Newbie question: Lookup tables

Grafana Dashboards
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  • Grafana version: V9.2.0 on Windows
  • Apology up front - new to Grafana so will likely be using the wrong nomenclature, so please be considerate!
  • I’m looking for a way to use a value pulled from influx, interpolate a result from a table, compare to a second value from influx & give a text output.
  • Specifically I have a fluid pressure & temperature, want to use the pressure to look up the saturation temperature in a table to output if the fluid temperature is above/around/below that.

I have it working nicely in Excel, but would prefer to get a live panel on the go on my dashboard:

  • =IF(E7>Q7,“Above”,IF(E7<Q7,“Below”,“Around”))
    • E7 = Fluid Temp.
    • Q7 = FORECAST($D7,O7:P7,M7:N7) ← Saturation Temp.
      • D7 = Fluid Pressure
      • M7:N7 = Sat. table pressures above & below D7 (done with index matching to the saturation table)
      • O7:P7 = Sat. table temps associated with M7:N7
2

Welcome,

Is this table in a database and what database type is it in?

1 Like
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It’s not anywhere other than excel on my desktop just yet - literally at square one for knowing where to go with this. Did my best to look it up but haven’t struck upon the right terminology to get an answer!

4

no worries, we can provide you some guidance. So do you currently have influx installed with data in it?

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Yes, I can pull the two required data feeds live

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since we do not have access to your influx db please post some sample data as csv here like following

date,metric,value,
2022-10-18 08:00:00,pressure,23
2022-10-18 08:00:00,temperature,123

this is just a sample so you will have to fill in the rest as it is in your influxdb.

Also are you using flux queries or influxql?

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Time,Pressure,Temperature
1666084810000,7.5,9.56
1666084820000,7.5,9.57
1666084830000,7.6,9.58

I don’t know on flux vs. influxql - is there an easy way to tell?

1 Like
8

what version of influxdb are you using? what does the query you are currently look like?
Also those timestamps, what precision are they?

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Typical query: image

Values are logged every 10 seconds, but as I’m pulling from grafana (rather than influx directly) it tends to skew that in the data I pull, but what I want is a calculation live in Grafana so I’m not bothered by that.

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ok so you indeed using flux query language.

Please answer this

Also those timestamps, what precision are they?

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Values are logged every 10 seconds

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precision means, millisecond, seconds, minutes?

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It might be a bit of a tangent, but how does the precision affect what I’m after? I can’t say for certain but it’s in the second to millisecond range. So long as the output I’m after is accurate to within 5 minutes I’m happy (I’m looking at weeks worth of data that changes slowly).

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doesn’t affect you at all, but it affects us being able to help you. as I said in the beginning we don’t have access to your data so we need to spin up a copy of your data in our environment.

15

Almost reassuring it’s not quite as simple as “obviously you do this”!

Working an example with the numbers above, I think the process comes down to:

  1. Storing a table in Grafana
  2. Interpolating values
  3. Running the output logic

Fluid measurements from influx:

T P
7.5°C 9.56 bar

Saturation data (from TBC):

T P
5°C 9.34bar
6°C 9.63bar
7°C 9.93bar
8°C 10.23bar
  • Tsat @ 9.56bar comes out as 5.76°C
  • T = 7.5°C
  • T > Tsat
  • Output = “Above”
1 Like
16

I think you will have to use a Map to store your fluid pressure & temperature data in a table in InfluxDB.

For the linear interpolation, Influx has that covered too.

How do you envision your data to appear in Grafana? In a simple table of values? Maybe share what your Excel model looks like.

2 Likes
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Thanks Grant - it looks like I’ll have to commit and get my head around a little bit of programming!

I hadnt envisaged anything much fancier than a state timeline.

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I’ve managed to make some progress, but have hit a snag I can’t get past:

I’ve managed to upload a CSV with the pressure values I’m after, using a field tag for the associated temperatures. This way I’ve successfully pulled the pressure value by looking up the temperature tag - e.g, look up the field tagged “7”, it pulls the pressure “9.93”.

Separately I can pull the live value of the temperature reading “TL1 = 7.5” & round it down to “TL1int = floor(TL1) = 7”.

The hurdle I can’t get past is then using “TL1int” in place of “7” typed manually to pull “9.93”. I’m thinking if this works I’ll then be able to see a time history of the different pressure values with changing temperature readings. I’ve two thoughts on the issue:

  1. I shouldn’t be using field tags like that
  2. I need to convert the “TL1int” from a number to text or other format