The Rosemount Model 242 Flow Through Toroidal Conductivity Sensor is specifically engineered for processes where conventional contacting sensors would corrode or become fouled. Its noninvasive flow-through design allows for in-line installations without any obstruction to sample flow, making it ideal for viscous, abrasive, or fibrous liquids containing high levels of suspended solids.

The sensor operates on the toroidal principle: two wire-wound toroids encapsulated in a non-conducting tube surround the process flow path. One toroid acts as a transmitter and the other as a receiver. Energizing the transmitter induces an electric current in the process solution, which in turn induces a current in the receiver toroid. The strength of this induced current is directly proportional to the conductivity of the solution. Metal contact rings on either side of the toroids complete the circuit by coupling the ionic current in the sample to an electronic current passing through the metal frame.

With over 250 configurations available, the Model 242 offers exceptional flexibility to meet specific application requirements. Line sizes of 1, 1.5, 2, 3, and 4 inches (25, 40, 50, 80, and 100 mm) are available with both ANSI 150/300 and DIN PN16 compatible flanges. The conductivity measurement range spans from 100 µS/cm to 2 S/cm (2,000,000 µS/cm), covering the entire range without requiring separate high or low-range sensors.

Process compatibility is ensured through a wide selection of wetted materials:

• Liners: Glass-filled PEEK (high pressure/temperature), Teflon (PTFE) (hydrofluoric acid or strong oxidizing agents), or Alumina (abrasive solutions such as alumina/caustic ratio applications)
• Contact Rings: 316 SST, Carpenter 20Cb-3 SST, or Hastelloy C-276
• O-Rings: EPDM, Viton (FKM), or Chemraz (FFKM)

The sensor is designed for easy installation. It fits between process mounting flanges without requiring special grounding rings, as contact rings are built into the sensor. Recessed bolts hold the assembly together, ensuring all internal parts remain in perfect alignment during installation. An integral Pt100 RTD temperature sensor is included and slips directly into one of the contact rings, providing temperature measurement at the exact same point as conductivity measurement without requiring a separate thermowell.

Key operational advantages include insensitivity to flow rate and direction, making it suitable for variable process conditions, and resistance to plugging since no sensor components protrude into the sample flow where solids could accumulate. The rugged construction from chemically resistant materials ensures long-term reliability in demanding environments. In-line calibration capability reduces labor and downtime.

The Model 242 is compatible with Rosemount analytical instruments including Models 54eC, 1055, 3081T, 4081T, 5081-T, and Xmt-T. Weight ranges from 22 lbs (10 kg) for 1-2" sizes to 86 lbs (39 kg) for 3-4" sizes. Typical applications include mining and metals processing, pulp and paper processing, chemical processing industry, and hydrofluoric alkylation units for polymer surge drum phase transition monitoring.