Electromagnetic transmission

Even if the receptor by itself has high accuracy, the sensor may be unable to execute the measurement in a defined place. Quality and total accuracy depend on the combination of receptor, the converter for measured values, and mechanical protection. Mechanical protection can take the form of pockets in water and fluid and also assembly boxes which protect against pollution, humidity, and temperature in the surroundings or against electromagnetic transmissions and noise from power-supplied pipes and cables. 

Amplitude Modulation (AM). With AM radio, the amphtude (height) of the transmitted signal is made proportional to the sound amplitude captured (transduced) by the microphone. The transmitted frequency remains constant. AM transmission is degraded by static and interference because sources of electromagnetic transmission such as lightning and automobile ignitions, which are at the same frequency, add their amplitudes to that of the transmitted signal. AM radio stations in the United States and Canada are limited to 50 kilowatts (kW). Early twentieth century, U.S. stations had powers up to 500 kW, some of which could be heard worldwide. 

Electrical sources static electricity, electrical current, lightning, stray currents (radiofrequency electromagnetic radiation, overhead high voltage transmission lines, galvanic and cathodic protection stray currents)... 

Tesla now devoted his energies to work in his own laboratory in New York City, llis inventions were numerous. He experimented with the transmission of signals using electromagnetic waves at the same... 

Transformers are electromagnetic devices that allow electrical power supplied at one potential to be transformed into electrical power at another potential. The potential or voltage may be stepped up (increased) or stepped down (decreased). For instance, in the usual transmission of domestic power, the potential in the transmission lines is greater than the load requirements and a step down transformer is used to reduce the potential at the end use point. 

Two methods are currently used to transmit data from downhole to surface mud pressure telemetry and electromagnetic earth transmission. 

Figure 4-253. Principle of the electromagnetic MWD transmission. (Courtesy Geoservices [109]. ...

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