The present invention relates generally to process sensor systems, and more particularly to thermowell sensor housings for fluid sensors in industrial process monitoring systems.
Industrial process transmitters and sensor assemblies are used to sense various characteristics of process fluids flowing through a conduit or contained within a vessel, and to transmit information about those process characteristics to a control, monitoring and/or safety system remotely located from the process measurement location. Each process transmitter may be connected to one or more sensor and/or actuator assembly. Sensor assemblies may sense a variety of process parameters, including pressure, temperature, pH or flow rate. Process transmitters are typically electrically connected sensor assemblies via sensor wires used to transmit current- or voltage-based analog sensor output signals reflecting at least one such process parameter. Each transmitter reads these sensor output signals, and converts them into a digital measurement of the process parameter. Finally, the transmitter sends the information to the control system.
Sensor assemblies for sensing process fluid temperatures and changes in temperature commonly include at least one temperature sensor housed in a thermowell extending into the fluid flow. Thermowells are designed to be in physical contact with process fluids and to shield the temperature sensor from physical damage caused by direct contact with the fluid, e.g., impacts, corrosion, etc., while efficiently conducting heat between the fluid and the temperature sensor. Thermowells may sometimes vibrate as a result of process fluid flow, and tend to act as thermal barriers that lengthen sensor response times by increasing the thermal mass of the sensor assembly. Some sensor assemblies have included damping fluids such as mineral oils to improve thermal conduction between thermowells and temperature sensors, and to protect alleviate thermowell vibration.