# Units for constants in simscape custom module

12 views (last 30 days)
Steven on 3 Feb 2017
Commented: Steven on 6 Feb 2017
I have a constant that I have declared in the variables section. I'm assuming that everything needs units. Some papers use constants that use equations with units that don't match (on one side of the equation its a constant and on the other side might be V/K)
variables(Access=private)
cm = { 0, '' };
i = { 2, 'A' };
V1= { 0, 'V' };
T1 = { 0, 'K' };
end
in the equations section if I mix up the units will it throw an error?
equations
i == V1*T1;
end
is there some way to have a unitless constant that doesn't have units?
equations
cm == V1*T1;
end

Steven on 6 Feb 2017
Sure enough, Got an error: Provided units 'Ohm' and 'K' are not commensurate
Steven on 6 Feb 2017
Found some help : https://www.mathworks.com/help/physmod/simscape/lang/declaring-domains-and-components.html#bruso4j-1
To declare a unitless parameter, you can either use the same syntax:
par1 = { value , '1' };
Steven on 6 Feb 2017
This doesn't solve my problem right now however, because I have Kelvin/Kelvin and its not going to unitless. Example:
nodes %conserving ports
Ta = foundation.thermal.thermal; % H:top
Tb = foundation.thermal.thermal; % C:bottom
end
variables
R = {334, '1'};
end
parameters
cTemp = {3.2342, '1'};
end
equations
R == (Th.T - cTemp)/Th.T;
end
This will not compile. Even changing R and cTemp to units of K will not compile

Nirja Mehta on 6 Feb 2017
Assign '1' as the unit of "cm".

#### 1 Comment

Steven on 6 Feb 2017
That compiles, but I can't combine a that is set with R = {334, '1'}; value with any other unit in an equation so it doesn't have that much use. I need a true unitless value that will compile