Temperature-measuring-add-on-for-dmm-digital-voltmeter
The DVM-to-temperature adapter is constructed around a single integrated circuit (IC), the National LM10. This micropower IC features a stable 0.2 V reference, a reference amplifier, and a general-purpose operational amplifier. The circuit is designed to operate within a linear temperature range of 0 to 100 °C (32 to 212 °F). The 0.2 V reference and reference amplifier supply a stable, fixed-excitation voltage to the Wheatstone bridge. The voltage is set by a feedback network comprising resistors R1 through R6. Switch S2a adjusts the feedback to increase the voltage from 0.6 V in the Celsius range to 1.08 V in the Fahrenheit range.
These adjustments account for the difference in resistance change per degree between Fahrenheit and Celsius. Resistors R1 through R16 also establish the fixed leg of the Wheatstone bridge, calibrating the bridge output to zero at 0 degrees. Since 0 °C does not equate to 0 °F, switch S2b is utilized to select the correct offset. The LM10's operational amplifier, in conjunction with resistors R9 through R12, forms a differential amplifier that amplifies the bridge output to 10 mV per degree. Given that a single supply is employed and the output must accommodate both positive and negative swings, the output is referenced to the bridge supply voltage rather than the common supply.
The DVM-to-temperature adapter circuit leverages the capabilities of the LM10 IC to provide a precise and stable temperature measurement interface. The core functionality relies on the Wheatstone bridge configuration, which is a common method for measuring resistance changes due to temperature variations. The reference voltage of 0.2 V is critical in ensuring that the Wheatstone bridge operates effectively, providing a consistent excitation voltage that minimizes errors due to fluctuations in the power supply.
The feedback network formed by resistors R1 to R6 plays a vital role in determining the output voltage range, allowing for seamless switching between Celsius and Fahrenheit scales via switch S2a. This adaptability is essential for applications that require temperature readings in different units, ensuring that the system remains versatile and user-friendly.
The differential amplifier configuration, utilizing the operational amplifier within the LM10, enhances the sensitivity of the temperature measurement. By amplifying the output from the Wheatstone bridge to 10 mV per degree, the circuit ensures that even small changes in temperature result in discernible voltage variations, which can be accurately measured by digital voltmeters (DVMs).
The inclusion of switch S2b for offset selection is a thoughtful design consideration, allowing for calibration adjustments that account for the non-linear relationship between Celsius and Fahrenheit scales. This feature ensures that the adapter provides accurate readings across the entire specified temperature range, making it suitable for various applications in scientific research, industrial monitoring, and environmental control systems.
Overall, the DVM-to-temperature adapter exemplifies a well-engineered solution for temperature measurement, integrating advanced circuitry and thoughtful design elements to achieve high precision and reliability.The DVM-to-temperature adapter is built around a single IC, National"s LMlO. That micropower IC contains a stable 0.2 V reference, a reference amplifier and a general-purpose op amp. The circuit is designed for a linear temperature range of 0 to 100°C (32 to 212°F). The 0.2-V reference and reference amplifier provide a stable, fixed-excitation voltage to the Wheatstone bridge.
The voltage is determined by a feedback network consisting of Rl through R6. Switch S2a configures the feedback to increase the voltage from 0.6 Von the Celsius range to 1.08 Von the Fahrenheit range. These differences compensate for the fact that one degree Fahrenheit produces a smaller resistance change than does one degree Celsius. Resistors Rl through R16 also form the fixed leg of the Wheatstone bridge, nulling the bridge output at zero degrees.
Since 0°C is different from 0°F, S2b is used to select the appropriate offset. The LMlO"s op amp, along with R9 through Rl2, form a differential amplifier that boosts the bridge output to 10 m V per degree. Since a single supply is used, and since the output must be able to swing both positive and negative, the output is referenced to the bridge supply voltage, rather than to the common supply.
🔗 External reference
These adjustments account for the difference in resistance change per degree between Fahrenheit and Celsius. Resistors R1 through R16 also establish the fixed leg of the Wheatstone bridge, calibrating the bridge output to zero at 0 degrees. Since 0 °C does not equate to 0 °F, switch S2b is utilized to select the correct offset. The LM10's operational amplifier, in conjunction with resistors R9 through R12, forms a differential amplifier that amplifies the bridge output to 10 mV per degree. Given that a single supply is employed and the output must accommodate both positive and negative swings, the output is referenced to the bridge supply voltage rather than the common supply.
The DVM-to-temperature adapter circuit leverages the capabilities of the LM10 IC to provide a precise and stable temperature measurement interface. The core functionality relies on the Wheatstone bridge configuration, which is a common method for measuring resistance changes due to temperature variations. The reference voltage of 0.2 V is critical in ensuring that the Wheatstone bridge operates effectively, providing a consistent excitation voltage that minimizes errors due to fluctuations in the power supply.
The feedback network formed by resistors R1 to R6 plays a vital role in determining the output voltage range, allowing for seamless switching between Celsius and Fahrenheit scales via switch S2a. This adaptability is essential for applications that require temperature readings in different units, ensuring that the system remains versatile and user-friendly.
The differential amplifier configuration, utilizing the operational amplifier within the LM10, enhances the sensitivity of the temperature measurement. By amplifying the output from the Wheatstone bridge to 10 mV per degree, the circuit ensures that even small changes in temperature result in discernible voltage variations, which can be accurately measured by digital voltmeters (DVMs).
The inclusion of switch S2b for offset selection is a thoughtful design consideration, allowing for calibration adjustments that account for the non-linear relationship between Celsius and Fahrenheit scales. This feature ensures that the adapter provides accurate readings across the entire specified temperature range, making it suitable for various applications in scientific research, industrial monitoring, and environmental control systems.
Overall, the DVM-to-temperature adapter exemplifies a well-engineered solution for temperature measurement, integrating advanced circuitry and thoughtful design elements to achieve high precision and reliability.The DVM-to-temperature adapter is built around a single IC, National"s LMlO. That micropower IC contains a stable 0.2 V reference, a reference amplifier and a general-purpose op amp. The circuit is designed for a linear temperature range of 0 to 100°C (32 to 212°F). The 0.2-V reference and reference amplifier provide a stable, fixed-excitation voltage to the Wheatstone bridge.
The voltage is determined by a feedback network consisting of Rl through R6. Switch S2a configures the feedback to increase the voltage from 0.6 Von the Celsius range to 1.08 Von the Fahrenheit range. These differences compensate for the fact that one degree Fahrenheit produces a smaller resistance change than does one degree Celsius. Resistors Rl through R16 also form the fixed leg of the Wheatstone bridge, nulling the bridge output at zero degrees.
Since 0°C is different from 0°F, S2b is used to select the appropriate offset. The LMlO"s op amp, along with R9 through Rl2, form a differential amplifier that boosts the bridge output to 10 m V per degree. Since a single supply is used, and since the output must be able to swing both positive and negative, the output is referenced to the bridge supply voltage, rather than to the common supply.
🔗 External reference
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