Solid State Relay Current Protection for Accurate Thermostat Sensing
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Solution Overview
Problem
Smart thermostats face challenges in handling significant electrical power and are susceptible to spikes and overvoltages, requiring reliable operation while being affordable, compact, and maintaining accurate temperature control, which is difficult to achieve due to varying bulk heating effects from components like solid state relays and PCB traces.
Innovation Solution
A control device that measures current flow through solid state relays to determine bulk heating, compensates temperature readings for internal heating effects, and employs multiple safety thresholds to protect relays from overcurrent conditions, ensuring accurate temperature control and reliable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solid state relays are used to switch electrical power in a digital control device, then the device can provide reliable service and control HVAC systems, but the solid state relays are susceptible to damage from electrical spikes and overvoltages
Solution Approach 1:
The patent implements current monitoring that detects overcurrent conditions before they can damage the solid state relays. The system continuously monitors current through the relays and activates protection mechanisms in advance, cushioning the relays against harmful electrical spikes and overvoltages before they cause damage.
Solution Approach 2:
The patent introduces an intermediary current monitoring system between the power source and the solid state relays. This monitoring system acts as a mediator that detects abnormal current conditions and triggers protective actions, preventing direct damage to the relays from electrical spikes and overvoltages.
2Measurement precision
If temperature sensors are placed inside the control device housing to monitor environmental temperature, then the device can control HVAC systems, but the internal components generate bulk heating that corrupts temperature readings
Solution Approach 1:
The patent implements a feedback mechanism where the system continuously monitors the current flowing through solid state relays and calculates the resulting bulk heating. This bulk heating information is fed back to the temperature control algorithm, which then compensates for the heating effect by adjusting the target temperature or control parameters, maintaining accurate temperature control despite internal heat generation.
Solution Approach 2:
The patent changes the parameter used for temperature control by introducing a compensation factor based on bulk heating calculations. Instead of using raw temperature sensor readings directly, the system adjusts the temperature parameter by subtracting the calculated bulk heating effect, thereby maintaining measurement precision despite the presence of internal heat-generating components.
3Ease of manufacture
If the control device is made compact and affordable like consumer electronics, then it meets consumer expectations, but it becomes more susceptible to electrical damage compared to industrial devices
Solution Approach 1:
The patent implements a self-service protection system where the control device monitors its own current consumption and automatically activates protection mechanisms when abnormal conditions are detected. The system uses its own resources (processor, current sensors) to detect and respond to electrical threats, providing reliable protection without requiring external industrial-grade protection circuits, thereby maintaining compactness and affordability.
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
The solution provides more accurate temperature control by accounting for bulk heating and protects solid state relays from damage, enhancing the reliability and efficiency of smart thermostats in managing HVAC systems.
Implementation Method 1
determine the amount of bulk heating produced by the determined amount of current and an associated predetermined electrical resistance
Implementation Method 2
at least one current measuring device to determine the amount of current flowing from the supply of power to the at least one electrical subsystem when the at least one solid state relay is activated
Implementation Method 3
determine the amount of bulk heating produced by the determined amount of current and an associated predetermined electrical resistance
Data Source
AI summary
A control device, such as a smart thermostat, employs solid state relays as switches to activate and deactivate systems controlled by the device. Current flows through at least some of the solid state relays are monitored to determine the bulk heating produced in the solid state relays, and their associated circuitry and printed circuit board traces, and this determined amount of bulk heat is added to other determined amounts of bulk heat and is used to compensate the reading provided by temperature sensors within the control device which have been affected by the bulk heat. Further, by measuring the current flow through the power buses to one or more of the solid state relays of the control device, potentially damaging over current conditions can be distinguished from permissible transient over-current conditions and the control device can deactivate any solid state relays which would be damaged while allowing solid state relays which are experiencing allowable transients to remain operating. In the case of a severe over current condition, a current monitoring device can issue a fault signal, triggering an interrupt condition which will cause a processor in the controller to shut down the affected solid state relays very quickly.