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I’m confused… when I pull up the preferences I’m given a choice of MAX, 1s, 10s, and 1m. What is this interval? How is it different from the sample rate (125Hz, 250Hz, 500Hz, etc)? Which setting applies to logging? Why isn’t there anything about it in the documentation?
Hi Julia,
Sorry, that difference should be made clear.
In the meter preferences where it says MAX, 1s, 10s and 1m, those are logging intervals. So if you leave it unattended with an SD card in and LOGGING set to “on” it will wake and take a sample every 1s, 10s, 1m.
The 125Hz, 250Hz, 500Hz setting is for the sample frequency with which the meter fills its internal sample buffer in RAM. The user should not need to mess with this setting, but some power users who use the “buffer mode” a lot like having manual control over it.
Hope this helps, best
~JamesThanks, James, that answers my question :)
Hi, I’m finding that the log records a sample every 2.304 seconds (0.434hz) when not connected to an iPhone. This changes to 0.305 seconds (3.279hz) when it is. Regardless, it doesn’t seem to line up with the 1s, 10s, 1m, options in the app. Could you elucidate on this?
Thanks,
Chris DeckardHi Chris,
No problem – sorry it’s a little confusing but your meter is behaving correctly.
- When logging is enabled, the sample is logged to the SD card every time the meter completes a sample.
- When the meter is connected to the phone, it is sampling continuously. This is why you see a sample in the log ever .3 seconds.
- When the meter is disconnected with logging is enabled, it does the following:
- Sleep for the selected logging interval (1s in your case)
- Wake up, allow the ADC to settle (takes about a second on PCB RevI)
- Run a sampling cycle (takes about .3 seconds if you have the default settings for measuring DC selected)
- So the total time between samples will be about 2.3 seconds even though the logging interval selected is only 1s.
I hope this explains it. Best
~JamesThis is more than confusing, it’s just plain wrong imo. If I select a 10s interval and monitor a process for 1,000 seconds, I expect to get 100 data points, evenly spaced at accurate 10-second intervals in my CSV file, regardless of whether it’s connected to a phone or not.
Of what use is data logging if the recording interval is not known and constant? Sometimes 0.3s and other times “about 2.3s”?!? Please tell me what I’m missing and how this makes any sense at all.
Also, it’d be better (imo) if each time a new logging session is started a new CSV file would be written to the card, rather than appending the new session to one giant log file. Or at least make this a user-selectable option.
Hi Julia,
On reflection, I think you’re right… 2.3 seconds is not an approximation of 1 second. I fell in to the trap of thinking from the firmware perspective and letting the user perspective slide too much. I think of the sampling interval as the sleep time between samples, disregarding the sampling time itself, but the majority of users will have your expectation. Consider “making time between samples in log samples correspond to selected sampling time” on the to-do list.
Regarding when to start a new logging session – right now the firmware should generate a new log file every time you switch logging off and on again. Is this what you mean?
Thanks again, you’ve given a lot of feedback over the course of the project and it’s been really helpful!
~James
