Current sense transformers are designed and used in a different way than power transformers. Typically with the secondary winding having far more windings than the primary, these devices are used to detect line current for AC sensing and measurement applications. The key parameter for current sense transformers is their current sense rating. In this simple schematic, the current passes from the primary side at a particular frequency to the secondary side. The turns ratio of the transformer determines the output voltage on the secondary. By connecting a resistor, and measuring the voltage across it, ohms law can be used to calculate the current in the secondary winding. This method does not give a precise result, but it is a less expensive and simpler way to detect current flowing through circuits in applications which do not require high levels of accuracy.