Transducer interfaces

Details Transducer interfaces Transducer interfaces

1987-07-16

1989-05-16

Shoop, Jr., William M.

Coded data generation or conversion

Analog to or from digital conversion

Analog to digital conversion

341142, 341155, 341169, H03M 156

Patent

active

048313807

DESCRIPTION:

BRIEF SUMMARY
This invention relates to an interface for an electrical transducer which enables measurement errors in the transducer to be corrected during use of the transducer.
In this context the term `error` should be interpreted as any deviation or discrepancy between the measured value of the parameter under observation and its true value, the term error correction means any form of processing required to correct the measured value back to the true value i.e. signal conditioning.
Broadly speaking, transducer measurement errors fall into three classes. A. Errors produced by changes in the operating environment of the transducer e.g. changes in supply voltage, changes in temperature, changes in any environmental parameter other than that which is the primary parameter of investigation that may alter the measured value of the primary parameter. B. Errors produced by variations in characteristics of individual transducers of one class. These may be caused by spreads in manufacturing tolerances, errors in the manufacturers calibration processes, the long term effects of ageing in an individual transducer. C. Class errors, these are characteristic errors of a given class of transducer. For instance all basic thermistor type gas flow monitoring transducers have a non linear output due to the thermistor characteristics and the principle of operation. Again, most semiconductor pressure transducers exhibit a non linear response over some portion of their range due to a decrease in diaphragm compliance with increasing deviation from the resting (zero displacement) state.
In the past there have been two common methods of correcting such errors.
1. Analogue signal conditioning of the transducer either by means of components in its associated circuitry or by components forming an integral part of the transducer and adjusted by the transducer manufacturer.
2. Where the transducer is employed with a microprocessor or computer, data obtained by testing an individual transducer and relating to that transducer may be entered in the memory of the microprocessor or computer and used to correct the transducer errors whenever a reading is taken. In some cases a microprocessor may be required in proximity to the transducer to provide local corrections.
There are disadvantages to both systems, analogue signal conditioning requires that the necessary correction components are designed into the circuitry associated with the transducer and that the whole circuit (including the transducer) should be subjected to repeated cycling through the expected operating conditions in order that it may be adjusted correctly. This will increase production time and expense and unless the correction circuitry is fairly elaborate will not result in extreme accuracy.
The use of a microprocessor or computer, although allowing greater accuracy, limited only by the accuracy of the test equipment, suffers from the disadvantage that if it becomes necessary to exchange the transducer then the correction data stored in the microprocessor or computer must also be changed. In addition to this, where a number of transducers are controlled by a single microprocessor or computer it is necessary to store the relevant data for each transducer in a set of tables held by the microprocessor computer thus limiting (by the amount of memory available for this purpose) the number of transducers that a microprocessor or computer of a given size may control.
Accordingly the present invention provides an addressable transducer interface which may be associated with a particular electrical transducer, having means for storing correction data for the correction of errors as herein defined relating to that transducer so that on addressing of the interface by external control means, the correction data may be transmitted to the control means together with measurement data from the transducer.
Preferably said error correction data is stored in digital form.
Preferably the interface includes an analogue to digital convertor arranged to convert an analogue output signal of the particular t

REFERENCES:
patent: 3701145 (1972-10-01), Bergin
patent: 4031530 (1977-06-01), Aneshansley
patent: 4503707 (1985-03-01), Rosa et al.
patent: 4675649 (1987-06-01), Forehand et al.

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