COW-KNI/A JOLA hanging electrode

Description

The COW-KNI/A JOLA floor electrode signals via an electrode relay the presence of a liquid medium due to, for example, a burst pipe. Floor electrodes are designed for use in dry rooms.

COW-KNI/A with integrated galvanic separation:

• prevents the electrode circuits from interfering with each other
• prevents the formation of earth loops when more than one detector is connected to a common power supply circuit.

Capacitive suspension sensors COW -… must only be used in normally dry environments. They must be installed with the sensor facing downwards.

The stainless steel hollow roller is integrated in a capacitive suspension sensor type COW -…. A stainless steel housing as screening electrode and a hollow inner cylinder as measuring electrode form 1 sensing capacitor. As soon as a non-conductive liquid flows into the space between the housing and the inner cylinder, the capacitance between the housing and the inner cylinder shall change and the switching state of the leak detector shall also change. If a conductive liquid is present, the housing and the inner cylinder are conductively bridged, which also results in a change in the on state of the leak detector.

Capacitive measurement principle

The capacitive measuring principle is mainly used to detect electrically non-conductive (insulating) liquids, but can also be used to detect electrically conductive liquids.

Electrically non-conductive liquids are usually organic liquids, similar to oils and solvents. The electrode assembly is a capacitor and the dielectric is air or liquid. The dielectric constant of air is 1. The dielectric constant of the liquid to be detected is higher. For our capacitive sensors, the dielectric constant must be greater than 2 (CPE type) or 1.8 (OWE and COW type).

The capacitive leak detector recognises a change in the dielectric constant of the measuring capacitor and an alarm signal is triggered. The design of the measuring capacitor allows direct mounting on the ground and generally excludes the possibility of interference effects due to different substrates. The capacitive leak detector shall have an integrated electronic evaluation unit with galvanically isolated circuits. This prevents sensor circuits from interconnecting and forming earth loops if more than one of these leak detectors is connected and where the fluid detected is conductive.

Features COW-KNI/A

• Design: leak detector with evaluation electronics as initiator for NAMUR circuit
• Detection capacitors: stainless steel housing as screening electrode and inner cylinder as measuring electrode form 1 detection capacitor
• housing: 316 Ti stainless steel with PTFE insulator
• electrical connection: two-wire connection via 2 x 0.75 connecting cable, 5 m long, longer connecting cable on request; halogen connecting cable available on request
• supply voltage: only for connection to extra low voltage SELV or PELV! (see datasheet)
• output signal: impressed current signal in the power supply circuit
• operation: quiescent current principle
• switching state in case of cable break: I < 0.2 mA
• switching condition both sensing capacitors are activated: I ≤ 3 mA
• switching condition both sensing capacitors are not activated: I ≥ 1 mA
• switching status in case of short circuit or wrong polarity: I > 6 mA
• galvanic isolation: only for connection to extremely low voltage SELV or PELV! voltage resistance> 500 V between capacitor circuit, supply circuit and output circuit
• max. no-load voltage across the sensing capacitors: 5 Veff 200 kHz (safety extra-low voltage SELV)
• max. short-circuit current on sensing capacitors: 0.2 mA
• min. dielectric constant of the liquid to be detected: 1.8
• temperature range: – 20 °C to + 60 °C

For more technical information, please refer to the datasheet attached under the Documentation tab.

COW-KNI/A: Fuel oil leak detection