Control system for a chromatography apparatus oven door

In a chromatography apparatus of the type including an oven for a chromatography column of said apparatus, and electric heater means for controllably heating said oven, an improved system for controllably opening and closing the door of said oven to enable a controlled heat flow to thereby stabilize the temperature of said oven at a desired set point, said system comprising:

• heat sensor means at said oven for generating a signal indicative of the temperature in said oven;
• first comparator means for comparing said oven temperature indicative signal with said set point temperature and generating an output signal at first or second relative polarities indicative, respectively, of departure of the temperature of said oven in a positive or negative direction from said set point;
• heater power control means for receiving the output signal from said first comparator means, said heater power control means being enabled when said first comparator means output signal is at said first relative polarity to effect heating of said oven and being inactive when said first comparator means output signal is at said second relative polarity;
• bi-directional motor means for opening and closing said oven door over a prescribed operating range;
• first and second reference level signal generators for providing first and second threshold signals, respectively;
• door open comparator means and door close comparator means for receiving the threshold signals from said first and second reference level generators and for receiving the output signal from said first comparator means, said door open comparator means providing an output signal when said first comparator means output signal is above said first threshold signal, and said door close comparator means providing an output signal when said first comparator means output signal is below said second threshold signal;
• door open power control means and door close power control means connected to actuate said bi-directional motor means in the directions effective to open and close said oven door;
• the output signals from said door open and said door close comparator means serving to enable said door open and said door close power control means, respectively, through time delay means, whereby an enabling output signal from said door open comparator means or from said door close comparator means is provided to said door open power control means or to said door close power control means only when said enabling signal extends for the duration of the delay provided by said time delay means;
• and
• timer means associated with said door open and said door close power control means for limiting the period of operation of said door open and said door close power control means to thereby enable incremental stepwise movement of said oven door.