Re: [rrd-users] Intermittent data causing stepped graphs

[Simon Hobson]

jamiedg  wrote:

> Recently though I've hit a problem that maybe someone can help with;
> My temp sensors would normally save data at least once a min which worked
> fine, but to extend battery life the newer sensors are only transmitting
> data when the temp changes or at most every hour. This causes intermittent
> data causing the charts to sometimes have a stepped output.
> 
> 
>  
> 
> When I post the same data to the cloud service EmonCMS I get a more smoothed
> output.
> 
> 
>  

The obvious observation is that the latter is wrong FOR THAT DATA. The data you 
are feeding in doesn't have the data to show a sloping line, so drawing a 
straight line between the points is strictly speaking incorrect FOR THAT DATA.

Your real problem is that the data itself is stepped. When you say that the 
sensor only sends data when the temperature changes, it presumably has some 
quantisation - it appears to be reporting to a resolution of 0.1˚. I suspect 
that the older sensors are reporting to a higher resolution - eg if it reports 
to 0.01˚ then you'd not see the steps as they'd be smaller than the pixels on 
the graph, both in the Y axis due to the resolution, and in the X axis due to 
the frequent reports.

Do you still have any of the old sensors ? If so then I'd suggest comparing the 
raw data. My guess is that the old ones report to a higher resolution, which 
combined with frequent updates will give you a smooth graph. The new ones are 
almost certainly quantising to a much lower resolution (otherwise there'd be 
little or no battery saving) which is what's giving you your problem.


> If the data is Undefined I use the Prev value (sen3,UN,PREV,sen3,1,*,IF)

That is probably wrong as well. You are explicitly telling RRD to draw a flat 
line there.

> Can anyone please offer any suggestions or help to smooth the stepped graph
> output.

Fix the input ?

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[rrd-users] Intermittent data causing stepped graphs

[jamiedg]

I've been using RRD for sometime to chart temp sensor data and have found it
to be one of the best charting tools , the charts generate in the blink of
an eye and use only minimal resources.
Recently though I've hit a problem that maybe someone can help with;
My temp sensors would normally save data at least once a min which worked
fine, but to extend battery life the newer sensors are only transmitting
data when the temp changes or at most every hour. This causes intermittent
data causing the charts to sometimes have a stepped output.


 

When I post the same data to the cloud service EmonCMS I get a more smoothed
output.


 

Because the data could change every 30s, I have the step at 30 but the
heartbeat at 3600 and the xff at 20%

See the below rrd create script:

rrdtool create sen3step30.rrd \
--step 30 \
DS:Sen3:GAUGE:3600:U:U \
DS:Temp3:GAUGE:3600:U:U \
RRA:AVERAGE:0.2:1:1440 \
RRA:AVERAGE:0.2:6:1440 \
RRA:AVERAGE:0.2:36:1440 \
RRA:AVERAGE:0.2:144:1440 \
RRA:AVERAGE:0.2:1008:1440

I use the below chart script:
rrdtool graph /var/www/graphs/graph03t.png --start end-6h --height 150
--width 700 --end now --slope-mode --title "Temp for last 6h"
--vertical-label Temp --alt-autoscale-max\
DEF:sen3=/home/pi/cc/sen3step30.rrd:Temp3:AVERAGE   
CDEF:cdefsen3=sen3,UN,PREV,sen3,1,*,IF   
LINE3:cdefsen3#9A2EFE:'Conservatory Temp'  \

If the data is Undefined I use the Prev value (sen3,UN,PREV,sen3,1,*,IF)

Can anyone please offer any suggestions or help to smooth the stepped graph
output.

rrdtool -v = RRDtool 1.4.7  

thanks and regards,
jamie



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