Creating a chemical solution with water and chlorine
Is your measuring instrument made for measuring chloride or chlorine ? It is not the same. In your first sentence, you speak of chloride. Later on you speak of chlorine. Anyway, the best thing to do is to buy a bleach solution. The amount of chlorine is printed on the label. It is often $14$% chlorine $\ce{Cl_2}$. By diluting a sample (maybe $1$ mL) of such a solution in 1 liter water, you obtain a solution $0.14$ gram chlorine $\ce{Cl_2}$ per liter, and you can dilute it still more.