Texas Instruments Corporation

Other

Mitchell R Rowlette

Mark Eric Miller

Ronald E Garnett

Youn H Ting

Walter H Bailey

Mark A Eifler

Craig M Nold

Kenneth L Hayden

Gary J Steffes

Robert B Brown

Tim H McMains

Francois A Padovani

Werner Strasser

Robert K Chaney, Jr

Darryel L Price

Alan R Sawyers

A control used in a two stage HVAC system has a power supply from a 24 VAC transformer which is full wave rectified (D D D D ) to create DC voltages for a microcontroller (U ) and relays (K -K ). All of the control information needed for the two stage control system is sent to the control from a room thermostat ( ) having first and second stage cooling signal terminals (Y , Y ) over a single line by connecting a diode between the Y , Y terminals creating separate microprocessor recognizable signals.

Method and apparatus for wiring room thermostat to two stage HVAC system

A gas furnace control for two stage gas furnaces which can be used with either a single stage or a two stage room thermostat monitors the length of time the first, low combustion, stage is energized and upon exceeding a selected period of time, e.g., 10 minutes, energizes the second, high combustion stage. Energization of the second stage signal (W,) also energizes the second stage without regard to timing of the first stage.

Universal two stage gas furnace ignition control apparatus and method

A microprocessor based control for monitoring oil pressure of compressors can use a normally open or a normally closed pressure switch (S,S,) and LED indicator (LED,) having a diode isolated power supply (VDD,SENSOR) separate from the power supply (VDD) of the microprocessor (U,). Timing of the microprocessor is derived from the frequency of the line (60 Hz). The microprocessor is normally in a sleep mode and is awakened by each 60 Hz interrupt to check the condition of the pressure switch, the accumulated time that inadequate pressure has occurred and whether the relay needs to be energized and then returns to the sleep mode. The resulting reduced power requirement enables extended retention of accumulated &ldquo;bad&rdquo; oil time. Since oil pressure does not build-up to a satisfactory level for the first eight seconds or so upon start-up, the microprocessor senses whether the oil pressure indicates good oil immediately upon start-up which indicates a fault condition and if so will shut the system down but only after approximately four seconds which allows the compressor to be jogged, or momentarily energized, to force refrigerant out of the compressor and into the system, which is necessary on initial start-up of the compressor system.

Differential oil pressure control apparatus and method

An integrated heat pump and electrical heat control (,) has thermostat signal inputs (O, W,, W,, G, Y) along with a defrost sensor input (DF_IN). The defrost sensor (,) is located in an outdoor unit (,) which also includes a compressor contactor (CC), condenser fan (,) and reversing valve (,) relays (K,, K,, K,) controlled by micro-controller (U,). The normally closed condenser fan relay (K,) is energized through the defrost sensor forming a hardware lock-out in which the defrost sensor contacts must be closed for relay (K,) to be actuated de-energizing the condenser fan. The compressor contactor (CC) is energized through a low pressure switch (,) and high pressure switch (,) forming another hardware interlock. The evaporator fan is energized by relay (K,) controlled by micro-controller (U,) and matched to the compressor for improved efficiency and comfort.

Apparatus and method for control of a heat pump system

A low cost, microprocessor (U,) based motor controller (,) for driving a half-wave, multiple speed, reversible, DC brushless motor (,) directly from standard AC 50/60 Hz power. A large number of different speed and rotation direction combinations may be chosen before or after the motor is installed using configuration resistors (R,, R,). SIDACs (TS,, TS,) each serially connected to a diode (D,, D,) are connected across respective coils (COIL,, COIL,) to clamp the flyback energy in the windings to a few volts when triggered and allow Vemf to float when not triggered. The control adjusts the relative phase timing of commutation during start-up and during running to enhance efficiency. Locked rotor protection is provided by limiting start-up time to a selected period which is followed by a selected cool-off time.

DC brushless motor controller apparatus and method

An electric control is shown adapted for use with gas furnaces which controls fan motors, ignition controls and a gas valve based on inputs from a room thermostat, limit switches, a flame probe, a flame roll-out probe, and a condensate sensor. A roll-out detection circuit utilizing flame rectification includes a multidirectional roll-out probe 16 coupled to a microcontroller (U2) through an inverter (U3) to provide both fault both protection and fault identification. A condensate sensor (20) in the form of a conductive condensate sensor member is also coupled to the microcontroller (U2) through an inverter (U3) to detect the presence of condensate build-up.

Combined fan and ignition control with selected condition sensing

A gas fired furnace system (10) has a controller (14) controlling the supply of gas through a gas valve (12) and air for combustion by means of an induced air draft fan (28), ignition of the gas by means of ignitor (22), the delivery of heated air from a heat exchanger (20) by means of an air blower (34) in response to signals from a thermostat (42). A selected constant flow of air for combustion is provided by controlling the speed of the motor driving the induced motor fan (28) despite changes which may occur in back pressure. Induced draft fan motor parameters proportional to motor torque and motor speed are read on an ongoing basis and inputted to controller (14) which computes a desired voltage and compares that with referenced data stored in the controller memory and makes corrections to the speed of the induced draft fan motor to maintain the constant air flow. The motor speed and motor torque are also monitored to ensure that they are within selected limits indicative of safe operation and responsive to this input energization of a relay (KM1) is controlled to deenergize the gas valve and ignition.

Method for controlling an induced draft fan for use with gas furnaces

Induced draft fan control for use with gas furnaces

An electric control for gas furnaces which controls a two speed main blower fan and an induction draft fan based on inputs from a room thermostat, a high limit and an ignition control including a gas valve. The control has a circuit board having a power supply for providing 24 volts DC current source to drive DC relays and a 5 volt DC power source to power a microprocessor. 24 volt AC input signals are coupled to the input ports of the microprocessor through current limiting resistors and to AC ground through pull down resistors. AC ground is also connected to the IRQ port of the microprocessor. The output ports of the microprocessor are connected to a relay driver which in turn is connected to the relays. Several breakaway tabs in the board provide optional features such as eliminating a normally provided draft delay timing function. Test pads are provided on the board so that the board can be tested during manufacture. An optional feature is shown comprising an LED which can be used to indicate the status of the system. Another optional feature incorporates a zener diode and resistor coupled to each input port to increase input thresholds. This feature is provided for use with power stealing electronic thermostats. The control calibrates itself on a continuing periodic basis to read the AC inputs synchronously at the peak of their wave and switches the relays asynchronously based on the real time clock of the microprocessor.

Furnace control apparatus

An electronic control for gas furnaces controls a two speed main blower fan and an induction draft fan based on 24 volt input signals from a room thermostat, a high limit and an ignition control including a gas valve. The input signals are coupled to input ports of a microprocessor through current limiting resistors and to AC ground through pull down resistors. AC ground is also connected to the IRQ port of the microprocessor. Output ports of the microprocessor are connected to a relay driver which in turn is connected to relays for energizing and de-energizing the fans. The control calibrates itself on a continuing periodic basis to read the AC inputs synchronously at the peak of their wave and can switch the relays asynchronously based on the Real Time Clock of the microprocessor or can be switched synchronously by providing a selected delay so that contact engagement and disengagement occurs at or near the zero crossing of the AC line voltage wave form. When used with resistive loads the relays are switch in response to a signal from the microprocessor which is delayed based on the mechanical switching time constant of the relays to provide contact closure and opening at the selected point on the AC line voltage wave form. An alternate embodiment shows a feedback network used to calibrate the specific delay period for each relay upon initialization. When used with inductive loads contact closing can be effected synchronously and contact opening asynchronously.

Method and apparatus for enhancing relay life

An electric control is shown for gas furnaces which controls fan motors and ignition controls based on inputs from a room thermostat (32), a high limit control and an ignition control (14) including a gas valve. A flame sense circuit (42, 42') is coupled to a microprocessor (U2) and includes a flameprobe (P1) energized by line power through a capacitor (C3) via a quick connect (QC31). A capacitor (C4) is charged by a 5 volt DC source through resistor (R12) and inputted to an inverter (U3, S2) which provides a low signal to the microprocessor when no flame is present. When a flame is present the capacitor (C4) discharges through the flame causing the inverter to change state providing a high to the microprocessor indicating that a flame is present. A diagnostic network comprising a low leakage diode (CR10) and serially connected resistor (R11) is coupled between the microprocessor (pin 8) and the input of the inverter (U3) so that the operation of the flame sense circuit can be tested. In an alternate embodiment CMOS switches (S1, S2) are used both to verify that the flame sense circuit is properly wired and to simulate a no-flame condition.

Self-diagnostic flame rectification sensing circuit and method therefor

A low voltage terminal board interfaces a fan motor with a field thermostat. The board includes a power supply providing a 24 volt DC power source for driving an electronic air cleaner relay and fan motor control lines and a 5 volt DC power source for providing optical isolation and timing logic. Several heater stage signals are connected to a diode interlock network so that no matter which signal is generated the first electric stage heater is energized. A first optically coupled isolator receives a 240 volt AC input whenever the first stage electric heater is energized with the isolator output controlling energization of a heat or medium speed operation of the fan motor. Second and third optically coupled isolators receive a 24 volt AC input indicative of continuous fan operation and compressor operation respectively with the outputs controlling energization of low (on/off) fan speed operation and high speed fan operation respectively. A timing circuit is interconnected between the third optically coupled isolator and the high speed fan terminal to provide a delayed off period of fan operation. Diode interconnections ensure that the on/off terminal is energized anytime the high speed terminal or the first stage electric heater is energized and anytime the on/off line is energized the electronic air cleaner relay is energized.

Interface circuit having improved isolation among signals for use with a

A low-cost, highly-responsive temperature sensor has a thermistor element surface-mounted in a circuit defined by an electrically-conducting layer of a three-layer circuit substrate to be in close thermal coupling to a metal base layer on an opposite side of the substrate. The base layer is adapted to be disposed in heat-collecting relation to a surface whose temperature is to be monitored. An intermediate layer of the substrate has a binder electrically insulating the thermistor from the metal base layer and has thermally-conducting particles dispersed in the binder to improve thermal coupling of the thermistor to the heat-collecting substrate base layer. The circuit defines terminal pads surface-mounting the thermistor element at one end of the substrate and defines interconnected terminal pads at an opposite end of the substrate which are connected to device lead wires in substantial thermal isolation from the thermistor element.

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Berea, KY, United States of America

Mitchell R Rowlette