sans serif font with siunitx

Question

My students found this problem, which I could not solve. The percent is always printed in the serif font.

Here is a test code:

\documentclass[]{scrartcl}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc} % T1 Schrift Encoding
\usepackage{lmodern}  % Latin Modern
\usepackage[ngerman]{babel}
\usepackage{float}
\usepackage{siunitx}

\sisetup{%
  mode = math,
  detect-family,
  detect-weight,  
  exponent-product = \cdot,
  number-unit-separator=\text{\,},
  output-decimal-marker={\text{,}},
  math-rm=\mathsf,
  text-rm=\sffamily,
}

\begin{document}
\sffamily\noindent
Text \SI{1.23}{\%} and further text.
\begin{table}[H]
\sffamily
\begin{tabular}{ll}
\SI{1.23}{\%} & 1,23\,\%
\end{tabular}
\end{table}
\end{document}

Answer 1

From page 5 of the siunitx manual:

By default, all text is typeset in the current upright, serif math font. This can be changed by setting the appropriate options: \sisetup{detect-all} will use the current font for typesetting.

Thus, just replace the options detect-family and detect-weight in the preamble's \sisetup{...} instruction with detect-all, and your students will be all set.

Incidentally, if you run \addto\extrasngerman{\sisetup{locale=DE}} after loading the babel package with the option ngerman, you don't have to specify the options output-decimal-marker={\text{,}} exponent-product = \cdot, and number-unit-separator=\text{\,} explicitly while loading the siunitx package.

\documentclass{scrartcl}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc} 
\usepackage{lmodern} 

\usepackage[ngerman]{babel}
\addto\extrasngerman{\sisetup{locale=DE}}

\usepackage{siunitx}
\sisetup{detect-all} % note: just one option still needs to be specified

\begin{document}
\sffamily
\SI{1.23}{\%}

1,23\,\%
\end{document}

Answer 2

The problem is that you are assuming that % in \mathsf 'looks' sanserif, but it does not

\documentclass{article}
\begin{document}
$\mathsf{\%}$
\end{document}

Either stick to text mode for units

\documentclass{article}
\usepackage{siunitx}
\sisetup
  {
    math-rm=\mathsf,
    text-rm=\sffamily
  }
\begin{document}
\SI{1.23}{\%}
\end{document}

force text mode for this particular case

\documentclass{article}
\usepackage{siunitx}
\sisetup
  {
    mode = math,
    math-rm=\mathsf
  }
\begin{document}
\SI{1.23}{\text{\%}}
\end{document}

or use the symbolic mode and an appropriate definition

\documentclass{article}
\usepackage{siunitx}
\sisetup
  {
    mode = math,
    math-rm=\mathsf
  }
\DeclareSIUnit{\percent}{\text{\%}}
\begin{document}
\SI{1.23}{\percent}
\end{document}

In all cases, note that extra spacing should not be added to the unit part: there is an automatic space between the number and the unit.

Answer 3

As already have been mentioned the source of the problem is that you typeset the percent in mathmode and assumed that \mathsf{\%} gives a sans serif percent. But the percentchar has mathcode hex 25, the \math... commands affect only chars with math code > hex 7000. You would get the expected result if you would change the mathcode:

\documentclass[]{scrartcl}
\usepackage[T1]{fontenc} 
\usepackage{lmodern} 

\begin{document}
$\mathbf{\% a}\mathsf{\% a} \% a$

\mathcode`\%="7025
$\mathbf{\% a}\mathsf{\% a} \% a$

\end{document}