EP0065572A1 - Circuit de linearisation - Google Patents

Circuit de linearisation

Info

Publication number
EP0065572A1
EP0065572A1 EP19820900241 EP82900241A EP0065572A1 EP 0065572 A1 EP0065572 A1 EP 0065572A1 EP 19820900241 EP19820900241 EP 19820900241 EP 82900241 A EP82900241 A EP 82900241A EP 0065572 A1 EP0065572 A1 EP 0065572A1
Authority
EP
European Patent Office
Prior art keywords
voltage
linear
circuit
resistor
linearity
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP19820900241
Other languages
German (de)
English (en)
Inventor
Joseph J. Durkin
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Ametek Inc
Original Assignee
Ametek Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Ametek Inc filed Critical Ametek Inc
Publication of EP0065572A1 publication Critical patent/EP0065572A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
    • G01R15/005—Circuits for altering the indicating characteristic, e.g. making it non-linear

Definitions

  • This invention relates in general to a linearization circuit, and more particularly, to a voltage ramp circuit adapted for linearizing a non-linear voltage ramp input having a positive or negative nonlinearity.
  • an electrical output signal i.e., a voltage ramp
  • the electrical output signal can be used to operate a recording device such that a record can be made of the magnitude and variations in the measured parameter; and, as a control signal indicative of the magnitude of the measured parameter for use within a process control system to effect desired changes in the process .
  • the electrical output signal can also be used to directly control measuring instrumentation such that the magnitude of the measured parameter can be readily determined at any given time and variations thereof noted.
  • transducer elements such as piezoelectric strain elements, linear variable differential transformers, and the like
  • the transducer element typically has a transducer parameter, such as resistance, which changes in magnitude relative to a reference value responsive to variations in the physical parameter being measured. These changes in the transducer parameter can be measured and used to provide the electrical output signal.
  • transducer parameter such as resistance
  • a transducer element For example, if a transducer element provides a one-volt electrical output signal for one-unit of the parameter being measured, it should provide a one-half volt electrical output signal for one-half unit of the measured parameter.
  • the prior art transducer elements generally produce an electrical output signal that is a non-linear function of the parameter being measured. This non-linearity results in the magnitude of the measured parameter being inaccurate, which has heretofore caused problems in the use of conventional transducer elements in a precision instrumentation and control system.
  • Patent No. 3,358,501 one or more additional semiconductor strain elements arranged in a T-network have been used to compensate for the non-linear operation of a strain transducer; and, in U.S. Patent No. 3,283,923 a pair of varactor diodes have been used to compensate for movement of the core in a linear variable differential transformer.
  • a diode connected across the output has been used as has the well-known root extractor circuit utilizing an operational amplifier and transistor between the input and output.
  • Another object of the present invention is to provide a linearization circuit which linearizes a voltage input having a negative bow, positive bow or S-shaped bow non-linearity.
  • a linearization circuit for producing a predictable non-linear voltage ramp in response to a non-linear input voltage.
  • the circuit includes a divider network and means operatively coupled to at least one element of the divider network selected to provide a non-linear voltage having a predetermined amount of non-linearity for producing a linear output voltage in response to the non-linear input voltage.
  • the dividing network is a resistance divider. Coupled across one of the resistors in the divider network is a series connected resistor and diode. The resistance value of the resistor is chosen so that voltage across the diode compensates for the non-linear input voltage thereby producing a linear output voltage.
  • FIG. 1 is a graph showing an ideal linear voltage ramp and non-linear voltage ramps having positive bow, and S-shaped bow non-linearity for which compensation is provided by the linearization circuit of the present invention
  • FIGS. 2a and 3 through 6 are circuit diagrams of various embodiments of the linearization circuit according to the present invention which provide compensation for the non-linear voltage ramps shown in FIG. 1;
  • FIG. 2b is a Thevenin equivalent circuit diagram of the circuit shown in FIG. 2a.
  • FIG. 7 is a combined block and circuit dia gram of a transducer system incorporating the linearization circuit of the present invention.
  • the linearization circuit of the present invention is adapted to generate a predictable non-linear voltage having a predetermined amount of non-linearity to compensate for a non-linear input voltage and thereby providing a linear output voltage.
  • Fig. 1 is a graphical representation showing possible voltages which may be produced, for example, by a pressure transducer measuring applied pressure. The ideal voltage would be linear. However, in practice, the voltage would have a positive bow, a negative bow or be S-shaped.
  • the linearization circuit generates a predictable non-linear input voltage and produces an output which approaches the desired ideal linear voltage.
  • the linearization circuit of the present invention includes a resistor voltage divider having a first resistor RA and a second resistor RB.
  • resistors RA, RB is shunted by the series combination of resistor RS and diode CR1 which produces a non-linear voltage ramp having a predetermined amount of non-linearity.
  • the polarity of the voltage determines the polarity of insertion of the diode CR1. if a positive voltage having a negative bow is to be linearized, resistor RB is shunted by the series combination of resistor RS and diode CR1 as shown in FIG. 2a.
  • resistor RA is shunted by the series combination of resistor RS and diode CR1 as shown in FIG. 3.
  • negative and positive bow linearization are provided respectively by the circuits of FIGS. 4 and 5.
  • resistor RA and resistor RB are shunted by a series combination of resistors RS1, RS2 and diodes CR1, CR2 as shown in FIG. 6.
  • the theory of operation of the linearization circuit in accordance with the present invention can be explained by reference to FIG. 2a.
  • the input voltage V in is typically provided from a transducer element and is a non-linear voltage proportional to the measured parameter normalized over a desired full scale range, for example, 0 to 2.0 volts.
  • An increasing input voltage from the transducer element produces a current through resistor RS, which current, I D also flows through diode CR1.
  • the diode current I D is directly proportional to the diode voltage V D which can be operatively controlled to be non-linear when by maintaining the diode voltage between the turn-on voltage and the saturation voltage of the diode. For example, where a conventional silicon diode is used, this non-linear operating range of the diode will be generally about from 0.2 volts to 0.7 volts.
  • the diode voltage V D can be determined which generates a non-linear voltage, equal in magnitude and opposite in polarity to the applied input voltage, thus producing an linear voltage output, V out .
  • CR1 is determined by the value of resistor RA and resistor RB in the voltage divider circuit.
  • the values of resistor RA and resistor RB are selected to cause the voltage drop across resistor RS and diode CR1 to be generally within the non-linear operating range of diode CR1.
  • the value of RA is selected to be equal to the value of RB. If the voltage drop across resistor RS and diode CR1 is greater than the saturation voltage of diode CR1, the diode Voltage V D will be linear and the circuit will function as a conventional linear voltage divider. If the voltage drop across resistor RS and diode CR1 is less than the turn-on voltage of diode CR1, the circuit will also generate a linear voltage.
  • the non-linearity of the voltage generated by a transducer element is symmetrical about an ideal linear voltage.
  • the maximum error of the non-linear voltage from the ideal voltage will therefore occur at 50% of the normalized full scale.
  • resistor RA and resistor RB such triat the voltage drop across resistor RS and diode CR1 is within the operating range of the diode, the maximum error from the ideal voltage ramp will occur at about 50% of full scale.
  • the non-linearity of the input voltage is not symmetrical about an ideal linear voltage, the maximum error will occur at other than 50% of full scale.
  • the voltage drop across resistor RS and diode CR1 is provided partially within the linear operating range of the diode causing the maximum error to be shifted either upward or downward an appropriate amount. If the voltage drop across resistor RS and diode CR1 is less than the turn-on voltage of the diode, the maximum error will be shifted downward from 50% of full scale and if the voltage drop is greater than the diode saturation voltage, the maximum error will be shifted upward from
  • FIG. 2b where:
  • resistor RS The proper value for resistor RS can be determined by solving Equations 1 and 2 such that resistor RS in combination with diode CR1 will have a voltage dependent parallel shunting effect on resistor RB to cause the linearization circuit to generate the desired voltage having a predetermined amount of non-linearity.
  • the equations for the output voltage V out as a function and the input voltage V in for the linearization circuits of FIGS. 3-6 can be derived in a similar manner and would be known to those having ordinary skill in the art by the application of the principles of the present invention disclosed with reference to FIGS. 2a and 2b.
  • the appropriate value for RS can be determined as follows.
  • the normalized uncompensated voltage output from the transducer element is determined at selected percentages of full scale, such as at 0%, 25%, 50%, 75% and 100%.
  • Equation 1 normalized uncompensated voltages, V in are entered into Equation 1 in addition to values for q, k, T, and resistor RA, resistor RB, I O of the specific diode used, and an initial estimated value for resistor RS.
  • Equation 1 is solved for the diode voltage V D for each of the normalized uncompensated voltage readings.
  • the corresponding diode voltages V D are entered into Equation 2 to solve for the output voltage V out of the linearization circuit.
  • the percentage error is calculated and the resulting maximum full scale error determined. Equations 1 and 2 are again solved using a different estimated value for resistor RS until the resulting maximum full scale error is determined to be a minimum value.
  • resistor RS which generates a minimum full scale error is used in the linearization circuit in combination with the selected diode CR1.
  • Resistor RA and resistor RB reduce the gain of the normalized uncompensated voltage according to the ratio of their magnitude and resistor RS reduces the full scale output voltage of the linearization circuit by the compensated percentage error at full scale.
  • the lost gain and full scale output voltage can be recovered by providing an additional amplifier coupled to the output of the linearization circuit.
  • the linearization circuit of the present invention can generate a linearized output voltage having precision of about 1% of the uncompensated error of the non-linear voltage input.
  • the linearization circuit which compensates for an S-shaped bow non-linearity includes resistor RS1 and resistor RS2.
  • the resistance values for resistors RS1 and RS2 are determined in the general manner described for the circuit of FIG. 2a.
  • the non-linear voltage input to the circuit is normalized from -1 volt to +1 volt, i.e., 2.00 volts full scale.
  • the value for resistor RA is selected to equal the value of resistor RB causing a one-volt drop across resistor RS1 and diode CR1 and resistor RS2 and diode CR2. Diode CR1 and diode CR2 will operate in the non-linear range.
  • resistor RS1 The value for resistor RS1 is determined which causes the maximum error over the normalized scale of 0 volts to +1 volt to be a minimum.
  • resistor RS2 the value of resistor RS2 is determined which causes the maximum error over the normalized scale of -1 volt to 0 volts to be a minimum.
  • the transducer system 100 includes a transducer element 102 of the type described above for providing a voltage output proportional to the parameter being measured.
  • the output of the transducer element 102 is connected to the input of first amplifier 104.
  • the output from amplifier 104 is coupled to the input of a second amplifier 106 through a linearization circuit according to the present invention. If the non-linear voltage ramp produced by transducer element 102 has a negative bow non-linearity, resistor RA is shunted by the series combination of resistor RS and diode CR1 and resistor RS' and diode CR1' are eliminated.
  • resistor RB is shunted by the series combination of resistor RS' and diode CR1' and resistor RS and diode CR1 are eliminated.
  • the diodes CR1 and CR1' are provided as the PN injunction of a standard semiconductor transistor.
  • the output from the second amplifier 106 is connected to a gauge indicator 108 which indicates the measured parameter.
  • transducer element 102 In operation, in response to the variable parameter being measured, transducer element 102 provides a non-linear voltage output which is normalized from 0 to 2 volts full scale by amplifier 104.
  • the normalized uncompensated output voltage from amplifier 104 is linearized by the linearization circuit to provide a linear voltage output in the manner described above.
  • the value of resistor RS or resistor RS' is determined in the manner described in the above illustrative examples.
  • the linearized voltage output is applied to amplifier 106.
  • the precise magnitude of the measured parameter is recorded by guage indicator 108 which may be included in an instrumentation or control system.

Landscapes

  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • General Physics & Mathematics (AREA)
  • Indication And Recording Devices For Special Purposes And Tariff Metering Devices (AREA)
  • Measuring Instrument Details And Bridges, And Automatic Balancing Devices (AREA)

Abstract

Un circuit de linearisation (100) recoit un signal d'entree non lineaire et fournit un signal de compensation. La quantite de compensation non lineaire est predeterminee pour produire un signal de sortie lineaire. Dans une application particuliere, le circuit de linearisation (100) est utilise avec un transducteur a pression (102) pour compenser la sortie non lineaire produite par de tels transducteurs.
EP19820900241 1980-12-08 1981-12-04 Circuit de linearisation Withdrawn EP0065572A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US21432780A 1980-12-08 1980-12-08
US214327 2002-08-08

Publications (1)

Publication Number Publication Date
EP0065572A1 true EP0065572A1 (fr) 1982-12-01

Family

ID=22798649

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19820900241 Withdrawn EP0065572A1 (fr) 1980-12-08 1981-12-04 Circuit de linearisation

Country Status (3)

Country Link
EP (1) EP0065572A1 (fr)
JP (1) JPS57501891A (fr)
WO (1) WO1982002095A1 (fr)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3535252A1 (de) * 1985-10-03 1987-04-09 Vdo Schindling Schaltungsanordnung zur ansteuerung eines drehmagnetmessgeraets

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3041535A (en) * 1959-01-12 1962-06-26 Hewlett Packard Co Electrical measuring instrument
US3226633A (en) * 1960-06-08 1965-12-28 Schlumberger Well Surv Corp Induction logging apparatus including non-linear means for translating a detected signal
US3268813A (en) * 1962-03-22 1966-08-23 American Mach & Foundry Meter circuits with multiple increments of different slopes
DE1466677A1 (de) * 1965-07-17 1969-01-16 Deutsche Bundespost Schaltungsanordnung zur Linearisierung der Kennlinien von Gleichrichtern,insbesondere Messgleichrichtern
NL7608559A (nl) * 1976-08-02 1978-02-06 Philips Nv Draaispoelinstrument met lineaire karakteris- tiek.

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO8202095A1 *

Also Published As

Publication number Publication date
WO1982002095A1 (fr) 1982-06-24
JPS57501891A (fr) 1982-10-21

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PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

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Effective date: 19820728

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Withdrawal date: 19831024

RIN1 Information on inventor provided before grant (corrected)

Inventor name: DURKIN, JOSEPH J.