Difference of min and max over $__interval

Grafana InfluxDB
1

Hello,

I have the value of my Electricity counter (kWh) in a series.
Now, I’d like to show in a pie-chart the power consumed over $__interval.

With a fixed time of -say- a day, this query works:
SELECT max(“value”)-min(“value”) FROM “eg.Wohnzimmer.Hauptlicht.Verbrauch” WHERE $timeFilter GROUP BY time(1d) fill(previous)

But when using
SELECT max(“value”)-min(“value”) FROM “eg.Wohnzimmer.Hauptlicht.Verbrauch” WHERE $timeFilter GROUP BY time($__interval) fill(previous)

I get a way to small value (0.67 vs expected ~5). When formating as a timeseries, I can see that my query does not create one value, but many values (differences)

image
image1820×547 47.6 KB

So, I seem to have differences now between each two datapoints in the interval. I try to sum them up with

SELECT cumulative_sum(max("value")-min("value"))  FROM "eg.Wohnzimmer.Hauptlicht.Verbrauch" WHERE $timeFilter GROUP BY time($__interval) fill(previous)

(I tried sum as well)
But that gives me “No data”

So, finally I tried:

SELECT max("value") - min("value") FROM "eg.Wohnzimmer.Hauptlicht.Verbrauch" WHERE $timeFilter

It gives me a value of 4.5

Is this what I want?

Greetings,
Hendrik

2

IMHO you will want to use DERIVARE function which will calculate rate from the counter. Search this forum or internet - it seems to be FAQ.

3

Hello,

the derivative would have the Unit kW. That is the Power. I want the work (kWh).
Thus, I do not need a derivative or an Integral (latter I would need if I had the Power and would want the Work, and that is what I always find when searching).

I just need the difference of my counter at the beginning of the interval and the end of the interval.

Regards,
Hendrik

4

Hi, Maybe this could help you
https://localhost:3000/t/problem-with-influxdb-and-energy-monitor/26072/6

5

Why not SPREAD()?

SPREAD()

Returns the difference between the minimum and maximum field values.

2 Likes
6

I had the same issue as the topicstarter, SPREAD solved all of my problems!

7

Anyone any luck with getting a spread based on the interval?

ref Problem with influxdb and energy-monitor - #9 by patvdleer

1 Like
8

Nice! Exactly the answer I was looking for.