Capacitive level switch for fluid, pasty and powdery media

A capacitive level switch used mainly for the registration of limit levels, full/empty signals in pipes and tanks in fluid, pasty and powdery media and for the dry running protection of pumps, has been introduced.

Martens, part of the GHM Group of companies, introduced the MLC 437 capacitive level switch which is designed for applications in sectors requiring hygienic areas and the chemical industry. The company states that the parts of the switch which come into contact with the media consist only of materials which conform to FDA regulations. With the aid of the microprocessor-controlled measurement, the user is able to adapt the parameter setting to the process environment using computer technology.

GHM Messtechnik SA explains that the MLC 437 capacitive level switch has an analogue output and a DK-value (dielectric constant) which will enable applications requiring the measurement of differences between oil and water levels - a crucial element to maintaining consistency in the manufacture of products such as chemicals, pharmaceuticals and cosmetics, including applications where hygienic areas are essential.

The company further affirms that a unique feature of the MLC437 is that during operation, if an error or condition occurs, the display backlight can be set to change color. This is to give engineers an easily identifiable alert to the condition so that the error can be addressed.

During measuring operations, the liquid crystal display shows measured values. The parameters can be set to allow the backlight to permanently operate or for the device to enter into a power safe mode.

The switches register fluid, granular and pulverised media but are not applicable for use in areas subject to the risk of explosion. The charge transfer measurement procedure makes use of the storage capability of charges in the medium. The switch tip and the tank wall, or built-in adapter/sleeve, thus forms an electrical condenser.

If the switch is in the air, a specific low initial capacity is measured. When the switch is immersed in the medium, the capacity change is based on a change in the effective permittivity in the area of the measuring tip. This value is determined by the geometry of the switch and the DK-value of the medium. The measurement procedure enables the monitoring of the product and the detection of any separating layer, such as water or oil. Influences due to foam formation and adhesions are said to be negligible.

The technical features of the MLC437 are:

• Power supply:
  • Supply voltage: 18-30 V DC, max. 100 mA
  • Electrical connection: M12x1 plug
  • CE-conformity: EN 61326:2007-05
  • Ambient conditions
  • Ambient temperature: -20 °C to 60 °C
  • Climatic class: EN 60068-2-38:2010-06
  • Vibration class: EN 60068-2-6, GL test2
• Certifications
  • EHEDG Certificate No. 28/2011
• Sensor
  • Radiated frequency: 40.68 MHz, <1 mW
  • Measuring range: DK-value 1.5 – 17
  • Initialization time: 3 seconds
  • Process temperature: -20 °C to 100 °C, 140 °C < 30 min
  • CIP-/SIP-capable
  • Process pressure: -1 to +10 bar
  • Process material: PEEK, FDA approval number 21CFR177.2415 - food-safe according to EHEDG and conforms to Regulation EC 1935/2004 and 10/2011

The company asserts that its capacitive level switch is also easy to service and maintain.