Communications: electrical – Continuously variable indicating – With particular transmitter
Patent
1993-03-29
1995-09-19
Peng, John K.
Communications: electrical
Continuously variable indicating
With particular transmitter
34082554, 34082572, G08C 1906
Patent
active
054519390
DESCRIPTION:
BRIEF SUMMARY
SUMMARY OF THE INVENTION
This invention relates to a transmitter and in particular but not exclusively to a temperature transmitter for use with a thermocouple temperature sensor.
It is known to provide "two wire" current transmitters for remote monitoring of physical variables such as temperature or pressure, the transmitters typically being located close to a sensor and connected by two wires to a DC voltage source located at a remote monitoring station such conventional transmitters have the advantage of requiring only two wires to connect them to the remote monitoring station and include current modulating circuitry to transmit a signal along the wires representative of the sensed variable.
"Smart" transmitters are also known which include a microprocessor which can be programmed to adapt the dynamic range of the transmitted signal to suit a required measurement range of the variable and to include calibration data for the selected sensor.
Such smart transmitters have hitherto been interactively programmable by means of an interface unit connected to the wires intermediate the transmitter and the remote monitoring station or located at the station itself, communication with the transmitter being by signals conducted by the wires.
According to the present invention there is disclosed a transmitter for connection to a source of DC voltage via supply wires and to a sensor having definable characteristics for electrical measurement of a physical variable, the transmitter having a housing having terminals for connection to the supply wires and containing transmitter circuitry operable to modulate current in the supply wires to thereby transmit a signal representative of the sensed value of the physical variable; the transmitter circuitry including a microprocessor and a memory for containing data defining a transfer characteristic to be operated by the microprocessor so that the signal is representative of the sensed value or of a predetermined function of the sensed value for said characteristics of the sensor; the transmitter further including a communication means for receiving signals relating to said data defining the transfer characteristic from an electronic programming device, and means to load said data into the memory in response to the signals received by the communication means wherein the communication means comprises an inductive loop.
An advantage of such an arrangement is that it is not necessary for signals for the input of data to the microprocessor to be received through externally mounted electrical terminals on the transmitter so that such terminals can therefore be made less susceptible to radio frequency interference and the input of spurious signals. The number of terminals required on the transmitter can also be minimised.
In a preferred embodiment the external shape of a temperature transmitter corresponds to the dimensions of conventional transmitters so as to be compatible with existing fittings and to conform to established standards.
Advantageously the loop is a coil mounted in the housing of the instrument so as to define an aperture into which a finger of the programming device can be inserted to send signals to the communication means.
The housing may include a metal member having an aperture and the coil may then be mounted behind the periphery of the aperture. The presence of the metal member makes the coil very insensitive to stray fields since the metal member is effectively a shorted coil. This is important where the transmitter is to be used in the presence of stray electromagnetic fields which might otherwise result in corruption of the stored data or could interfere with the operation of the circuitry.
Preferably the housing includes further terminals for connection to sensor wires connected to or forming the sensor, which wires are received in the aperture in the metal member when so connected, the relative dimensions of the aperture and the finger being such that the finger cannot be inserted in the aperture when the sensor wires are so received. The presence of t
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patent: 4801924 (1989-01-01), Burgmann et al.
patent: 4824378 (1989-04-01), Betz
patent: 5077547 (1991-12-01), Burgmann
Fisher-Rosemount Limited
Peng John K.
Wu Daniel J.
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