Thermal measuring and testing – Temperature measurement – In spaced noncontact relationship to specimen
Patent
1989-09-07
1991-01-22
Will, Thomas B.
Thermal measuring and testing
Temperature measurement
In spaced noncontact relationship to specimen
374128, 374130, 374133, G01J 510
Patent
active
049866729
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a radiation thermometer.
Radiation thermometers typically include a radiation sensor which generates in response to incident radiation an electrical signal in the form of a voltage or current which passed to a remote detector which in turn generates a signal representative of the temperature of the object from which the radiation has been emitted. The sensor is powered from a remote source. One of the problems with these radiation thermometers is the fact that the electrical signal is subject to "pick-up" and earthing problems and thus can be modified before it reaches the detector. Moreover, electrical connections are difficult to reconcile with regulations applied to "inflammable atmosphere" areas, in which radiation thermometers may be used.
In accordance with the present invention, a radiation thermometer comprises a housing within which are mounted a radiation detector system including a radiation sensor positioned to receive radiation through a window in the housing, the system generating an electrical signal related to the sensed radiation an optical signal generator responsive to the electrical signal from the radiation detector system, an internal temperature detector for generating a signal related to the temperature of the thermometer, wherein the optical signal generator generates an optical signal whose frequency is related to the signal from the radiation sensor and whose mark-space ratio is related to the signal from the internal temperature detector, and wherein the housing is connectable with an optical waveguide into which the optical signal is coupled in use, and a power source connected to the detector system to constitute the sole source of power to the detector system.
This thermometer deals in a particularly simple manner with the problems mentioned above by providing all the electrical equipment, including the power source, within a single housing and without any electrical connections outside the housing. This avoids the pick up and earthing problems mentioned above since the signal passed to the remote detector will be optical.
Furthermore, the invention also permits the thermometer to be used in inflammable atmosphere areas. This can be achieved by selecting low-power consumption components together with a conventional long-life battery constituting the power source which will allow continuous operation for several years. In addition, or alternatively, the housing could be sealed. In this context, by "sealed" we mean that air or gases do not enter the housing.
The radiation sensor is preferably an infrared sensor such as a silicon photo-diode, germanium photodiode, or thermopile.
Conveniently, the detector system further comprises an amplifier to which signals from the radiation sensor are fed for amplification prior to being fed to the optical signal generator.
The optical signal generator conveniently comprises a light emitting diode.
In order to generate the modulated optical signal, the optical signal generator may comprise a modulating system for imposing a frequency modulation on the optical signal generated by the optical signal generator. For example, where the radiation sensor generates a voltage output signal, the optical signal generator may include a voltage to frequency converter. In other examples, the optical signal generator may be arranged to modulate the optical signal with a frequency related to the square root of the received voltage signal.
Typically, the radiation sensor will generate a voltage signal proportional to radiance of a target In theory, this could be used directly in a receiver to determine target temperature. However, the voltage signal could be modified due to the temperature of the thermometer itself and so to deal with this the thermometer includes the internal temperature detector.
Conveniently, the internal temperature detector comprises a thermistor bridge.
Preferably, the optical signal generator includes a comparator to respective input ports of which the signals from the radiation sensor and internal temperature
REFERENCES:
patent: 3940987 (1976-03-01), Green et al.
patent: 4012633 (1977-03-01), Huntley
patent: 4495416 (1985-01-01), Mason et al.
patent: 4633523 (1986-12-01), Witkover
"An Optically Linked Telemetry System for Use with Electromagnetic Field Measurement Probes" Bassen et al., IEEE Transactions on Electromagnetic Compatibility, vol. EMC 20, No. 4, Nov. 1978, pp. 483-488, (340/870.29).
"A Device for the Remote Sensing of Temperature of High Voltage Transmission Collott, Conductor", IEEE Transactions on Industrial Electronics and Control Instrumentation, vol. IECI-28, No. 2, May 1981, pp. 116-119.
Land Infrared Limited
Will Thomas B.
Worth W. Morris
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