# US 5,705,792 A · Digital temperature sensing conditioning and safety system with current control > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,705,792 A - Document ID: US5705792A - Status: Granted - Kind: A - Application number: 08/617,172 - Filed: 1996-03-18 - Granted: 1998-01-06 - Earliest claimed: 1996-03-18 - Assignees: Robertshaw Controls Company - Inventors: Donald W. Graham - Web page: https://patentgrep.com/patent/US5705792A ## CPC - G01K 7/21: for modifying the output characteristic, e.g. linearising - F24C 15/022: {Latches} - G01K: MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR (radiation pyrometry G01J5/00) - F24C: DOMESTIC STOVES OR RANGES (exclusively for solid fuels F24B); DETAILS OF DOMESTIC STOVES OR RANGES, OF GENERAL APPLICATION ## Abstract A temperature sensing system that includes a temperature probe, a signal conditioning circuit, and a microprocessor. The conditioning circuit incorporates a novel dual voltage range measurement technique that improves the accuracy of such systems. The safety circuitry is provided in order to protect against thermal runaway and to inhibit or enable a door lock. ## Claims ### Claim 1 A temperature sensing system, comprising: a signal conditioning circuit connected to a temperature sensing probe; wherein said signal conditioning circuit creates a first signal to control a heater device in response to an input from said temperature sensing probe based on an external variable temperature measurement; a safety circuit connected to said signal conditioning circuit; wherein said safety circuit creates a second signal that operates to disable an oven door lock device above a first maximum temperature level and creates a third signal that operates to disable an oven heater device above a second maximum temperature level; and, a microprocessor connected to said signal conditioning circuit and said safety circuit. ### Claim 2 (depends on 1) A temperature sensing system according to claim 1, wherein said signal conditioning circuit further comprises: a first voltage source; a first operational amplifier stage connected to said first voltage source; wherein said first operational amplifier stage is a voltage-to-current converter; wherein said temperature sensing probe further comprises a resistance temperature detector; wherein said first operational amplifier stage converts the resistance change of said resistance temperature detector into a proportional first voltage signal; a second operational amplifier stage connected to said first operational amplifier stage and a second voltage source; wherein said second amplifier stage is a difference amplifier that compares said second voltage source to a second voltage signal to create said first signal; wherein said second voltage signal is created by dual resistor network voltage divider circuits which include a first switch device to select one circuit at a time and divide said second voltage source. ### Claim 3 (depends on 2) A temperature sensing system according to claim 2, wherein said safety circuit further comprises: a third operational amplifier stage connected to said first voltage source; wherein said third operational amplifier stage is a comparator that compares said first voltage source to a third voltage signal to create said second signal; wherein said third voltage signal is created by dual resistor network voltage divider circuits which divide said first voltage signal; and a fourth operational amplifier stage connected to said first voltage source; wherein said fourth operational amplifier stage is a comparator that compares said first voltage source to a fourth voltage signal to create said third signal; wherein said fourth voltage is created by dual resistor network voltage divider circuits which include a second switch device to select one circuit at a time and divide said first voltage signal. ### Claim 4 A signal conditioning circuit, comprising: a voltage source; a first operational amplifier stage connected to said voltage source; wherein said first operational amplifier stage is a voltage-to-current converter; a temperature sensing probe connected to said first operational amplifier stage; wherein said temperature sensing probe further comprises a resistance temperature detector that is located in a feedback loop of said first operational amplifier stage; wherein said first operational amplifier stage operates to convert a resistance change of said resistance temperature detector into a proportional first voltage signal; and a second operational amplifier stage connected to said first operational amplifier stage and a second voltage signal; wherein said second operational amplifier stage is a difference amplifier that compares said second voltage signal to said proportional first voltage signal to create an output signal to control an oven heater device; wherein said second voltage signal is created by a second voltage source and resistor network voltage divider circuits which include a switch device to divide said second voltage source. ### Claim 5 A safety circuit, comprising: a first operational amplifier stage connected to a first voltage source; wherein said first operational amplifier stage is a comparator that compares said first voltage source to a first voltage signal to create a first digital signal to control an oven door lock device; wherein said first voltage signal is created by a resistor network voltage divider circuit which divides a second voltage source; and a second operational amplifier stage connected to said first voltage source; wherein said second operational amplifier stage is a comparator that compares said first voltage source to a second voltage signal to create a second digital signal to control an oven temperature limiting device; wherein said second voltage signal is created by dual resistor network voltage divider circuits which include a switch device to select one circuit at a time and divide said second voltage signal. ### Claim 6 A method for converting an input temperature signal into output voltage signals, the method comprising: receiving an input temperature signal; applying said input temperature signal to a temperature sensing probe to create a proportional resistance value in said probe; applying said resistance value to a first operational amplifier stage that is a voltage-to-current converter to convert said resistance value into a proportional first voltage signal; applying a first voltage source to two resistor network voltage divider circuits which include a first switch device to select one circuit at a time and divide said voltage source signal to create a second voltage signal; applying said first voltage signal to a second operational amplifier that is a difference amplifier to convert said first voltage signal into a third voltage signal by comparing said first voltage signal to said second voltage signal; processing said third voltage signal into a digital signal to control an oven heater device; applying said first voltage signal to a resistor network to create a fourth voltage signal; applying said first voltage source to a third operational amplifier stage that compares said first voltage source with said fourth voltage signal to create a fifth voltage signal; processing said fifth voltage signal into a digital signal to control an oven door lock device; applying said first voltage signal to dual resistor voltage divider circuits which include a second switch device to select one circuit at a time and divide said first voltage signal to create a sixth voltage signal; applying said first voltage source to a fourth operational amplifier stage that compares said first voltage source with said sixth voltage signal to create a seventh voltage signal; and processing said seventh voltage signal into a digital signal to control an oven heater over-temperature limit device. ### Claim 7 A temperature sensing system, comprising: a temperature sensor, wherein said temperature sensor means is a resistance temperature detector; a first operational amplifier connected to said temperature sensor and a first voltage source, wherein said first operational amplifier includes a voltage-to-current converter with an output proportional to the temperature sensor output; a second operational amplifier connected to said first operational amplifier, wherein said second operational amplifier converts said first operational amplifier output into a third voltage signal by comparing said first operational amplifier output to a second voltage signal; a dual resistor network voltage divider circuit connected to said second operational amplifier, said divider circuit including a first switch for selecting one circuit at a time and dividing said first voltage source to create said second voltage signal; a third operational amplifier connected to said first voltage source; wherein said third operational amplifier compares said first voltage source with a fourth voltage signal to create a fifth voltage signal; wherein said third operational amplifier is connected to a dual resistor network voltage divider circuit for processing said first voltage signal into said fourth voltage signal; and a fourth operational amplifier connected to said first voltage source; wherein said fourth operational amplifier compares said first voltage source with a sixth voltage signal to create a seventh voltage signal; wherein said fourth operational amplifier is connected to a dual resistor voltage divider circuit which includes a second switch for selecting one circuit at a time and dividing said first voltage signal to create said sixth voltage signal; and a processor connected to said second, third and fourth operational amplifier; wherein said processor converts said third voltage signal into a first digital signal to control an oven heater and converts said fourth voltage signal into a second digital signal to control an oven door lock, and converts said seventh voltage signal into a third digital signal to control an oven heater over-temperature limit.