如图,射线\(OA\),\(OB\)所在的直线的方向向量分别为\( \overrightarrow{d_{1}}=(1,k)\),\( \overrightarrow{d_{2}}=(1,-k)(k > 0)\),点\(P\)在\(∠AOB\)内,\(PM⊥OA\)于\(M\),\(PN⊥OB\)于\(N\);
\((1)\)若\(k=1\),\(P( \dfrac {3}{2}, \dfrac {1}{2})\),求\(|OM|\)的值;
\((2)\)若\(P(2,1)\),\(\triangle OMP\)的面积为\( \dfrac {6}{5}\),求\(k\)的值;
\((3)\)已知\(k\)为常数,\(M\),\(N\)的中点为\(T\),且\(S_{\triangle MON}= \dfrac {1}{k}\),当\(P\)变化时,求动点\(T\)轨迹方程.