Baumer’s New Capacitive Level Sensor Unhindered by Film Adhesion

Baumer recently announced the release of the new PL240 capacitive level sensor. The PL240 is a non-contact sensor used to determine the level of liquid in a tank, capable of sensing through thick plastic tanks. One of the highlighted features of this sensor is its resistance to false readings arising from thin films of liquid that may form along the walls of the tank. The primary markets for this sensor will be the food and beverage manufacturing industries, as well as some chemical processing industries.

 

Advantages of Contactless Sensing

The PL240 is a non-contact, capacitive sensor. Because the sensor never contacts the liquid, it is suitable for use in harsh chemical environments as well as in food and beverage manufacturing. Sensors that rely on contact with the liquid, such as floats, strips, and others, become corroded and must be replaced after exposure to aggressive or harsh chemicals. Furthermore, they are unsuitable for food and beverage manufacturing, where the contact surfaces may harbor contamination, bacteria, or fungi.

 

The new PL240 level sensor from Baumer. Image used courtesy of Baumer

 

Thin Film Problems

While there are some issues with using contact sensors, they have one advantage. Floats, strips, and other systems maintain contact with the true liquid level. As long as the mechanism has been properly maintained (such as an armature for the float), the sensor should accurately report the true liquid level. With optical or capacitive contactless sensors, they can be fooled by thin films of liquid that deposit themselves on the sides of the tank. Thin films can be due to rising and falling levels of product, condensation, or dyes that discolor the inside of the tank, effectively fooling those contactless sensors.

Capacitive sensors are also easily offset by contact with other objects. For example, a technician touching the side of the tank while performing preventative maintenance on a nearby pump can cause a change in capacitance as well, causing a false level reading.

 

The PL240 Level Sensor

Thin films are not a problem for the PL240 capacitive sensor. It is capable of sensing the true liquid level by measuring a change in capacitance, rather than relying on optical transparency. This change in capacitance can be detected through opaque plastic or glass of up to 6 mm thick, regardless of the presence of thin films.

 

Mounting suggestions for the PL240 level sensor. Image used courtesy of Baumer

 

The Baumer PL240 is also not influenced by capacitive interaction with the tank. It is fine-tuned enough to filter out occasional contact from running machinery, human interaction, and other sources of capacitive spikes. The sensor allows for an air gap of up to 1 mm between the sensor and the tank, meaning it is not sensitive to the mounting mechanism; cable ties, screws, adhesive tape, and other methods are all suitable for mounting this sensor.

The PL240 series, which includes models with various wiring options for different cable connections, is powered by 10-30 volts DC, with a configurable NPN/PNP output signal and remote teaching capability.

 

Impact on Industry

The Baumer PL240 capacitive level sensor has the potential to improve process control loops with real-time, error-free level sensing. For the chemical processing industry, chemical feed rates can be more tightly controlled than with traditional optical or capacitive sensors, yet have longer sensor life than contact sensors. For the food and beverage industries, accurate levels can be measured without sacrificing product quality or safety.