Thursday, September 16, 2010

Sensor Research

From Sensor Wiki:

Temperature-transducer ICs

Semiconductor temperature sensors are produced in the form of ICs. Their design results from the fact that semiconductor diodes have temperature-sensitive voltage vs. current characteristics. When two identical transistors are operated at a constant ratio of collector current densities, the difference in base-emitter voltages is directly proportional to the absolute temperature.
The use of IC temperature sensors is limited to applications where the temperature is within a –55° to 150°C range. The measurement range of IC temperature sensors may be small compared to that of thermocouples and RTDs, but they have several advantages: they are small, accurate, and inexpensive.
Temperature sensing ICs are available either in analog form, which output a voltage or current which is proportional to the temperature, or digital, which communicate temperature over a digital communication line, such as one-wire PWM, two-wire I2C, or a multiple wire SPI connection.

Piezoelectric Sensors

Piezo sensors are used to convert mechanical movements, such as force, vibration, acceleration or pressure, into electric signals. Piezoelectric elements are widely used in a variety of sensors such as accelerometers, contact mics, and ultrasound transducers. Piezoelectric sensors can be used as force-sensitive switches, threshold detectors, analog pressure sensors, and acoustic vibration pickup.

Piezoelectric ceramic elements are also found in watches, alarm clocks, old portable video games, and many other commercial products which contain sound generating devices. Piezo-buzzers typically operate at their resonant frequency with various construction options. Since in many cases piezo sensors are simply reversed buzzers and actuators, these sensors exhibit a resonant frequency that they are more sensitive to. These inexpensive transducers can be salvaged from old products or obtained from the usual sources (i.e. digikey, etc.) with specific electrical properties (operating voltage range, sensitivity, capacitance, resonant frequency, etc.) for optimal operation.

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