Analysis & gas detection

Müller METP-Ex: ATEX Zone 1 turbidity sensor for wastewater

Müller Industrie-Elektronik reworks its METP-Ex turbidity sensor for ATEX Zone 1 applications

Measuring turbidity and suspended solids where an explosive atmosphere may occur limits the choice of optical sensors. Müller Industrie-Elektronik has redesigned and certified its METP-Ex probe for Zone 1, covering both low and high solids concentrations in wastewater and process water.

Optical measurement to ISO 7027-1

The METP-Ex is an optical sensor that determines turbidity according to ISO 7027-1. Müller states a measuring range of 0 to 100 g/l, equivalent to 0 to 300 NTU, and says the probe can be used in both flowing and standing media. It is built to work at low as well as high concentrations, which matters in wastewater plants where the solids load varies strongly between process stages.

The manufacturer lists the following applications:

  • sewage treatment plant processes
  • wastewater and sludge treatment
  • condensate monitoring
  • measurements in the process industry
  • process water monitoring

Probe in the hazardous area, transmitter outside

The sensor is approved for use in Zone 1 hazardous areas. Its LED-based probe head is connected to an intrinsically safe, ATEX-certified transmitter from Müller’s MATU platform, and both components are fully encapsulated. The transmitter is installed outside the hazardous area, with a cable of up to 100 m between probe and electronics. That arrangement keeps the configuration and signal-processing hardware out of the Ex zone while only the probe is immersed in the medium.

The output is 4-20 mA or, programmable, 0 to 10 V in 3-wire connection, with a supply of 12 to 30 V DC. The probe housing is made of stainless steel 1.4571 and rated IP68. Operating temperature is 0 to 50 °C and the maximum operating pressure is 6 bar.

Müller presents the redesign as a response to other suppliers withdrawing comparable products from the market.

“When competitors discontinue products, we improve upon them and develop them further!”

— Matthias Müller, founder, Müller Industrie-Elektronik

Key facts

  • Measuring principle: optical turbidity to ISO 7027-1
  • Range: 0-100 g/l (0-300 NTU)
  • Output: 4-20 mA or 0-10 V (programmable), 3-wire; supply 12-30 V DC
  • Approval: ATEX, Zone 1; cable to transmitter max. 100 m
  • Housing: 1.4571 stainless steel, IP68; 0-50 °C; max. 6 bar