MATLAB: Do I get a “units are not commensurate” error when adding or subtracting the units ‘C’ and ‘K’

Simscape

I am trying to subtract two temperatures in Simscape. One temperature is in Celsius, and the other is in Kelvin. Why do I get a "units are not commensurate" error when adding or subtracting the units 'C' and 'K'?

Best Answer

For Simscape to be able to subtract two units, the units have to be able to be converted into similar units. For example, you can subtract Celsius from Kelvin because they are both temperatures, and you can convert Celsius into Kelvin (or Kelvin into Celsius).

In Simscape, 'C' represents Coulomb. Because the two units Coulomb and Kelvin cannot be converted into the same unit (they're not both temperatures), Simscape throws the error. Instead, represent Celsius with the unit 'degC'. The list of unit definitions for Simscape can be found at the following link:

https://www.mathworks.com/help/physmod/simscape/ug/unit-definitions.html

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Use the Unit Conversion Block

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That's not user friendly. It would be very annoying to your users and I recommend you DON'T DO THAT, especially since it's not necessary at all. Just convert what they input to upper case with the upper() function, like this:

% Set up the dialog box parameters
prompt = {'Enter temperature:','Enter the temperature scale:'};
dialogTitle = 'Enter parameters';
numberOfLines = 1;
defaultAnswers = {'100','C'};
userResponse = inputdlg(prompt, dialogTitle, numberOfLines, defaultAnswers);
% Extract out individual variables from the user response.
temperature = str2double(userResponse{1})
% Convert to upper case.
EoSI = upper(userResponse{2})

Best Answer

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