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ScanTool.net Forum  |  Hardware  |  OBDLink SX  |  Topic: OBDlink SX: Question about bandwidths and sampling rate « previous next »
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Author Topic: OBDlink SX: Question about bandwidths and sampling rate  (Read 1814 times)
vvo2000
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« on: November 17, 2011, 01:22:06 PM »

Hi,

I have recently bought OBDlink SX & OBDwiz to run diagnostics on a 1999 Toyota 4runner  4WD 3.4L  gas  5VZ-EF.  I installed recent OBDWiz software from the web-site and usb drivers from CD on a windows XP laptop; everything seems to work fine.

After connecting to the car  via "auto-detect connection", program shows connection "ISO 141-2 @ 10.4KBaud",  lower right corner of the OBDWiz window shows between 6 and 10 PIDs/sec.


I would like to look at O2 sensor(s) voltage at real-time, but it seems that data sampling rate is not fast enough.
Assuming I can use  the whole bandwidth for reading only one parameter,
 I have selected only one parameter (O2 sensor) on a chart , but it still samples O2 voltage once in 0.6-1 seconds.
Enabling/disabling 'Fast Polling' does not change the situation. O2 sensor priority is set to 1 (highest?).


Could you please tell me if there a way to sample one sensor several times per second?
I guess if transfer rate is 6-10 points per second, it should be good enough to sample an O2 sensor sine-wave with  ~1 sec repetition rate.

Is it typical to have 6-10 PID/second sampling rate in my setup or is it an indication that something is not quite right?
On screen-shots from OBDWiz help files, numbers are something like 60PID/sec.

Thank you in advance,

Evgeny

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Jason Smith
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« Reply #1 on: November 17, 2011, 02:29:14 PM »

Hi Evgeny,

Unfortunately, ISO 9141-2 is a very slow protocol. 6 to 10 PIDs/s is pretty good, on my vehicle I get 3 to 5 PIDs/s.

If you're polling only one the O2 sensors, I don't know why you wouldn't see the same PID rate. Can you post a "Raw Data" log (Diagnostics->Raw Data)?

If your vehicle supports Mode $05 (Monitors->Oxygen Sensors), I would use this test to verify O2 sensor operation.

Regards,
Jason
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vvo2000
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« Reply #2 on: November 17, 2011, 02:52:17 PM »

Hi Jason,

thank you very much for the quick answer and for the clarification!

Monitors -> Oxygen Sensors showed that both sensors are OK.

I will post raw data later when I have another chance to play around with diagnostics.
There is definitely a learning curve involved, too Smiley

Best,
Evgeny

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Jason Smith
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« Reply #3 on: November 17, 2011, 03:54:08 PM »

Thank you, and I'm glad your O2 sensors passed  Wink.

Jason
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mjo151
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« Reply #4 on: November 17, 2011, 06:28:54 PM »

Hi Evgeny,

As Jason mentioned, the fundamental problem is that the protocol that your vehicle supports (ISO 9141) is very slow. However, you can get the fastest response for one sensor by doing the following:

1. Make sure you are running the latest version (2.12 or later).
2. On the Setup->PID Monitor page, make sure Fast Polling is enabled and the dwell time is set to 0 msec.
3. On the Setup->Fuel Setup page, select "None" as the Fuel Calculation Method (this will turn off all fuel calculations).
4. On the Setup->Connection page, click the "Decrease Port Latency" button, if it is enabled.
5. When you go to plot the sensor, select only the sensor(s) that you care about seeing.

Regards,
Matt
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vvo2000
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« Reply #5 on: November 22, 2011, 03:01:54 PM »

Update:

Did everything as you guys suggested, it seems to work - in csv files data points are sampled 3-8 times per second depending on a number of PIDs chosen. That correlates with 6-10 PID/sec rate displayed by the OBDwiz.

My O2 sensor is likely a wide-band A/F sensor, so I probably should not expect "textbook oscillations" in O2 voltage readings. Sensor's behaviour is a bit sluggish though, so I am going to replace it anyway Smiley

Thanks a lot!
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Cfan
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« Reply #6 on: November 16, 2012, 04:24:22 PM »

Hi Evgeny,

Unfortunately, ISO 9141-2 is a very slow protocol. 6 to 10 PIDs/s is pretty good, on my vehicle I get 3 to 5 PIDs/s.

If you're polling only one the O2 sensors, I don't know why you wouldn't see the same PID rate. Can you post a "Raw Data" log (Diagnostics->Raw Data)?

If your vehicle supports Mode $05 (Monitors->Oxygen Sensors), I would use this test to verify O2 sensor operation.

Regards,
Jason

How many samples/second can one expect with Ford CAN? 2003-2010 Ford Diesel to be specific.   Anyone out there tried it on that vehicle?  I have a similar system to the OBDLink-SX and it is only recording 4-5 pids about 1sample/sec.  Best I can get is 2 samples/sec with one PID.   "Fast mode" is on.  I am considering getting the OBDLink-SX to try.  Are the other softwares any better?   All I really need it for is data logging, so I was hoping the OBDWiz would be enough.  I have heard it really only depends on the vehicle- but I'm not sure if that is entirely true since I know of very expensive equipment that will record well over 10 samples/sec on several pids.
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