Due to the lack of moving parts, the design of the Signet Magmeter allows for several advantages over paddlewheel sensors, one of which is reliable performance in liquids containing solid particles. So far to date, customers have reported successful performance in liquids containing solids of up to 25%, including a PCB manufacturer whose waste water contained fiberglass strands and broken PCB boards. In these types of “dirty” applications, a general rule of thumb is to limit the particles to a size and type that will not damage the sensor tip (i.e. no abrasion). Solids should NOT be oily in nature (sewage, food, oils, grease) as any non-conductive substance that coats the sensor tip will cause an erratic flow rate reading. Should the electrodes become coated, we recommend the sensor be cleaned with soap and water to maintain a satisfactory level of operation.

The minimum conductivity value, as stated in the product specifications, is 20 μS and customers have asked if the Magmeter will continue to work below this point. However, due to slight variances between sensors, we do not specify a safety margin. During verification tests, the Magmeters have performed down to 12 μS with some degree of reliability, but without 100% pass rate for all sensors; the 20 μS minimum point is guaranteed. Below this point, flow velocities should be less than 3 m/s (10 ft/s). Similarly at the upper conductivity measurements, our verification tests were successfully conducted with various chemicals (shown below) to a maximum of 350,000 μS. Liquids with higher values may be suitable but are typically very aggressive and may shorten the service life of the sensor. Use the appropriate chemical compatibility guides to determine the sensor materials suitable for your application.

  •   5% sodium hydroxide: 250,000 μS
  •  10% sodium hydroxide: 350,000 μS
  •  0.5% hydrochloric acid: 50,000 μS
  •  1% hydrochloric acid: 130,000 μS
  •  1% sulfuric acid: 40,000 μS
  •  5% sulfuric acid: 250,000 μS

The Signet 2551 Magmeter has proved successful in many applications with challenging process conditions. Should you find similar success, we would like to hear from you; we will add your success story to a future Tech-Tip and give you full recognition for your submission. Also, if you require any further assistance, please contact the Georg Fischer Signet Factory at signet.ps@georgfischer.com.