Self-setting circuit for an HVAC controller
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Solution Overview
Problem
Existing HVAC control systems face challenges in ease of use, assembly, construction, and reliability, particularly in ensuring that latching relays remain in a desired state when the power is disconnected, leading to potential energy wastage and uncomfortable conditions.
Innovation Solution
The proposed solution involves a thermostat assembly with a first sub-assembly and a second sub-assembly that can be releasably engaged, where the second sub-assembly includes circuitry to automatically set output terminals to a predetermined state when the first sub-assembly is released, using pull-down and pull-up resistors to control latching relays and ensure they turn off external devices when disconnected.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the thermostat assembly uses a releasable engagement mechanism between first and second sub-assemblies, then ease of assembly and disassembly is improved, but reliability may worsen due to potential connection instability
Solution Approach 1:
The thermostat assembly is divided into two separable sub-assemblies: a first sub-assembly containing the controller and a second sub-assembly containing the output terminals. This segmentation allows easy assembly and disassembly while maintaining reliable connections through dedicated engagement features including alignment pins, snap-fit mechanisms, and electrical contacts that ensure stable electrical connection when engaged.
2Loss of energy
If the circuitry automatically sets output terminals to predetermined state when sub-assemblies are separated, then energy wastage is prevented, but device complexity increases
Solution Approach 1:
The circuitry is configured to automatically detect when the first sub-assembly is separated from the second sub-assembly and preemptively sets the output terminals to a predetermined safe state (such as open circuit or default position) before any HVAC equipment can be affected. This preliminary action prevents energy wastage and ensures system safety without requiring complex additional components, utilizing existing circuit elements to achieve the automatic state transition.
3Measurement precision
If latching relays are used to control HVAC components, then control precision is improved, but reliability worsens when power is disconnected as relays may remain in undesired state
Solution Approach 1:
The circuitry incorporates feedback mechanisms that monitor the state of latching relays and the engagement status of sub-assemblies. When separation is detected, the feedback signal triggers the circuitry to automatically reset the latching relays to their predetermined safe state. This feedback loop ensures that even though latching relays provide precise control during operation, their state is reliably managed during power disconnection or sub-assembly separation, preventing them from remaining in undesired states.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration ensures that latching relays are properly set when the first sub-assembly is disengaged, preventing energy wastage and maintaining desired environmental conditions, thus enhancing the reliability and efficiency of HVAC control systems.
Implementation Method 1
using pull-down and pull-up resistors to control latching relays and ensure they turn off external devices when disconnected
Data Source
AI summary
An HVAC Controller may include a first sub-assembly and a second sub-assembly capable of releasably engaging the first sub-assembly. The first sub-assembly may include a first housing and a printed circuit board having a controller for providing one or more control signals, where the printed circuit board may be secured relative to the first housing. The second sub-assembly may include a second housing, a power source, one or more output terminals, and a second printed circuit board. The second printed circuit board may be secured relative to the second housing and may have circuitry thereon that is powered by the power source and configured to receive the one or more control signals from the first printed circuit board. The circuitry of the second sub-assembly may set output terminals thereof to a predetermined state when the first sub-assembly is released from the second sub-assembly.