calculated the distance to the vehicle two or more times. [N.B. where the speed of the pulse is known, calculating the journey time == calculating the distance]
Assume I'm a simpleton.
Example.Assume I'm a simpleton.
Pulse 1 takes X seconds
Pulse 2 takes X -10 seconds
Pulses are 1 second apart.
Speed of car is 10/2 x Speed of light x time between pulses.
I've used big numbers for the purpose of demonstration.
I'm not saying this is how it works, but it could.
First ping is returned in 10 ticks.
Second ping is returned in 9 ticks.
10 ticks between first and second ping.
(10 - 9) / 10 = 0.1
0.1 * c / 2 = 1.5x10^7 m/s
So, don't need time. However, does measure distance in terms of "light-ticks" - 10 for the first and nine for the second.
Second ping is returned in 9 ticks.
10 ticks between first and second ping.
(10 - 9) / 10 = 0.1
0.1 * c / 2 = 1.5x10^7 m/s
So, don't need time. However, does measure distance in terms of "light-ticks" - 10 for the first and nine for the second.
Edited by V8LM on Friday 27th November 06:54
But, all that is referenced against the the constant of the speed of light.
That reference constant is the distance light travels between pulses. To argue that it does not measure distance at pulses A, B, C, D and so on is silly.
You can't measure a delta unless you have two readings - those readings are a measure of distance.
That reference constant is the distance light travels between pulses. To argue that it does not measure distance at pulses A, B, C, D and so on is silly.
You can't measure a delta unless you have two readings - those readings are a measure of distance.
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