Abstract: An industrial process control transmitter includes a first input configured to couple to a first sensor, and a second input configured to couple to a second sensor. Measurement circuitry is configured to couple to the first and second sensors and provide an output related to a sensed process variable. A multiplexer is configured to selectively couple the first and second sensors to the measurement circuitry. An equalizer circuit is coupled to the first and second sensors and configured to equalize a voltage potential between the first sensor and the measurement circuitry.

Abstract: An assembly includes a thermocouple, a cold junction sensor, and a circuit. The thermocouple has a process end and a cold junction end. The cold junction end has first and second cold junction terminals. The cold junction sensor is supported near the cold junction end and configured to measure temperature at the cold junction end. The circuit is electrically connected to the cold junction sensor and to the first and second cold junction terminals. The circuit is configured to produce a thermocouple signal as a function of voltage across the first and second cold junction terminals and to produce a cold junction sensor signal as a function of temperature of the cold junction end as measured by the cold junction sensor. The circuit is further configured to calculate a correlation between the thermocouple signal and the cold junction sensor signal.

Abstract: An industrial process control transmitter includes a first input configured to couple to a first sensor, and a second input configured to couple to a second sensor. Measurement circuitry is configured to couple to the first and second sensors and provide an output related to a sensed process variable. A multiplexer is configured to selectively couple the first and second sensors to the measurement circuitry. An equalizer circuit is coupled to the first and second sensors and configured to equalize a voltage potential between the first sensor and the measurement circuitry.

Abstract: An assembly includes a thermocouple, a cold junction sensor, and a circuit. The thermocouple has a process end and a cold junction end. The cold junction end has first and second cold junction terminals. The cold junction sensor is supported near the cold junction end and configured to measure temperature at the cold junction end. The circuit is electrically connected to the cold junction sensor and to the first and second cold junction terminals. The circuit is configured to produce a thermocouple signal as a function of voltage across the first and second cold junction terminals and to produce a cold junction sensor signal as a function of temperature of the cold junction end as measured by the cold junction sensor. The circuit is further configured to calculate a correlation between the thermocouple signal and the cold junction sensor signal.

Abstract: A two-wire temperature transmitter performs thermocouple diagnostics on a thermocouple attached to the transmitter to determine if, and the extent to which, the thermocouple has degraded. Various methods of obtaining thermocouple resistance are also provided.

Abstract: A calibrating system calibrates an analog-to-digital converter which has an integrator and first and second reference current sources. A quantity of charge is accumulated in the integrator. The quantity of charge is removed from the integrator by applying the first and second reference currents to the integrator for first and second time periods until the accumulated charge reaches a threshold level. The quantity of charge is reaccumulated in the integrator and again removed by applying the first and second reference currents for third and fourth time periods wherein the first and second time periods are different from the third and fourth time periods. The relative magnitude of the first and second reference currents is determined based on the first, second, third and fourth time periods.

Abstract: A transmitter generates an output signal, which represents temperature, based on potential across thermocouple leads from a main thermocouple. A housing has first and second terminals extending through a wall which separates first and second cavities in the housing. The terminals are connected to the thermocouple leads in the first cavity to form terminal cold junctions. A converter has converter leads which are connected to the terminals in the second cavity. The converter senses a combined signal which represents main thermocouple potential and terminal cold junction potential. The converter also provides the output signal. A conductor has a first end coupled to the first terminal and a second end coupled to the converter forming a correction thermocouple. The correction thermocouple provides a first correction signal representing a difference between a terminal temperature and a converter temperature.

Abstract: A transmitter couples an output to a loop which represents a sensed process variable such as pressure. A microprocessor-based circuit in the transmitter senses the process variable and computes an output signal and provides the output to the loop. A communication circuit in the transmitter receives a high frequency signal including a transmitter parameter from the loop. The communication circuit couples the parameter to the microprocessor. The microprocessor couples the parameter to an EEPROM. The high energization requirements of the EEPROM during a WRITE interval are supplied by an energization circuit. The energization circuit receives energization from the loop at a low rate so that the output is not substantially disturbed. The energization circuit stores energy and supplies energization to the EEPROM during the WRITE time interval without substantially disturbing the loop current.

Abstract: A current source for establishing a relatively constant current through widely differing impedances comprising a voltage potential regulator for adjustably regulating a supplied potential to provide a current to a current controller with a current sensor to supply a signal to the current controller, there being a signal supplied from the signal controller to control the voltage potential regulator. A further current rise time regulator is provided to increase the rise time occurrence provided to a commutated load.

Abstract: A circuit is coupled to an external power supply and is coupled to a non-live zero, two wire DC current transmitter (e.g. 4-20 MA output) for converting such current to a live-zero DC output current signal (e.g. 0-20 MA output) and for powering such transmitter. The circuit has a first current to voltage converter for converting the transmitter current signal to a voltage signal, and a second current to voltage converter coupled to receive the circuit output current signal and an offset current from an offset current source for converting the sum of the circuit output and offset currents to a second voltage signal. A comparator is used for comparing the first and second voltage signals to provide the live-zero output current signal representative of the non-live zero transmitter signal. The circuitry can also provide isolated power to the transmitter and feedback (closed loop) control of such power.