Patent Application
20080054084
First controller 20 provides one or more control functions that may include, but are not necessarily limited to, energizing blower 12, energizing a compressor or valves associated with heat exchanger 14, receiving a feedback signal 26 from thermostat 24, transmitting an output signal 28 to thermostat 24, and receiving various input signals 32 from temperature sensors, pressure sensors, manual input switches, etc. that are installed in the general vicinity of unit 10. Feedback signal 26 received from thermostat 24 via wires 30 may include, but is not limited to, temperature set points, room temperature reading, system parameters, and various other inputs 34. Output signal 28 transmitted from controller 20 to thermostat 24 via wires 30 may include, but is not limited to, temperature set points, outdoor air temperature reading, temperature reading of supply air 36, temperature reading of return air 38, system faults and error messages, and system parameters.
Second controller 22 provides one or more control functions that may include, but are not necessarily limited to, receiving output signal 28 from first controller 20, transmitting feedback signal 26 to controller 20, receiving various input signals 34 from temperature sensors, pressure sensors, manual input switches, etc. that are installed in the general vicinity of thermostat 24. Second controller 22 can also provide an output signal 40 that can be used for controlling a visual display 42 on thermostat 24. Display 42 can indicate various conditions occurring at unit 10 and/or thermostat 24. Examples of such conditions include, but are not limited to, the temperature of return air 38, the temperature of supply air 36, a setpoint temperature, a diagnostic message 44 pertaining to unit 10, the room temperature in the vicinity of thermostat 24, setup parameters of unit 10, etc.
A power supply line 46 of the building can supply electrical power to unit 10 and its controller 20. Wires 30 convey some of that electrical power to energize thermostat 24 and its controller 22, thus wires 30 convey both communication and electrical power, but not at the same time.
To ensure reliable communication between controllers 20 and 22, control system 18 employs a current loop circuit that is inherently noise immune and tolerant of wire impedance. To avoid signal interference, control system 18 selectively operates in three distinct modes: a power mode for conveying electrical power along wires 30, an output mode for conveying output signal 28, and a feedback mode for conveying feedback signal 26. Electrical power, output signal 28 and feedback signal 26 are each conveyed independently of the others. In a currently preferred embodiment, first controller 20 includes a conventional microprocessor 56 that determines which operating mode is in effect, and second controller 22 includes another conventional microprocessor 58 that responds accordingly.
In addition to microprocessor 56, first controller 20 includes a current source circuit 60, a current interrupter 62, and a signal converter 64. A conventional voltage regulator provides 12-VDC at a point 66, and 5-VDC at points 68 and 70. In this particular example, circuit 60 can deliver about 15 mA of current to first terminal-A 48. During the power mode, wires 30 convey that current to power second controller 22. That current is also used for charging an energy storage circuit 72 that powers second controller 22 while the current from circuit 60 is interrupted during the output mode or feedback mode.
In the output mode, current interrupter 62 responds to an output signal 28′ from microprocessor 56 to controllably interrupt the current through wires 30, whereby wires 30 can transmit data (corresponding to output signal 28′) in a standard asynchronous, 19,200-baud method. The “start” and “0” valued bits can be defined as current generally less than 7 mA. The “stop” and “1” valued bits can be defined as current generally greater than 7 mA. Signal converter 64 senses the current level and converts it to standard logic levels.
Second controller 22 includes microprocessor 58, energy storage circuit 72, a current limiter 74, a current interrupter 76, and a signal converter 78. In this example, energy storage circuit 72 includes a conventional voltage regulator 80 operating in conjunction with one or more power storage capacitors 82 and 84 (e.g., 220 uF each). Voltage regulator 80 has a voltage input 86, a regulated DC voltage output 88 (e.g., 3.3 VDC), ON/OFF switch input 90 and a ground 92. If desired, additional capacitors (e.g., 0.1 uF) can be added to drain high frequency noise and voltage transients from point 88 to point 92. As explainer earlier, energy storage circuit 72 is charged during the power mode by at least some of the 15 mA from current source 60, the stored power can then be used for powering second controller 22 (including microprocessor 58) during the output mode and feedback mode.
As wires 30 convey current from controller 20 to controller 22, current limiter 74 and Zener diode 94 help regulate that current at about 15 mA. To guard against voltage spikes, transient voltage suppression diodes 96 and 98 can be installed between wires 30a and 30b. Second controller 22 includes a full wave bridge rectifier 100 that allows the communication and power link between controllers 20 and 22 to be insensitive to the wiring polarity of wires 30.
In response to feedback signal 26′, current interrupter 76 interrupts the current in wires 30 in order to communicate feedback signal 26 to first controller 20. The “start” and “0” valued bits can be defined as current less than 7 mA. The “stop” and “1” valued bits can be defined as current greater than 7 mA.
Signal converter 78 detects the presence and absence of current as a serial data stream and converts it to the logic levels required by the remote thermostat's controller 22.
Although the actual circuit of control system 18 may vary, in a currently preferred embodiment, system 18 includes resistors R1-R18. Resistors R1 and R2 are 100-ohms, resistors R3 and R4 are 47.5-ohms, and resistors R5-R18 are each 11 kilo-ohms.
In the power mode, microprocessor 56 does not provide any pulsed signal at a main transmit point 102, and microprocessor 58 does not provide any pulsed signal at a remote transmit point 104, thus a remote receive point 106 and a main receive point 108 remain at a generally constant level of “HI,” whereby generally no communication occurs between controllers 20 and 22. In the power mode, first terminal-A 48 remains relatively “HI” to charge energy storage circuit 72.
In the output mode, output signal 28′ is communicated from main transmit point 102 of microprocessor 56 to remote receive point 106 on microprocessor 58. At point 106, output signal 28′ is read as output signal 28″. In the output mode, the chart of
In the feedback mode, feedback signal 26′ is communicated from remote transmit point 104 of microprocessor 58 to main receive point 108 on microprocessor 56. At point 108, feedback signal 26′ is read as feedback signal 26″. In the feedback mode, the chart of
Although the invention is described with respect to a preferred embodiment, modifications thereto will be apparent to those of ordinary skill in the art. Control system 18, for instance, does not necessarily have to be used for controlling a PTAC unit, but could be applied to any type of HVAC equipment. Therefore, the scope of the invention is to be determined by reference to the following claims.
