If some of you are keeping up with the ever-increasing features for PicoScope 7 Early Access, you may have seen a new filter called ‘Index of’.
All sounds rather impressive, but how can this help in the real world? One of the big questions we get asked about is how we can diagnose NOx sensors. Realistically, there is little output for these controllers as they typically only have 4 wires – power, ground, CAN H and CAN L. So, providing you have a good power supply, good ground and messaging happening, what else can we do?
There is an extensive post about J1939 decoding in the Off-Highway forum, including one that looks at decoding the NOx sensors – https://www.picoauto.com/support/viewto … 15#p100615.
NOx sensors are pretty standardised across Off-highway machinery and normally retain the same source address for up and downstream sensors. The introduction of the J1939 decoder really helped with splitting up the header part of the message and so separating out the priority, PGN and Source address. We can then highlight just the NOx sensors using a filter. Using other information in the above post, we can filter out just the upstream and downstream NOx sensors by using the PGN for both. For ease, I’ve kept the decode tables in HEX values.
To begin with, we can create additional decode tables and then, using the filter function, we can only display the individual PGNs for up and downstream NOx sensors. For upstream, the PGN of interest is 0F00E and for downstream, 0F00F.
What is quite nice is that when applying filters to the decode table, you can see in the waveform how often the messages are being sent.
Using the information in our previous post, we know that the first 4 bytes of these PGN’s are important. The first two provide information on NOx and the next two provide information on the O2 content. Whilst we can’t apply the scale or offset or have it showing the actual values, what we can do is quickly see if the data is changing. You could simply leave the tables as they are, but by using the Index of filter, you can highlight these essential bytes to see if there is activity.
In the above image, you can see the filtered data separating out bytes 0 and 1 and bytes 2 & 3 for the upstream and downstream NOx sensor. It looks like the upstream NOx sensor may have a fault compared to the downstream sensor, as data is changing for the downstream but appears fixed in the upstream. To go one step further, you could then export these tables to CSV and add in the scale and offset for these values.
Further improvements will happen with this filter, but as you can see, there are some real use cases for when this function could help. From this, you could then reduce the size of the decode table to only show the information you require. By clicking fields, you can select and deselect columns of interest.
If you would like to have a play with this new feature, please ensure you have the latest PicoScope 7 Automotive Early Access software installed. There is a file in the waveform library where you can filter the serial decode table.
If you have any feedback on this feature, we would love to hear it. Please send in using the ‘Send Feedback’ button in PicoScope 7 or by emailing support@picotech.com