How to prevent dry burning when using pipe electric heater

If a ducted electric heater experiences dry-burning during operation, it can damage the auxiliary heater or lead to more serious consequences. How can this be prevented?
What is dry-burning? Dry-burning occurs when the auxiliary heater's water tank is empty or contains less than the specified amount of water. This means that dry-burning is not a predetermined operating state but rather an incident during system operation, a malfunction. If this condition persists, it can have more serious consequences. With the rapid development of ducted electric heaters, ducted electric heaters can now prevent continuous dry-burning.
Preventing continuous dry-burning means that if heating is started without or without water, the system can be shut down and power cut off before any consequences occur. Before this condition becomes apparent, power cannot be continued, regardless of the temperature controller's operation or whether the system power supply is disconnected.

Induction heating in ducted electric heaters utilizes the thermal effect of induced currents (eddy currents) generated by an alternating electromagnetic field in a conductor to heat the conductor itself. Depending on the heating process requirements, the AC power supply used in induction heating can have frequencies ranging from industrial frequency (50-60 Hz), medium frequency (60-10,000 Hz), and high frequency (above 10,000 Hz). Industrial frequency power is the most commonly used AC power source in industry, with the industrial frequency used in most countries being 50 Hz. The voltage applied to the induction device by the industrial frequency power supply for induction heating must be adjustable. Depending on the power of the heating equipment and the capacity of the power grid, a high-voltage power supply (6-10 volts) can be used through a transformer, or the heating equipment can be directly connected to a 380-volt low-voltage grid.

Medium-frequency power supplies have long been based on medium-frequency generator sets. These consist of a medium-frequency generator and a drive asynchronous motor. The output power of these units generally ranges from 50 to 1,000 kilowatts. With the advancement of power electronics technology, medium-frequency power supplies using thyristor inverters have been adopted. These medium-frequency power supplies use thyristors to convert industrial-frequency AC power into DC power, and then convert the DC power into AC power of the required frequency. Due to their small size, light weight, quiet operation, and reliable operation, these inverters have gradually replaced medium-frequency generator sets. Typically, a high-frequency power supply first uses a transformer to boost a three-phase 380-volt voltage to a high voltage of approximately 20,000 volts. Thyristors or high-voltage silicon rectifiers are then used to rectify the industrial-frequency AC power into DC power. Finally, an electronic oscillator tube converts the DC power into high-frequency, high-voltage AC power. The output power of high-frequency power supply equipment ranges from tens of kilowatts to hundreds of kilowatts.

The object being inductively heated must be a conductor. When high-frequency AC current passes through a conductor, it produces a skin-tilt effect, where the current density is higher at the surface and lower at the center.

Induction heating can achieve uniform heating of the entire object and surface; it can even melt metals. At high frequencies, the shape of the heating coil (also known as the sensor) can be changed, allowing for localized heating.