Is GPS out of M800 serial / CAN untouched or filtered?

Information about using GPS units with motec devices

Is GPS out of M800 serial / CAN untouched or filtered?

Postby Chris Wilson on Wed Dec 07, 2011 6:34 am

Is the GPS from the 5Hz Motec GPS receiver output totally unfiltered via RS232 into an M800? Why do I ask? If I log it internally via the M800 itself the results in i2 are fine, if I log it via CAN to A N Other standalone logger there are spikes in the rendered map until the vehicle / GPS receiver is moving. It's unfair to ask you to help with A N Other logger, but will you just tell me if the output of the 5 Hz receiver is manipulated or filtered in any way before being either logged internally in the ECU or spat down the CAN bus via a custom data set?

Thanks.
Chris Wilson
 
Posts: 231
Joined: Mon Jul 14, 2008 7:51 am

Re: Is GPS out of M800 serial / CAN untouched or filtered?

Postby Holmz on Wed Dec 07, 2011 7:00 pm

Chris Wilson wrote:Is the GPS from the 5Hz Motec GPS receiver output totally unfiltered via RS232 into an M800? Why do I ask? If I log it internally via the M800 itself the results in i2 are fine, if I log it via CAN to A N Other standalone logger there are spikes in the rendered map until the vehicle / GPS receiver is moving. It's unfair to ask you to help with A N Other logger, but will you just tell me if the output of the 5 Hz receiver is manipulated or filtered in any way before being either logged internally in the ECU or spat down the CAN bus via a custom data set?

Thanks.


I put a 10-Hz into a STC (serial to CAN), and that works.
(I know 10-Hz is not 5-Hz)

You could use a "Y" connector and put the RS232 into the M800, and put the other side of the "Y" into a STC and see if the data is the same.

I think that there is also some 'math(s)' in the i2 that makes 'unlocked' reading 'out of range' and not plot, so that might be what is happening.
I would look at the logged "number of satellites" in i2 and see if it is dropping out, which would make it 'look' filtered in i2.
User avatar
Holmz
 
Posts: 521
Joined: Fri Dec 19, 2008 5:19 pm
Location: Australia and the USoA

Re: Is GPS out of M800 serial / CAN untouched or filtered?

Postby OmarK on Thu Dec 08, 2011 3:52 pm

You should note the GPS lat, long and time are split into Low Word and High Word but when logged i2 recombines them into full lat, long and time channels. I would split the RS232 signal from the GPS to the ECU and the RS232 input of your data logger. What is your other logger by the way?
OmarK
 
Posts: 214
Joined: Mon Nov 10, 2008 3:39 pm
Location: UK

Re: Is GPS out of M800 serial / CAN untouched or filtered?

Postby Chris Wilson on Fri Dec 09, 2011 1:03 am

OmarK wrote:You should note the GPS lat, long and time are split into Low Word and High Word but when logged i2 recombines them into full lat, long and time channels. I would split the RS232 signal from the GPS to the ECU and the RS232 input of your data logger. What is your other logger by the way?


Hi Omar, thanks for the reply. The logger is a GEMS DA-99L2 one gigabyte device from here in the UK. The GEMS logger does the maths to add the channels back up internally, in the same way i2 does it, externally combining them. I have allso tried turning the logger maths off and performing the maths in the viewing software, with no change. I am comparing maps from the same session, logged at the same time, one via RS232 direct into my M800, and viewed in i2, and the other logged by the GEMS logger via CAN output from the M800. The attachment below shows how the GEMS software displays the session, note the seemingly random "spikes". These mainly disappear if the log is truncated, losing the beginning and end of the session where the vehicle is stationary. I suspect the i2 display is uncorrupted due to some standard internal filtering, and the raw data as seen by both the M800 internal 1 meg logging, and the CAN bus derived data that the GEMS logger is reading, are identical? The devil being in the filtering algorithms used? I believe the GEMS logger does have an RS232 input, I could try using that, but do you feel this is a filtering issue, rather than how the data is input?

Thanks again.

http://www.gatesgarth.com/track_map.jpg

http://www.gatesgarth.com/DA99L2.pdf
Attachments
track_map.jpg
track_map.jpg (740.2 KiB) Viewed 11700 times
Chris Wilson
 
Posts: 231
Joined: Mon Jul 14, 2008 7:51 am

Re: Is GPS out of M800 serial / CAN untouched or filtered?

Postby Holmz on Fri Dec 09, 2011 7:24 am

Chris - can you correlate the spikes with the number of satellites (or when that number is zero) ?
User avatar
Holmz
 
Posts: 521
Joined: Fri Dec 19, 2008 5:19 pm
Location: Australia and the USoA


Return to GPS Information

Who is online

Users browsing this forum: No registered users and 0 guests