Conductance (Boylestad)

• electric field is represented by electric flux line, which are drown to indicate the strength of the electric field at any point of the charged body
• denser the flux lines, stronger the magnetic field
• flux line radiate outward for positive and inward for negative
• the larger the charge, the greater the number of flux lines extending or terminating per unit area, independent of the surrounding medium
• fringing that occurs at the edges as the flux lines originating from the points farthest away from the negative plate strive to complete the connection
• permittivity is applied as a measure of how easily a material permits the establishments of an electric field in the material
• the voltage required per unit length is an indication of its dielectric strength and is called breakdown voltage
• breakdown voltage limits for how much electrical pressure in a material can handle before it stops working as an indicator and starts letting electricity through
• when breakdown occurs, the capacitors hac characteristics very similar to those conductor
• maximum working voltage 


  defines the maximum voltage that can be placed across the capacitor on a continuous basis without damaging it or changing its characteristics
• there are numbers of ways to increase the area without making the capacitor too large

  1. rolling
  2. stacking
  3. insertion
• The flux lines tend to establish a buffer action between the two with a repulsive action that grows as the two charges are brought closer to one another
• If the parallel plates are initially uncharged and the switch is left open, no net positive or negative charge exists on either plate
• it is important to note that the entire flow of charge is through the battery and resistor—not through the region between the plates. In every sense of the definition, there is an open circuit between the plates of the capacitor.
• his element, constructed simply of two conducting surfaces separated by the air gap, is called a capacitor.
• Capacitance is a measure of a capacitor’s ability to store charge on its plates—in other words, its storage capacity
• the higher the capacitance of a capacitor, the greater is the amount of charge stored on the plates for the same applied voltage.
• Michael Faraday


  he discovered electromagnetic induction, demonstrating that electrical effects can be generated from a magnetic field (the birth of the generator as we know it today). He also discovered self-induced currents and introduced the concept of lines and fields of magnetic force
• Note the fringing that occurs at the edges as the flux lines originating from the points farthest away from the negative plate strive to complete the connection
• The term permittivity is applied as a measure of how easily a material “permits” the establishment of an electric field in the material.
• relative permittivity (or dielectric constant)
• The voltage required per unit length is an indication of its dielectric strength and is called the breakdown voltage
• The charging phase — the phase during which charge is deposited on the plates
• This period of time during which charge is being deposited on the plates is called the transient period—a period of time where the voltage or current changes from one steady-state level to another
• the voltage across a capacitor in a dc network is essentially equal to the applied voltage after five time constants of the charging phase have passed
• the transient or charging phase of a capacitor has essentially ended after five time constants.
• the current of a capacitive dc network is essentially zero amperes after five time constants of the charging phase have passed
• during the charging phase, the major change in voltage and current occurs during the first time constant.
• A capacitor can be replaced by an open-circuit equivalent once the charging phase in a dc network has passed.
• The voltage across a capacitor cannot change instantaneously
• The voltage across the capacitor at this instant is called the initial value,
• This region of relatively fixed value that follows the transient response is called the steady-state region, and the resulting value is called the steady-state or final value.
• There are two general approaches to providing this linkage: capacitance sensing and conductance sensing.
• Capacitance sensing


  depends on the charge carried by the human body
• conductance sensing


  only requires that pressure be applied to a particular position on the pad.
• There are two methods commonly employed for capacitance testing.

  One is referred to as the matrix approach, and the other is called the capacitive shunt approach.
• matrix approach


  requires two sets of parallel conductors separated by a dielectric and perpendicular to each other
• That change in capacitance can then be translated by a capacitance to digital converter (CDC) and used to define the location on the screen
• capacitive shunt approach


  a sensor is used to detect changes in capacitive levels.
• The term shunt comes from the fact that some of the electric field is “shunted” away from the sensor.