I am trying to measure some flow temperatures in and out of my boiler. I have a couple of EmonTH units with external probes attached to the pipework. However I’m seeing really odd behaviour when I try and graph the feed data, and I wanted to see if anyone could recommend some ideas as to what might be going on?
The two EmonTH units are next to each other in a cupboard, and are about 7m from the EmonPi. I see what look like feeds being received every minute or so (with good signal strength) on EmonCMS…however there are loads of missing data when I try to graph the feeds. I’m wondering if I have maybe miss-configured my EmonPi or EmonCMS in some way? Is 7m too far for a reliable connection between the EmonTH devices and the EmonPi?
Assuming these EmonTH are operating in the 433Mhz band, I took a quick look with a spectrum analyzer…but didn’t see very much traffic at all…and no real indication of interference in that location
How have you set up the Feeds? - If the feed interval is less than 1 minute, it will contain NULLs between readings. The graph software picks points when there are too many to fit in a pixel, and if it happens to land on NULLs, you get missing data. Your Feed interval should be not less than 60 s.
What happens then is the emonTH sends its data at about 55 s intervals, so after a while, it loses a reading because two arrive inside the same one-minute slot. But if there’s a processing delay in emonCMS, a sample is still not delayed enough to miss its slot, so you avoid having NULLs in the database.
(Were you to set the Feed to 2 min, say, every other reading would get overwritten by the next one; 4 overwritten by the 5th for 5 min, and so on.)
Robert…thank you for highlighting that. It does look like one of the feeds was set to 10s refresh. Is there an easy way to change it…as I had a quick look at EmonCMS, but couldn’t see an obvious way to change the refresh rate
There isn’t, because of the way Feeds work. You can only delete the Feed and start afresh, losing the data recorded so far in the process.
(The Feed calculates the time for each record from the start time and interval × record number, it’s not stored in the fixed interval Feed, but it is in the variable interval Feed.)
I’ve deleted and recreated the feed, and data seems to be coming through now. At least I haven’t got a hardware issue, which was my main worry! Thank you so much for pointing me in the right direction
