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January 28, 2006
Basics of Sensors 01.17.06
What is a sensor?
Converting one form of energy into another.
How can we exchange energy forms?
• RFIDs (Radio Freq Identification) embedded into pets to locate and track them.
• Inductance: When current is passed through a wire, it generates a magnetic field. Ex. Motors, radios etc
• Passive RFIDs : Reading the bounced back energy; the difference in signals.
• RS232 : Serial Protocol
Class Requirements
Sensor Report: individual
• What the sensor does
• The interface
• How to use it
• Schematics and codes
In-class sensor reports
Reading and questions of the datasheets
When looking at different sensors, we look at
• Its stability
• What energy it reads
• States in analog, the sensitivity (threshold) and the range of voltage that we get
Threshold: The point at which a signal (voltage, current, etc.) is perceived as valid.
• Dynamic range input and the output range
• Resolution in different applications, what resolution does our application need?
• Temporal resolution (the time that affects the sensor), depending on the response time. Ex light switches, when they don’t react in time, we may end up switching it a few times. HMI lights ((Hydrargyrum Medium arc Iodide) A flicker-free light source recommended for digital cameras that require long periods of exposure) take a while to turn on. In this case, the output is taking long.
• Bandwidth of sensor : how fast it can read.
• Transfer: how does input become an output? Linear growth. y=mx+b
Non-linear growth: usually the end points, the data that we can not work with.
• Hystereses in sensors : contained in one zone that shows a range of possible relationships in the readings. Variability within a range (bouncing on and off)
• Debouncing in switches: allows the values to settle.
• Noise: values that you don’t want in the readings. High signal to noise are reliable sensors. Which means that the hardware itself filters out and averages.
Negative feedback (to the direction going): reverses the data received.
Positive feedback: amplifies the data received. Ex in EEG system
When tiny voltages are involved, we amplify the signal to a particular point to get better readings. This may cause the signal to increase faster when it is rising
Reading sensors
Digital Oscilloscope: To read sensors over a long period of time. Reading the electrical signal change. One can look at the signals very closely
Channel 1, VOL TS-DVV to amplify visual and to read finer resolutions.
SEC/DEV
Posted by min at January 28, 2006 03:37 PM