Controller for variable air volume cooling system

In a variable air volume cooling system,

• fan means for blowing air into an area to be cooled,
• means for varying the amount of air blown into said area including a driver variable pitch pulley means, a driven variable pitch pulley means, and a belt means connected between said driver and driven pulley means, whereby changes in the pitch of said driver pulley means varies the diameter of the belt on said driver to effect changes in the speed of said fan means, driving motor means connected to said driver pulley means, servo-motor means mounted to drive a means for effecting changes in the pitch of the driver pulley means;
• a first electrical signal derived from a temperature sensing means in said area to be cooled, pulse generating means connected to said fan means producing second signals indicative of the speed thereof, means for comparing said first and second signals to produce a control signal which is connected to said servo-motor means to effect a change in said diameter, said means for comparing including:
• means for shaping said signal to be the actual temperature condition signal applied to the inverting input of a difference amplifier means;
• means for converting the pulses of said second signal into an analog reference signal connected to the non-inverting input of said difference amplifier means;
• means for adjusting the minimum speed of the fan means, means for adjusting the maximum speed of the fan means, said two adjusting means connected to said means for shaping said first signal;
• a first and a second comparator difference amplifiers are connected to the output of said difference amplifier whereby said first comparator produces output when the output of said difference amplifier is positive, and said second comparator produces outputs when the output of said difference amplifier is negative, the output of said first comparator is connected to a first solid state switch, the output of said second comparator is connected to a second solid state switch;
• said time delay means is connected to each of said solid state switches to effect the control deactivation until the fan reaches operating speed, the outputs of said solid state switches are connected to a first and a second current isolating driver means and to first and second triacs;
• the output of said first solid state switch is connected to said first current isolating driver means to which is connected said first triac, the output of said second solid state switch is connected to said second current isolating driver means to which connected said second triac;
• servo-motor power means connected to said triacs and said servo-motor so that driving signals on said first triac produce clockwise operation of said servo-motor and driving signals on said second triac produce counter-clockwise operation of said servo-motor.