General info and working of smart sensors covers about ASPU, Convertors, Microcontrollers and Compensation techniques

1. SMART SENSORS
(INTELLIGENT SENSORS)
 Sensors
 Analog Signal Processing Unit
 Converter Unit
 Micro controllers

2. A sensor with interfacing circuits capable of performing
the following functions is said to be a smart sensors
Automatic ranging
Automatic calibration
Automatic decision making

3. Typical Intelligent sensor and actuator

4. • The properties of an intelligent field devices are:
Automatic ranging and calibration through a built in difital
system
Auto acquisition and storage of calibration constants in the
local memory of filed devices
Auto configuration and verification of hardware
Auto correction of offsets, time and temperature drifts
Auto linearization of non linear characteristics
Communication through a serial bus

5. • The motive behind development of smart sensors is:
Compensation for the non ideal behavior of sensors
Provision of communication of process data with the host
system.
Signal conditioning based on the output of the sensor
• Smart sensors provide new sensing methods improved
computing capability and digital communications.

6. A sensor interfaced with a host system

7. SENSOR:
• The sensor provides an electric output in
response to the physical quantity it receives
as input .
• The advanced sensor technology are
Semiconductor sensors, micro machined
semiconductors and IC sensors.

8. Analog Signal Processing Unit
• The ASPU is the analog signal processing unit that
consist of the power supply, amplifiers and filters.
• The power supply generally refers to the power supply to
the sensor
• The power source can either be a D.C. source or a A.C.
source as per the application demands.

9. • Amplifier is another component found in almost all sensor
system.
• Filters are used to remove unwanted noise signals
caused when gain requirement is high.
• Analog filters are commonly used because digital filters
consumes more power.

10. Convertor Unit
• The convertor unit can either be a D.C. source or A.C.
source as the application demands.
• Data conversion from analog amplitude to frequency is
often done for convenient signal transmission internally or
externally and for subsequent digital conversion.
• Voltage-frequency conversion is carried out using
multivibrators.

11. Microprocessor
• The micro controller is used to overcome the following
defects in a sensor:
• Non linearity
• Noise
• Response time
• Drift
• Cross sensitivity
• Interference
• Sometimes the sensor responds to additional variables
apart from the measured variables.

12. • Some compensation techniques are followed to maintain
the sensitivity:
• Monitored compensation
• Structural compensation
• Tailored compensation
• Deductive compensation

13. • MONITORED COMPENSATION:
The compensation is done by devising an
algorithm that monitors the change in response
characteristics because of the interfering quantity.
• STRUCTURAL COMPENSATION:
Care is taken while designing the sensor such that
desired o/p is derived through differential mode and
interfering signals are derived through common mode are
rejected.

14. • TAILORED COMPENSATION:
Compensation is done individually on each sensor
depending on its performance and response to inputs. Here
a dedicated algorithm has to be developed or specialized
analog module has to be incorporated.
• DEDUCTIVE COMPENSATION:
When the variables are not physically accessible,
model reference data sets are considered and
compensation technique is called deductive compensation.