# Odometer function

Phil Gooch

Posted on 02.06.2016 09:35

We are conducting some tests on rail vehicles where we must travel at over 77km/h for a distance of 3000m

Our setup is:

• Dewe43.
• GPS receiver used for position and velocity.
• Tri-axial accelerometer.

What is the best way to create a display, such as a digital meter, that functions as an odometer only when a target speed has been reached? So, during acceleration the display reads 0m but as soon as the speed goes above 77km/h it begins counting. When the speed drops below 77km/h it stops counting.

DEWESoft Support
Technical support
Posted on 02.06.2016 13:33

Hi,

I've created two example setups that should help you with your application. The first setup is made in simulation mode, where the user can control the velocity slider. If the slider is placed over 77 km/h, the distance will start being calculated and added up. It's set so that it multiplies each velocity reading with the time that this velocity is preset, which in this case equals to 1 divided by the sample rate. The distance is then displayed on a digital and analog meter for a better feeling of where you are compared to your goal. If the velocity drops below the threshold, the distance will no longer be added. The calculation then resumes when the velocity is back over 77 km/h.

As for your real measurement, I'm not sure if the velocity that you'll be using for your calculations will be coming from the GPS receiver, or will be calculated from the acceleration sensors. If you'll be using the GPS, you'll have to take in account it's refresh rate. In the second, real measurement setup, I've added another math field, in which you can enter the frequency of the GPS. The other calculations and displays are the same as before.

Attached files:
Phil Gooch

Posted on 03.06.2016 01:05

Thanks for your assistance. We will be using GPS for our speed and I'm not sure how to determine the refresh rate - Is this driven by the hardware of a Dewesoft setting?

If it is hardware, is there a way to use DeweSoft to determine the refresh rate?

DEWESoft Support
Technical support
Posted on 03.06.2016 07:49

Hi,

yes, it's hardware dependent. You can use DEWESoft to determine the frequency of the data that's coming in from the GPS. In your case, you can simply display the velocity signal on a recorder screen, freeze the measurement, zoom in enough and place the zoom cursors on two neighbor data points. In the bottom left corner, you will see the time between them, and the inverse of the time is of course the frequency, which will also be displayed. The data will usually come in at around 1 Hz, 10 Hz or even 100 Hz, so you can clearly distinguish your GPS's frequency.

I've attached a picture of my GPS test. Even tough the data is at zero, you can still determine it's sample rate, which in my case is 1 Hz.

Attached files:
Phil Gooch

Posted on 03.06.2016 08:09

Thanks, that works well.

Daniel Turner

Posted on 07.06.2016 09:24

Hi,

I have a similar odometer query, so thought I would tag onto this post.

We are completing a similar vehicle test using a 10Hz Locosys GPS. We have to complete a certain distances at different speeds, in a specific order. Once we have completed the first distance at a certain speed, we then have to complete the next distance at a different speed. The test procedure is as follows:

1) 3km at a speed over 50km/h, then;

2) 22 @ 50km/h, finally;

3) 75km@25km/h

Is it possible to set this up in DEWESoft using three separate odometers for each of the test parts (IF functions)? With the second odometer (22km @50m/h) only starting to record once the first part (3km over 50km/h) has been completed? Following 22km@50km/h, odometer three should then start recording for 75km@25km/h?