Sensors and Transducers Flashcards
what is a sensor ?
It is device that provides an electrical signal related to physical quantity being measured
What is a transducer ?
often used instead of ‘sensor’, elements used to convert signals from one form to another
What are sensors/tranducers ANALOGUE
IF and only if the output is ANALOGUE. An Analogue output changes in a continuous way and its size is proportional to the size of the variable being measured.
What are sensors/transducers DIGITAL
IF and only if the output is of a DIGITAL nature.
What are smart sensors?
Sensors combined with signal conditioning and microprocessor.
What is the Microprocessor ?
It is the brain of mechatronic system. It processes the data and performs all the arithmetic. It is the ARITHMETIC LOGIC UNIT of the mechatronic system. The microprocessor is often called the CPU.
What is a microcontroller ?
Single chip with including a Microprocessor, memory and peripherals.
Range of span of transducers
RANGE: Defines the limit between which, input can VARY
SPAN: MAX INPUT-MIN INPUT
Accuracy of transducers
extent t which the value measured might be wrong (summation of errors, incl calibration error).
Hysteris error of transducers
Transducers can give different output from same value of quantity being measured. MAX difference in output for increasing and decreasing value of input.
Error of transducers
Measured value - true value
Sensitivity of transducers
How much output there is per unit input (O/I) output variation/input variation
Non linearity error of transducers
Error defined as max difference from straight line
Repeatability/reproducibility of transducers
Ability to repeat/reproduce same output of the same input value. Percentage of full range output.
error resulting from same output not being given with repeated application
Repeatability = (Max-Min values/ full range)x100
Stability of transducers
ability to give same output for measuring a constant input over time. Drift is used to express change in output (zero drift: change when there is zero input)
Resolution of transducers
Input varies over the range, output signals for some sensors may change in small change (smallest value of I variation observable from output)
ex: Resistance temperature detectors (RTDs)
resistance of most metals increases over a limited Tr, in a reasonably linear way with temperature.
ex: Thermistors
Resistance of semiconductors (oxides that thermistors are made from) decreases in a very nonlinear manner with an increase in temperature.
Such thermistors have negative temperature coefficient (NTCs)
ex: Thermocouple
Two strips of metal joined together, p.d occurs across the junction. The p.d depends on metal used and temperature of the junction. By measuring voltage across junction, can measure temperature
ex: (light) different types of photodiodes
Highly non linear, integrated light-to-voltage sensors. Requires A/D conversion to be integrated. Light->sensor->voltage
Actuators
devices providing physical quantity related to electrical output of control system.
Actuators-main specs and types
No standard specs, depends on type of automation
TYPES of automation:
Pneumatic actuators
Mechanical actuators
Electrical actuators (electrical DC motor)
