Capacitance level sensors, also called RF or radio frequency sensors, are sensors that detect the level of a liquid or substance based on the differences between the frequency the sensor emits with the amount of AC circuit current the sensor receives back from the material inside the container. The differences in the two frequencies can identify the level of the liquid or material inside the container. Capacitance level sensors are highly useful in measuring the level of critical materials, such as when a liquid has a chance of overflowing or dropping below a safe level.
The capacitance sensor has two base conductors that are isolated from one another with a non-conductor. The conductors can vibrate at two different frequencies. When this occurs, the capacitance can hold an electrical charge for a short period. The capacitance can read the level of the material or liquid inside a container by applying an RF frequency to the container wall and the conductive probe at the same time. The differences in the frequency that comes back from the initial signal can identify the level of the material inside the container in relation to the top of the container. The less liquid is in the container, the less conductive the probe becomes, which signals a drop in the liquid level.
Most capacitance sensors are made from simple stainless steel probes, while others contain a small housing or coating to protect them from the material inside the container, such as a corrosive chemical. Side wall probes vary from 7 to 16 inches in length, while vertical probes can vary between 4 to 50 feet. Some probes require an addition of a metal string with a weight to extend the reading throughout the height of the container.