Conductive Level Monitoring

A conductive level switch is a point level sensor that detects the presence or absence of an electrically conductive liquid at a defined position in a tank, vessel, or pipe It operates by detecting electrical conductivity through the liquid between a sensing electrode and a reference electrode or, in some applications, between the sensing electrode and the conductive metal tank wall. When the liquid reaches the sensing point, it completes the measuring circuit and the switch changes its output state.

Conductive level switches are commonly used for high- and low-level alarms, overfill protection, dry-run protection, and automatic pump or valve control. With no moving mechanical parts, they provide reliable, low-maintenance level detection for many liquids.

A conductive level switch can detect electrically conductive liquids such as water, wastewater, aqueous solutions, acids, alkalis, and many process liquids. It can also be used with viscous conductive liquids if the medium meets the minimum conductivity specified for the instrument. Non-conductive liquids including oils, fuels, and most organic solvents—cannot reliably complete the measuring circuit and therefore require a different level detection technology.

Electrically conductive liquids contain dissolved ions that allow electric current to flow. Examples include water with dissolved salts or minerals, acids, alkalis, and many aqueous chemical solutions. Conductive level switches use this ionic conductivity to detect whether liquid is touching an electrode. 

A conductive level switch detects whether a conductive liquid has reached a defined switching point by evaluating the electrical resistance between a sensing electrode and a reference electrode.

One or more sensing electrodes are installed at the required switching levels inside the vessel. A reference electrode, which normally remains immersed in the liquid, completes the measuring circuit. In a sufficiently conductive, unlined metal tank, the tank wall may serve as the reference electrode. Tanks made of plastic, concrete, or other non-conductive materials require a separate reference electrode.

The associated controller or electrode relay applies a low alternating voltage between the sensing electrode and the reference electrode. When the liquid reaches the sensing electrode, it creates a conductive path through the liquid. Current begins to flow, and the electrical resistance between the electrodes decreases. When the resistance falls below the configured switching threshold, the controller changes the state of its relay or switching output. Alternating voltage is used to minimize electrode polarization, electrolysis, and undesirable oxidation.

When the liquid falls below the sensing electrode, the conductive path is interrupted and the output changes according to the configured switching logic. Depending on the number and arrangement of the electrodes, the system can provide single-point level detection or minimum/maximum level control.

Operating principle of a conductive level switch

The operating principle is based on the electrical conductivity of the process liquid. Unlike a float switch, the conductive measuring system has no moving sensing mechanism.  It detects whether the liquid has created a conductive electrical path between a sensing electrode and a reference electrode. In a suitable unlined metal tank, the tank wall may serve as the reference electrode. This principle enables simple, reliable point-level detection with minimal maintenance.

Conductive level switches are used for point level detection in electrically conductive liquids. Typical functions include high-level and low-level alarms, overfill protection, dry-run protection, and automatic pump or valve control in tanks, vessels, and pipes.

Typical industrial applications include

• Water and wastewater treatment: monitoring water, wastewater, sludge, and chemical dosing tanks.
• Chemical processing: detecting conductive acids, alkalis, and aqueous process solutions
• Food and beverage production: monitoring conductive products in storage, mixing, and process vessels., subject to hygienic and material requirements
• Pharmaceutical production: point level detection in suitable conductive process liquids, subject to hygienic and validation requirements
• Boilers, cooling systems, and industrial utilities: maintaining liquid levels and protecting pumps and other equipment

The process liquid must meet the minimum conductivity specified for the selected switch or controller. Oils, fuels, most organic solvents, and highly purified or deionized water are generally unsuitable unless the device is specifically designed for the application.

For detailed-specific guidance and expert support, consult our engineer to ensure proper selection and long-term performance.

Conductive level switches are generally low-maintenance because they have no moving sensing parts. However, they are not maintenance-free in every application. Inspect the electrodes periodically for scale, deposits, crystallisation, or corrosion, and clean them when necessary. The appropriate interval depends on the process medium and operating conditions. Regular functional testing is recommended, especially for safety-related functions such as overfill and dry-run protection.

Conductive electrodes are commonly installed from the top of a tank or vessel, with each electrode ending at the required switching level. Side or angled installation may also be possible, depending on the model. Follow the manufacturer’s instructions and position the electrodes away from filling jets, heavy turbulence, agitators, vessel walls, and conductive internals that could cause unstable or false switching.

Long rod electrodes may require mechanical support to prevent bending or movement caused by vibration, turbulence, or lateral forces. Any support near an uninsulated measuring section must be electrically non-conductive and chemically compatible. In non-conductive tanks, install a separate reference electrode. Ensure that deposits cannot bridge adjacent electrodes and that the process connection, sealing materials, wiring, and grounding comply with the application requirements.

To select a conductive level switch for reliable, long-term operation, evaluate the process liquid, operating conditions, installation, and required control function. Key selection criteria include.

• Minimum required electrical conductivity of the process liquid: >20 μS/cm, ensure the process liquid is within the conductivity range supported by the device
• Chemical compatibility of all wetted materials, including the electrodes, insulation, seals, and process connection
• Process pressure and temperature, including cleaning and sterilisation conditions
• Electrode configuration, material, coating, length, spacing, and protection against bending or contact with the vessel
• Required number of switching points and control function, such as high-level alarm, low-level alarm, overfill protection, dry-run protection, or minimum/maximum control
• Availability of a separate reference electrode or a suitable electrically connected, unlined metal tank wall
• Installation position, available mounting space, turbulence, foam, deposits, and possible product bridging
• Process connection, electrode type, electrode length, and any required mechanical support
• Compatibility with the controller, relay, PLC, supply voltage, and required output signal
• Ambient conditions, ingress protection, vibration, humidity, and hazardous-area approvals where applicable

Matching these parameters to the technical data of the selected KOBOLD conductive level switch helps ensure dependable switching, long service life, and safe process control. 

To learn more about conductive level switch selection and technical specifications, consult one of our experts or refer to the product documentation.