(Very) Noisy GPS Long/Lat Accel Channels

Daniel
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Joined: Wed Mar 27, 2013 12:30 am
Location: Australia
Contact:

(Very) Noisy GPS Long/Lat Accel Channels

Postby Daniel » Wed Mar 27, 2013 10:51 am

Hi,

I recently bought the DL1 Mk3 (20Hz version) and am having trouble with the GPS channels.

I have installed the unit as per all instructions and the unit was bought new and is in good condition. I have checked the GPS antenna connector on the logger and it receives 3.3V.

When I turn the logger on I wait for the GPS Lock light to illuminate a solid green and then start logging after that (I have also tried waiting for 5 minutes with the logger on before starting to log). However the GPS Long Accel and GPS Lat Accel results are very poor (Speed seems fine). In particular when I export the data (at 10Hz) to Excel I get the following results:
• Satellite count is always zero
• GPS Long Accel and Lat Accel are very noisy to the point of unusable

Below is a graph of my GPS Lat Accel data taken from a slow test drive around the block.

Image

Can you please suggest how this can be corrected?

Thanks - Daniel

corey_dyck
Posts: 38
Joined: Mon Jun 30, 2008 2:45 pm
Location: Winnipeg, MB

Postby corey_dyck » Thu Mar 28, 2013 12:52 am

1.5 G spikes indicate something funny, unless your drive around the block is a lot more fun than mine! :P

For a simpler test: Take the logger off whatever it's mounted to and start logging. Then put it on its side. Then the other side, then the front, then the back. You should get nice flat lines at 1G other than the transitions. That may rule out mount vibrations or some other issue. If it looks like the above graph during this test, something is very wrong.

Daniel
Posts: 3
Joined: Wed Mar 27, 2013 12:30 am
Location: Australia
Contact:

Postby Daniel » Thu Mar 28, 2013 1:11 am

Hi corey_dyck,

Doesnt everyone drive around the block at 1.5G with massive oversteer moments?

I will try your suggestion tonight. I am not confident though because it is the GPS channel (not the accelerometers).

Looking at the data at the very start when the car is stationary you can see there isnt much happening - as expected. Also there does appear to be a signal within the noise, the faint blue line is the accelerometer lateral acceleration and you can see that in the corners the GPS Lat Accel does trend in a similar way.

Looking at it again it really looks like a bad connection. I will double check that again too.

KR
Daniel

Daniel
Posts: 3
Joined: Wed Mar 27, 2013 12:30 am
Location: Australia
Contact:

Postby Daniel » Thu Mar 28, 2013 1:37 am

Hi corey_dyck,

I tried your test. The test was done stationary and the GPS connection was checked. Below are the results:

Image

The accelerometers in red look great. The GPS in blue is all noise. Note that the scales are not the same - the GPS measurement is +/- 8G noise when stationary.

At this point it is either the antenna or a connection inside the logger. Can anyone recommend electrical tests to perform on the antenna at the connector?

KR
Daniel

Support

Support

Postby Support » Thu Mar 28, 2013 10:22 am

Hello,

The GPS accelerations are calculated. When you are stationary the GPS thinks you are moving around albeit not very much this movement would still require high g-forces.

You need to add heavy filtering to get any thing useful from GPS accelerations.

Regards,
Support


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