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	100-½ 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