If I end a sentence with Ph.~D. how do I tell LaTeX that this IS a sentence end

Question

So, LaTeX automatically knows that "E. Xample" is a name and doesn't add a full sentence ending space to the end of it, right? But if I'm writing Ph. D. I want to put in a marker, so it knows that Ph. isn't the end of a sentence. Ph.~D. or Ph.\ D. depending on if I want it to be able to line break in the middle or not. But what do I do if I'm ending a sentence with Ph. D.? For example: "over the course of my Ph.\ D."

MWE:

\documentclass[]{article}
\begin{document}
\noindent \textit{This space feels wrong as there is too much space between the Ph.\ and D., then not enough after the D:}

\ldots scientific equipment over the course of my Ph.~D. 
In addition to gathering all my own data on the X-ray diffractometer\ldots

\vspace{\baselineskip}
\noindent \textit{Now there is WAY to much space between sentences! I thought quad was the normal space between sentences. }

\ldots scientific equipment over the course of my Ph.~D.\quad 
In addition to gathering all my own data on the X-ray diffractometer\ldots 
\end{document}

Answer 1

You add \@ before the period.

\quad is a huge space. It's traditionally one em, the amount of space equal to the current type size although if I recall correctly, the cmbx* defines an em to be wider.

Answer 2

Another way is given in The TeXbook, Exercise 12.6.

What can you do to make TeX recognize the ends of sentences that do end with uppercase letters (e.g., ‘... launched by NASA.’ or ‘Did I?’ or ‘... see Appendix A.’)?

There are several ways; perhaps the easiest are to type ‘\hbox{NASA}.’ or ‘NASA\null.’ (The \null macro is an abbreviation for ‘\hbox{}’.)

So Ph.~D\null. works, actually quite the same way as Ph.~D\@. does, resetting the space factor to 1000. I suppose the latter is more LaTeX'y just like anything that contains the character @.