Multivibrator for static relays having linear time dial

Claim 1

A static relay comprising: a current-sensing circuit; a charging network connected to said current-sensing circuit said charging network having input terminals connected to said current-sensing circuit, and output terminals; the voltage at said output terminals increasing with time according to a predetermined curve after said current-sensing circuit is connected to said input terminals of said charging network; pickup circuit means connected between said current-sensing circuit and said input terminals of said charging network; said pickup circuit means energizing said input terminals of said charging network when the output of said current-sensing means exceeds a predetermined value; output circuit means connected to said output terminals of said charging network and being energized when the output of said output terminals exceeds a predetermined value; and continuously operating switching circuit means comprising a multivibrator means having first and second transistors each having first, second and control electrodes; first capacitor means (Co) coupled between the control electrode of said first transistor and the first electrode of said second transistor; second capacitor means (C1) coupled between the control electrode of said second transistor and the first electrode of said first transistor; first and second resistance elements each having a first terminal connected respectively to the first electrodes of said first and second transistors and a second terminal coupled to said current sensing circuit; a third resistance element (Ro) coupled between the control electrode of said second transistor and said current sensing circuit; fourth and fifth resistance means being connected in series between the control electrode of said first transistor and said current sensing circuit; said resistance means comprising a variable resistance element having an adjustable member; dial means including an adjustable knob means and face plate having uniformly spaced graduations cooperating with a pointer on said knob means for adjustably setting the desired time setting of said multivibrator; said knob means being connected to said adjustable member to vary the resistance of said fourth resistance means; the uniform graduations being obtained by the proportional relationship between said fourth resistance means (R1) and said third resistance means given by the equation: R1 (RoCo/C1) (a - 1) -R2 where a (T1+ To/To) and To is the time interval during which said second transistor is non-conductive and T1 is the time interval during Which said second transistor is conductive.