已知\(F _{1}\)，\(F _{2}\)分别为椭圆\(C： \dfrac {x^{2}}{a^{2}}+ \dfrac {y^{2}}{b^{2}}=1(a > b > 0)\)的左、右焦点，\(B\)为椭圆\(C\)短轴的端点，若\(\triangle BF _{1} F _{2}\)的面积为\( \sqrt {2}\)，且\(\cos ∠F_{1}BF_{2}= \dfrac {1}{3}\)．
\((1)\)求椭圆\(C\)的方程；
\((2)\)若动直线\(l\)：\(y=kx+m\)与椭圆\(C\)交于\(P(x _{1} , y _{1} )\)，\(Q(x _{2} , y _{2} )\)，\(M\)为线段\(PQ\)的中点，且\(M\)在曲线\( \dfrac {2x^{2}}{3}+y^{2}=1\)上，设\(O\)为坐标原点．求\( \dfrac {\sin ∠OPQ}{\sin \angle POM}\)的范围．