Soft sensor or virtual sensor is a common name for software where several measurements are processed together. There may be dozens or even hundreds of measurements. The interaction of the signals can be used for calculating new quantities that need not be measured. Soft sensors are especially useful in data fusion

Sensor fusion

Sensor fusion is the combining of sensory data or data derived from sensory data from disparate sources such that the resulting information is in some sense better than would be possible when these sources were used individually...

, where measurements of different characteristics and dynamics are combined. It can be used for fault diagnosis

Diagnosis

Diagnosis is the identification of the nature and cause of anything. Diagnosis is used in many different disciplines with variations in the use of logics, analytics, and experience to determine the cause and effect relationships...

 as well as control applications.

Well-known software algorithms that can be seen as soft sensors include e.g. Kalman filter

Kalman filter

In statistics, the Kalman filter is a mathematical method named after Rudolf E. Kálmán. Its purpose is to use measurements observed over time, containing noise and other inaccuracies, and produce values that tend to be closer to the true values of the measurements and their associated calculated...

s. More recent implementations of soft sensors use neural network

Neural network

The term neural network was traditionally used to refer to a network or circuit of biological neurons. The modern usage of the term often refers to artificial neural networks, which are composed of artificial neurons or nodes...

s or fuzzy computing

Fuzzy logic

Fuzzy logic is a form of many-valued logic; it deals with reasoning that is approximate rather than fixed and exact. In contrast with traditional logic theory, where binary sets have two-valued logic: true or false, fuzzy logic variables may have a truth value that ranges in degree between 0 and 1...

.

Examples of soft sensor applications:

• Kalman filter
  Kalman filter
  In statistics, the Kalman filter is a mathematical method named after Rudolf E. Kálmán. Its purpose is to use measurements observed over time, containing noise and other inaccuracies, and produce values that tend to be closer to the true values of the measurements and their associated calculated...
  
  s for estimating the location
  Location (geography)
  The terms location and place in geography are used to identify a point or an area on the Earth's surface or elsewhere. The term 'location' generally implies a higher degree of can certainty than "place" which often has an ambiguous boundary relying more on human/social attributes of place identity...
  
  
• Velocity estimators in electric motor
  Electric motor
  An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...
  
  s
• Estimating process data using self-organizing
  Self-organization
  Self-organization is the process where a structure or pattern appears in a system without a central authority or external element imposing it through planning...
  
   neural networks
• Fuzzy computing in process control
  Process control
  Process control is a statistics and engineering discipline that deals with architectures, mechanisms and algorithms for maintaining the output of a specific process within a desired range...
  
  
• Textile sensors, often multifunctional, used in sensory data capture garments and produced by SmartlifeInc SmartLife

External links

• Helsinki University of Technology
• Soft Sensors for process applications in gas industry