  The KArlsruhe TRItium Neutrino (KATRIN) experiment aims to measure the
neutrino mass with a sensitivity of $0.2\,eV$ ($90\,\%$ CL). This will be
achieved by a precision measurement of the endpoint region of the
$\beta$-electron spectrum of tritium decay. The electrons from tritium
$\beta$-decay are produced in the Windowless Gaseous Tritium Source (WGTS) and
guided magnetically through the beamline. In order to accurately extract the
neutrino mass the source properties, in particular the activity, are required
to be stable and known to a high precision. The WGTS therefore undergoes
constant extensive monitoring from several measurement systems. The Forward
Beam Monitor (FBM) is one such monitoring system. The FBM system comprises a
complex mechanical setup capable of inserting a detector board into the KATRIN
beamline inside the Cryogenic Pumping Section with a positioning precision of
better than $0.3\,mm$. The electron flux density at that position is on the
order of $10^{6}\,s^{-1}mm^{-2}$. The detector board contains a hall sensor, a
temperature gauge, and two silicon detector chips of
$\textit{p}$-$\textit{i}$-$\textit{n}$ diode type which can measure the
$\beta$-electron flux from the source with a precision of $0.1\,\%$ in less
than a minute with an energy resolution of FWHM = $2\,keV$.
