Proportional electric heat control system

Claim 2

A proportional heat control circuit for controlling an output to a load in response to a plurality of input temperature conditions comprising: a first and second temperature sensing means for developing a first and a second voltage signal representative of a first and second temperature condition respectively; means associated with each of said first and second sensing means for establishing a signal representative of an ambient temperature condition around which said first and second sensing means operate and wherein said means each generate a constant voltage signal representative of said ambient temperature condition; ratio control means for adjusting the relative proportional effect that said second temperature sensing means will contribute to said output load in relation to said first temperature sensing means, wherein said control means comprises a variable resistor connected in series with said second temperature sensing means; means for developing an error voltage signal from said signals of said first and second temperature sensing means, from said ambient temperature condition means and from said ratio control means coMprising an operational amplifier; means for changing the sensitivity of said operational amplifier comprising a resistive feedback path around said operational amplifier; means for generating a sawtooth reference voltage signal; means for comparing said sawtooth reference voltage signal with said error voltage signal wherein an output signal is obtained only when the magnitude of said error voltage signal is less than the magnitude of said reference voltage signal; pulse generator means connected to said comparing means wherein a voltage pulse is generated only when said output signal is applied to said pulse generator means; and a zero voltage switching means connected to said pulse generator means wherein a signal is provided to said load only when said pulse generator is generating a pulse.

Claim 3

A proportional heat control circuit as defined in claim 1 wherein said zero voltage switching means comprises an AC source; a first and second SCR connected to said AC source, and SCR''s being connected in back-to-back relationship; said load connected to said SCR''s; a first means to render said first SCR conductive at a first zero crossover point of said AC source comprising a first and second switch means, a first capacitor and a first breakdown diode; a second means to render said second SCR conductive at a second alternative zero crossover point of said AC source comprising a third switch means and a second capacitor; a third means connected to said pulse generator means and to said first means for supplying a train of pulses to render said first and second switches conductive only when said pulses are present and wherein said first SCR becomes conductive when said AC source changes from positive to negative; and said first SCR being connected to said second means to render said third switch means conductive and wherein said second SCR becomes conductive only when said AC source changes from negative to positive and said first SCR is conductive.

Claim 4

The zero switching circuit of claim 2 wherein said first and third switch means are four layer diodes,

Claim 5

The zero switching circuit of claim 3 wherein said second switch means is a transistor,

Claim 6

The zero switching circuit of claim 4 wherein said third means is a pulse transformer. 6 The zero switching circuit of claim 5 wherein the pulses applied to said pulse transformer are developed from a proportional control circuit.

Claim 7

A proportional control circuit for controlling an output load in response to a plurality of input conditions comprising: a first sensing means for developing a first variable DC voltage signal in response to a first sensed condition, said first variable DC voltage signal having a predetermined polarity and an amplitude which varies proportionately with variations in said first sensed condition; a first setpoint control means for summing with said first variable DC voltage signal an adjustable DC setpoint potential of polarity opposite to said first variable DC voltage signal; a second sensing means for developing a second variable DC voltage signal in response to a second sensed condition, said second variable DC voltage signal having the same polarity as the first variable DC voltage signal and an amplitude which varies proportionately with variations in said second sensed condition; a second setpoint control means for summing with said second variable DC voltage signal a second adjustable DC setpoint potential of polarity opposite to said second variable DC voltage signal; ratio control means connected to said second sensing means and said second setpoint control means for adjusting the relative proportional effect of said second sensing means on control of said output load in relation to said first sensing means by adjustment of the sum of the second variable DC voltage signal and said second DC setpoint potential in linear proportion Relative to the sum of said first variable D.C. voltage signal and said first DC setpoint potential; means for summing the output of said ratio control means with the sum of said first variable DC voltage signal and said first DC setpoint potential to provide a composite DC condition error signal; means for amplifying said composite condition error signal; an adjustable resistive feedback path around said amplifying means for adjustment of the gain of said amplifying means for sensitivity control; and means responsive to the output of said amplifying means to provide an output load control signal.

Claim 8

A proportional control circuit for controlling an output load in response to a plurality of input conditions comprising: a first sensing means for developing a first variable DC voltage signal in response to a first sensed condition, said first variable DC voltage signal having a predetermined polarity and an amplitude which varies proportionately with variations in said first sensed condition; a first setpoint control means for summing with said first variable DC voltage signal an adjustable DC setpoint potential of polarity opposite to said first variable DC voltage signal; a second sensing means for developing a second variable DC voltage signal in response to a second sensed condition, said second variable DC voltage signal having the same polarity as the first variable DC voltage signal and an amplitude which varies proportionately with variations in said second sensed condition; a second setpoint control means for summing with said second variable DC voltage signal a second adjustable DC setpoint potential of polarity opposite to said second variable DC voltage signal; ratio control means connected to said second sensing means and said second setpoint control means for adjusting the relative proportional effect of said second sensing means on control of said output load in relation to said first sensing means by adjustment of the sum of the second variable DC voltage signal and said second DC setpoint potential in linear proportion Relative to the sum of said first variable D.C. voltage signal and said first DC setpoint potential; means for summing the output of said ratio control means with the sum of said first variable DC voltage signal and said first DC setpoint potential to provide a composite DC condition error signal; means for amplifying said composite condition error signal; an adjustable resistive feedback path around said amplifying means for adjustment of the gain of said amplifying means for sensitivity control; and means responsive to the output of said amplifying means to provide an output load control signal.