Defrost control system

Apparatus for controlling defrost means in at least one refrigeration unit, comprising:

• means for effecting actuation of the defrost means at a defrost time and including a programmable timer for selectively scheduling the defrost initiate time;
• the timer including a microprocessor responsive to the frequency of a clock signal for controlling the defrost timing by the timer;
• means responsive to a determined absolute humidity parameter for controlling the defrost initiate time, and including means for providing said clock signal to said timer and for effecting a variation in the frequency of the clock signal with a variation in the determined absolute humidity;
• and
• the clock signal means providing a clock signal having a first fixed frequency corresponding to a first predetermined temperature and/or relative humidity levels, and having a second fixed frequency corresponding to a second predetermined temperature and/or relative humidity levels, and having a third frequency spectrum corresponding to a predetermined range of absolute humidity conditions.

Apparatus for controlling defrost initiation of a refrigeration unit having refrigeration and defrost means, comprising:

• temperature sensor means for providing a first signal indicative of the temperature ambient to said unit;
• relative humidity sensor means for providing a second signal indicative of the relative humidity ambient to said unit;
• first analog-to-digital circuit means for digitizing said first signal;
• second analog-to-digital circuit means for digitizing said second signal;
• third circuit means responsive to the digitized first signal to provide a third signal substantially indicative of the saturation humidity of a unit of air at the temperature represented by the digitized first signal;
• signal generating means responsive to the digitized second signal to provide a fourth signal having a frequency which varies as a function of the relative humidity;
• fourth circuit means responsive to said third and fourth signals for providing a fifth signal having a frequency which varies as a function of the third and fourth signals;
• and
• timer means providing a defrost initiate signal to effect defrost initiation of the refrigeration unit at periodic intervals, said timer means varying said periodic intervals as a function of the frequency of said fifth signal.

Apparatus for controlling defrost means in at least one refrigeration unit, comprising:

• means for effecting actuation of the defrost means at a defrost time and including a programmable timer for selectively scheduling the defrost initiate time;
• the timer including a microprocessor responsive to the frequency of a clock signal for controlling the defrost timing by the timer;
• means responsive to a determined absolute humidity parameter for controlling the defrost initiate time, and including means for providing said clock signal to said timer and for effecting a variation in the frequency of the clock signal with a variation in the determined absolute humidity;
• and
• the means responsive to the absolute humidity including a temperature sensor for measuring an ambient temperature and for providing a first signal indicative of the measured temperature, and having a relative humidity sensor for measuring a relative humidity condition and for providing a second signal indicative of the measured relative humidity, and having a signal processing means responsive to said first and second signals for deriving a third signal having a frequency which varies in proportion with change in the absolute humidity.