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Concrete Maturity Calculation Help
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August 2, 2020
12:16 pm
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August 2, 2020
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I am a Civil Engineer and has very limited knowledge about IOT.
I have set up a DS18B20 temperature sensor sending data to Thingspeak via a ESP8266 MCU.

The sensor is placed inside a concrete cube, measuring its setting temperature.

The measured temperature, lets call it Ta is to be used in the following equation.

M(t) = ∑ (Ta-Td) ∆t

Where M(t) – Maturity at age t (°C-Hrs)
Ta - Average Temperature in ° C
Td - Datum Temperature in ° C and is set to 0
∆t - Time Interval

As you can see Ta is the only measured data along with time interval between 2 readings (set to 30 minutes). I wish to create a MATLAB analysis wherein the measured temperature from the first channel is used to calculate M(t).
But I dont know how to code the above formula as it requires to add the calculated M(t) once every 30 minutes and tell the updated value.

I would greatly appreciate your help.

August 19, 2020
11:50 am

Forum Posts: 885
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March 7, 2017
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Set up the following MATLAB analysis

%read temp values from channel
myTimeTable = thingSpeakRead(channelID, 'ReadKey', ''READAPIKEY", 'outputFormat','Timetable', 'numMinutes',1000);

%I presume your average means average temperature over the local time segment, so just the temperature value written.
% If we need to average over several values, that can be done as well.
timeDurations = diff(myTimeTable.Timestamps)
sumElements = timeDurations * myTimeTable.TEMPERATUREFIELDNAME; %replace TEMPERATUREFIELDNAME with your temp field
total = sum(sumElements);

Total will then be in units of scaled durations - i.e. hours and minutes times temperature. There are MATLAB functions to convert it to seconds or whatever units you like.

Then set up a timecontrol to call this code at whatever interval you like.

then you can even add a ThingSpeakWrite at the end to write the output to another channel each time the calculation runs.

FYI MATLAB answers is the preferred location for ThingSpeak support.

September 4, 2020
9:14 am
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Forum Posts: 1
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September 4, 2020
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Hello. Your advice helped me .thanks

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