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Process Control Sensors

Common sensor types found in food process control applications

Parameter Sensor Application range Special consideration
Temperature Resistance temperature detector (RTD) -430 to 1200°F 100- platinum most widely used; good accuracy—3 or 4 wire models recommended for improved accuracy.
Temperature Thermocouple
Type J
Type T
Type K

-320-1400°F
-310-750°F
-310-2500°F
Moderate accuracy—long runs of thermocouple wire not recommended due to low signal level
Volumetric flow Magnetic Down to 0.01 GPM Some minimal conductivity required; good accuracy for most control applications
Volumetric flow Vortex—shedding Down to 10 GPM High Reynolds required; can be used for steam; often used in CIP circuits
Mass flow Coriolis Down to 0.1 lb/min Highly accurate, pressure drop can be a concern; density also measured independently; good for metering applications (e.g., batching)
Mass flow Heat loss Down to 0.5 cc/min Commonly used for gasses
Level Differential pressure Down to less than 1" of water column Widely used for tank gauging; height calibration is density dependent
Level Capacitance Point level to greater than 20 ft Susceptible to product coating
Level RF impedance Point level to greater than 20 ft Reduced effects of coating
Level Ultrasonic Several inches to 100 ft Noncontact, surface perturbations can be problematic; can detect liquid/liquid interfaces

 

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