explain how the kink in the characteristics as due to secondary emission from the anode
Secondary emission Secondary emission can be undesirable such as in the tetrode thermionic valve (tube). In this instance the positively charged screen grid can accelerate the electron stream sufficiently to cause secondary emission at the anode (plate). This can give rise to excessive screen grid current. It is also partly responsible for this type of valve (tube), particularly early types with anodes not treated to reduce secondary emission, exhibiting a 'negative resistance' characteristic, which could cause the tube to become unstable. This side effect could be put to use by using some older valves (e.g., type 77 pentode) as dynatron oscillators. This effect was prevented by adding a third grid to the tetrode, called the suppressor grid, to repel the electrons back toward the plate. This tube was called the pentode.
Linear variable differential transformer When the core is displaced toward the top, the voltage in the top secondary coil increases as the voltage in the bottom decreases. The resulting output voltage increases from zero. This voltage is in phase with the primary voltage. When the core moves in the other direction, the output voltage also increases from zero, but its phase is opposite to that of the primary. The phase of the output voltage determines the direction of the displacement (up or down) and amplitude indicates the amount of displacement. A synchronous detector can determine a signed output voltage that relates to the displacement.