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Showing posts from July 18, 2010

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The History of the Telephone - Alexander Graham Bell

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Alexander Graham Bell and Elisha Gray raced to invent the telephone.
In the 1870s, two inventors Elisha Gray and Alexander Graham Bell both independently designed devices that could transmit speech electrically (the telephone). Both men rushed their respective designs to the patent office within hours of each other, Alexander Graham Bell patented his telephone first. Elisha Gray and Alexander Graham Bell entered into a famous legal battle over the invention of the telephone, which Bell won.
The telegraph and telephone are both wire-based electrical systems, and Alexander Graham Bell's success with the telephone came as a direct result of his attempts to improve the telegraph.
When Bell began experimenting with electrical signals, the telegraph had been an established means of communication for some 30 years. Although a highly successful system, the telegraph, with its dot-and-dash Morse code, was basically limited to receiving and sending one message at a time. Bell's extensive k…

The insides of a modern pressure transducer

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Further on in our voyage, we come to small circuit board. The two voltage out points from the bridge circuit are fed to an amplifier that changes the very small voltage into a 0-5V signal or most commonly to a 4-20 mA signal. This signal is fed out the cable (sometimes along with a vent tube) which finishes our voyage.
The output of a Strain gauge is sometimes referred to as ratiometric to the supply voltage. The term ratiometric means that the output varies as a ratio of the the supply voltage. An example helps make all things things clear.
· Let us assume that With a 1/2 full scale pressure input the out put is x volts, if we double the supply voltage, the voltage output will now be 2X.
By varying the supply voltage we have a handy way to scale the output to what ever units we want. Changing the value of the reference element resistor gives us a way to offset the zero point. Between the two adjustments we can scale and offset the output to what ever we want. In real word practice the ou…

Pressure Transducer Basic

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Pressure transducers used in industry today take on a rather typical appearance. A round, tubular stainless steel body with a pipe fitting on one end and a cable coming out of the other end. Stainless is used because of its high strength and resistance to corrosion.
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