Electrostatic field measurements taken in Bogotá, Colombia, during thunderstorms in November (the rainy season due to inter-tropical confluence zone over central Colombia) were used to study the performance of an isolated electric field sensor and analyse its most important operational characteristics. The distances from each flash to the studied sensor were obtained by using the Colombian lightning location system. The ΔE cf distance ratio led to defining a charge model which could be used as a reference for calibrating other electrostatic field sensors to be used as lightning warning systems.