An RTD (resistance temperature sensor or detector) sensing device which is a long, thin, unitary device adapted to be distributed across an extended field for the continuous, uninterrupted sensing or interrogation of such field, avoiding the inaccuracy, unreliability, and excessive expense of conventional "point" RTD and thermocouple sensors currently employed for this purpose. According to the invention, a very long, thin, ductile protective metal outer sheath houses a coextensive body of insulation material, which in turn supports and electrically insulates one or more coextensive RTD filaments and in most forms of the invention one or more heater filaments. Distributed RTDs of the invention may, along their lengths, have continuous linear function sensitivity, continuous variable function sensitivity, or step function sensitivity. Distributed RTDs of the invention have particular utility for gauging liquid level, measuring average mass flow velocity of fluids in large ducts, and sensing the average temperature of an extended nonisothermal field.
In the manner of a tubular heater, a temperature sensor comprises a metallic tubular jacket with internal resistance wire coil embedded in insulating material and closing pieces having electrical connection members, so that a very simple, robust and high temperature-resistant temperature sensor with a measuring range up to e.g. approximately 750.degree. C. is obtained. The temperature sensor jacket can be earthed or grounded. For operating the temperature sensor there is appropriately a test current in the mA range in the case of a test voltage in the mV range, whose temperature-dependent changes are processed by means of an electronic amplifier.
An RTD assembly includes a resistance temperature detector having two outputs, and a pair of electrical conductors including a first end and a second end. The electrical conductors are electrically connected at the second end thereof to the outputs of the resistance temperature detector. An electrically insulating polytetrafluoroethylene body, such as Teflon.RTM., includes a closed end, a cavity and an open end. The resistance temperature detector is disposed within the cavity of the electrically insulating body and proximate the closed end thereof. The electrical conductors extend from the cavity of the electrically insulating body with the first end of the electrical conductors being external to the electrically insulating body. A cured potting compound is disposed within the cavity of the electrically insulating body and about the resistance temperature detector and the second end of the electrical conductors.
A gas sensor having a sensor element which is immobilized in gas-tight fashion in a metal housing. The gas sensor has a double-walled protective tube with an outer protective sleeve and an inner protective sleeve, each of which possesses openings for the entry and/or exit of gas. The inner protective sleeve forms a gas space into which the sensor element projects with a section at the measurement-gas end. The outer protective sleeve is a sleeve having a closed enveloping surface, the openings for the entry and/or exit of gas being arranged in the cavity at the end face of the sleeve. The gas space formed by the inner protective sleeve has, perpendicular to the extension direction of the sensor element, a rectangular cross section.
A thermal dispersion switch/transmitter for determining flow rate and liquid level in a non-contacting apparatus. A special preparation of one or more small spots in the outside surface of the wall of the conduit, standpipe or container enables one or more thermally sensitive elements to reside very close to the fluid on the opposite side of the wall. A temperature sensor is formed of a raster pattern electrical conductor deposited on a thin, electrically insulative, thermally conductive flat chip. One temperature sensor is time-shared and is periodically self heated and functions as the reference as well as the active or heated sensor of the invention. One alternative is to employ two temperature sensors, one being a reference sensor and the other being the active sensor. An alternative embodiment employs the same construction of one or more small, very thin membrane surfaces to which multiple detectors are mounted inside a probe inserted into the conduit. A second alternative embodiment employs the same construction of a very thin, small area spot on the outside of a probe inserted into a conduit or vessel for flow rate, liquid level, or interface sensing. Other embodiments are shown and described. All of the embodiments employ a miniature temperature sensor with the sensing element being self heated, the switch/transmitter being configured to operate at intrinsically safe, 24 VDC, 4-20 mA input power.
A thermal dispersion switch/transmitter for determining flow rate and liquid level in a non-contacting apparatus. A special preparation of one or more small spots in the outside surface of the wall of the conduit, standpipe or container enables one or more thermally sensitive elements to reside very close to the fluid on the opposite side of the wall. A temperature sensor is formed of a raster pattern electrical conductor deposited on a thin, electrically insulative, thermally conductive flat chip. One temperature sensor is time-shared and is periodically self heated and functions as the reference as well as the active or heated sensor of the invention. One alternative is to employ two temperature sensors, one being a reference sensor and the other being the active sensor. An alternative embodiment employs the same construction of one or more small, very thin membrane surfaces to which multiple detectors are mounted inside a probe inserted into the conduit. A second alternative embodiment employs the same construction of a very thin, small area spot on the outside of a probe inserted into a conduit or vessel for flow rate, liquid level, or interface sensing.
