  An algorithm of the ensemble pulsar time based on the Wiener filtration
method has been constructed. This algorithm has allowed the separation of the
contributions of an atomic clock and a pulsar itself to the post-fit pulsar
timing residuals. The method has been applied to the timing data of the
millisecond pulsars PSR B1855+09 and PSR B1937+21 and allowed the filtering out
of the atomic scale component from the pulsar phase variations. Direct
comparison of the terrestrial time TT(BIPM96) and the ensemble pulsar time
PT$_{\rm ens}$ has displayed that the difference TT(BIPM96) -- PT$_{\rm ens}$
is within $\pm0.4 \mu$s range. A new limit of gravitational wave background
based on the difference TT(BIPM96) -- PT$_{\rm ens}$ was established to be
$\Omega_g {\rm h}^2\sim 10^{-10}$.
