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Recalculate PRTcalc result


Jakob Pedersen Nov 15, 2021 09:31 AM

Hello

I have a setup where I measure four Pt100 sensors (and ohter sensors as well) with a CR1000 module.

A couple of days ago, I realized that I had made a mistake when filling in the parameters for the PRTCalc instruction for two of the sensors:

What I wrote was this:

BrHalf(RRo(1),1,Autorange,13,Vx2,1,2500,False,0,_50Hz,1,0)
BrHalf(RRo(2),1,Autorange,14,Vx2,1,2500,False,0,_50Hz,1,0)
BrHalf(RRo(3),1,Autorange,15,Vx2,1,2500,False,0,_50Hz,1,0)
BrHalf(RRo(4),1,Autorange,16,Vx2,1,2500,False,0,_50Hz,1,0) 
PRTCalc(RTD_C(1),1,(RRo(1)/(1-RRo(1))),0,1,0) )
PRTCalc(RTD_C(2),1,(RRo(2)/(1-RRo(2))),0,1,0)
PRTCalc(RTD_C(3),1,(RRo(3)/(1-RRo(1))),0,1,0)
PRTCalc(RTD_C(4),1,(RRo(4)/(1-RRo(2))),0,1,0) 

And it should have been this:

BrHalf(RRo(1),1,Autorange,13,Vx2,1,2500,False,0,_50Hz,1,0)
BrHalf(RRo(2),1,Autorange,14,Vx2,1,2500,False,0,_50Hz,1,0)
BrHalf(RRo(3),1,Autorange,15,Vx2,1,2500,False,0,_50Hz,1,0)
BrHalf(RRo(4),1,Autorange,16,Vx2,1,2500,False,0,_50Hz,1,0) 
PRTCalc(RTD_C(1),1,(RRo(1)/(1-RRo(1))),0,1,0) )
PRTCalc(RTD_C(2),1,(RRo(2)/(1-RRo(2))),0,1,0)
PRTCalc(RTD_C(3),1,(RRo(3)/(1-RRo(3))),0,1,0)
PRTCalc(RTD_C(4),1,(RRo(4)/(1-RRo(4))),0,1,0)

Infortunately, I decided not to save the RRo() variable in order to save memory, but is it in any way possible to recalculate the results for sensor 3 and 4?

Any help will be appreciated :-)

Best regards

Jakob Pedersen


aks Nov 15, 2021 09:37 PM

My initial thought is, it is possible in theory. It will take some exercise in  algebra though. Please take a look at Calendar Va-Dusen equation for PRT's. Back claculate the resistance from reported temperatures for say R1 and R3. R1 is correct amd R3 has error in it. You should be able to recalculate R3 using R1 and then go back to calcuate the temperature3. Same exercise for probe 4. If you need help with the math, please email me a small dataset and I will try to work it out.


Jakob Pedersen Nov 16, 2021 12:05 PM

Dear aks

If I could calculate the value of the "source" parameter in the PRTCalc instruction (inverse PRTCalc?), i guess it would be possible to calculate RRo(1), RRo(2) and then RRo(3) and RRo(4) which could then be used for another calculation similar to PRTCalc to get the correct temperatures for RTD_C(3) and RTD_C(4)?

The temperature during the measurements has been above 0 degrees Celcius, so that might help a bit, but I still can´t quite figure out how.

You are most welcome to give it a try - i would be very greatful!

TOA5;CR1000;;;;
TIMESTAMP;RECORD;RTD_C(1);RTD_C(2);RTD_C(3);RTD_C(4)
TS;RN;DegC;DegC;DegC;DegC
;;Avg;Avg;Avg;Avg
13-07-2021 15:40;0;32.12;25.26;26.92;22.94
13-07-2021 15:41;1;32.2;25.34;26.97;23
13-07-2021 15:42;2;32.49;26.15;27.11;23.39
13-07-2021 15:43;3;33.1;26.7;27.43;23.63
13-07-2021 15:44;4;33.59;27.05;27.63;23.71
13-07-2021 15:45;5;33.86;27.1;27.68;23.66
13-07-2021 15:46;6;33.99;27.1;27.74;23.62
13-07-2021 15:47;7;33.99;27.11;27.63;23.51
13-07-2021 15:48;8;33.99;27.2;27.59;23.52
13-07-2021 15:49;9;33.99;27.38;27.51;23.52
13-07-2021 15:50;10;33.99;27.41;27.45;23.48
13-07-2021 15:51;11;34.01;27.41;27.46;23.4
13-07-2021 15:52;12;34.17;27.64;27.46;23.48
13-07-2021 15:53;13;34.31;27.72;27.47;23.46
13-07-2021 15:54;14;34.46;27.95;27.54;23.51
13-07-2021 15:55;15;34.63;28.26;27.54;23.59
13-07-2021 15:56;16;34.9;28.46;27.62;23.64
13-07-2021 15:57;17;35.13;28.68;27.73;23.71
13-07-2021 15:58;18;35.26;28.96;27.75;23.81
13-07-2021 15:59;19;35.44;28.99;27.76;23.75
13-07-2021 16:00;20;35.58;29.26;27.82;23.87
13-07-2021 16:01;21;35.74;29.27;27.85;23.83
13-07-2021 16:02;22;35.9;29.47;27.85;23.87
13-07-2021 16:03;23;35.9;29.59;27.84;23.86
13-07-2021 16:04;24;35.93;29.59;27.85;23.83

Best regards

Jakob


Jakob Pedersen Nov 26, 2021 03:12 PM

This post is under review.

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