cable capacitance การใช้

• This cable capacitance issue limits the length and power carrying ability of AC powered cables.
• For underwater power cables, HVDC avoids the heavy currents required to charge and discharge the cable capacitance each cycle.
• A typical probe uses a 9 megohm series resistor shunted by a low-value capacitor to make an RC compensated divider with the cable capacitance and scope input.
• Hence all the stray capacitances ( the cable capacitance, the amplifier input capacitance, etc . ) are virtually grounded and they have no influence on the output signal.
• The cable capacitance of 90 pF in parallel with the scope input of 20 pF and 1 megohm ( total capacitance 110 pF ) also gives a time constant of 110 microseconds.
• However, if direct current is used, the cable capacitance is charged only when the cable is first energized or if the voltage level changes; there is no additional current required.
• It was designed to solve the problems of diminished high frequency response caused by cable capacitance, decreased signal level and high frequency response from impedance effects, and signal degradation caused by the design of circuitries in effects devices.
• Low-impedance microphones are preferred over high impedance for two reasons : one is that using a high-impedance microphone with a long cable results in high frequency signal loss due to cable capacitance, which forms a low-pass filter with the microphone output impedance.
• The resistor serves to minimize the loading that the cable capacitance would impose on the DUT . In series with the normal 1 megohm input impedance of the oscilloscope, the 9 megohm resistor creates a 10?voltage divider so such probes are normally known as either " low cap ( acitance ) " probes or " 10?" probes, often printed with the letter " X " or " x " instead of the multiplication sign, and usually spoken of as " a times-ten probe ".