High Temperature Liquid Level Sensor: Electrode Level Control for Conductive Liquids

Level control in steam boilers, booster sets and hot process tanks is demanding because of high temperature, pressure and sometimes dirty media. A high temperature liquid level sensor detects the level of conductive liquids using electrodes and an external level relay; it has no moving parts and is an economical, durable solution.

What Is a High Temperature Liquid Level Sensor?

The sensor consists of one or more stainless steel electrode probes fitted in a high-temperature-resistant insulating body. When the electrode tip touches the liquid, a small current flows through the liquid between the electrode and the tank shell (or a reference electrode). The level relay detects this current and switches its contact to control a pump, valve or alarm.

Working Principle

1. Liquid reaches the electrode: The conductive liquid completes the circuit between the electrode tip and the tank shell.
2. Current detection: The level relay applies a low-voltage alternating current (AC) to the electrode and detects the weak current through the liquid.
3. Signal output: The relay amplifies this current into a contact output.
4. Liquid recedes: When the level falls below the electrode tip, the circuit opens and the relay returns to its initial state.

Using AC prevents electrolysis and polarisation on the electrode surface and extends electrode life. Several electrodes of different lengths allow multiple level points, such as pump start, pump stop and alarm, to be controlled through a single connection.

Advantages

• No moving parts: No float or mechanism to wear or stick; low maintenance.
• High temperature capability: Body and insulation materials rated for different high temperatures and pressures depending on the model.
• Suits difficult media: Works with conductive liquids containing solids, of high viscosity or low density; unaffected by density.
• Adjustable length: Electrode length can be cut or extended to suit tank depth; on some models the electrode probe is supplied separately.
• Economical, easy installation: Quick threaded connection.

Applications

• Steam boilers: Feedwater pump control and level alarms
• Booster sets: Pump protection and control based on tank level
• Conductive liquid tanks: Process and storage tanks
• Harsh conditions: Dirty or particle-laden liquids where moving parts can cause problems

For low-water safety cut-off on steam boilers, approved safety electrodes and self-monitoring level relays complying with the relevant boiler standards must be used.

Frequently Asked Questions

Conclusion

High temperature liquid level sensors provide reliable, economical and long-lasting level control without moving parts in boilers, booster sets and process tanks containing conductive liquids. Selected together with the right electrode length and level relay, they perform well even under harsh conditions. See our level control devices page for other options.