GB1578441A - Thickness measuring gauge with reading hold facility - Google Patents

Thickness measuring gauge with reading hold facility Download PDF

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Publication number
GB1578441A
GB1578441A GB507176A GB507176A GB1578441A GB 1578441 A GB1578441 A GB 1578441A GB 507176 A GB507176 A GB 507176A GB 507176 A GB507176 A GB 507176A GB 1578441 A GB1578441 A GB 1578441A
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GB
United Kingdom
Prior art keywords
output
signal
thickness
amplifier
meter
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.)
Expired
Application number
GB507176A
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.)
Elcometer Instruments Ltd
Original Assignee
Elcometer Instruments Ltd
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 Elcometer Instruments Ltd filed Critical Elcometer Instruments Ltd
Priority to GB507176A priority Critical patent/GB1578441A/en
Priority to DE19772705624 priority patent/DE2705624A1/en
Publication of GB1578441A publication Critical patent/GB1578441A/en
Expired legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D7/00—Indicating measured values
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
    • G01B7/02—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness
    • G01B7/06—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness for measuring thickness
    • G01B7/10—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness for measuring thickness using magnetic means, e.g. by measuring change of reluctance
    • G01B7/105—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness for measuring thickness using magnetic means, e.g. by measuring change of reluctance for measuring thickness of coating
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D1/00—Measuring arrangements giving results other than momentary value of variable, of general application

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)
  • Length Measuring Devices With Unspecified Measuring Means (AREA)

Description

(54) A THICKNESS MEASURING GAUGE WITH READING HOLD FACILITY (71) We, ELCOMETIR INSTRUMENTS LIMITED, a British Company of Edge Lane, Droylsden, Manchester M35 6BU, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a thickness measuring instrument.
In an already known instrument, a probe is placed on the layer whose thickness is to be measured. A signal is fed from the probe to an accurate instrument which indicates the thickness of the layer and the signal is converted in the instrument into a thickness measurement which is represented on a meter. Instruments of this type are often repeatedly used when checking, for example, the thickness of an area of paint on the side of a ship. To check the area thoroughly, thousands of readings are necessary. When the probe is removed after each reading, the meter needle returns to the infinity position and, on making contact again with the probe at a different position, the needle moves again to record the new reading. The needle does not settle down immediately, however, but oscillates about the new position for some time.This constant movement of the meter needle can result in considerable strain on the operator quite apart from the inherent disadvantage of having to wait for the needle to settle down at each reading.
According to the present invention, there is provided a thickness measuring instrument for measuring the thickness of a coating on a substrate comprising a probe adapted to be placed on the coating, said probe including an excitation coil and a detection coil for producing an A.C. signal, means for receiving from the detection coil an A.C. signal representative of a coating thickness measured, means for converting the A.C. signal to a D.C. signal, means for displaying the D.C.
signal and means for maintaining the D.C.
signal in order to maintain the display at a measured value for a time sufficient to enable an operator to read the value after a measurement has been made irrespective of whether the probe is kept on the coating or not and until a further measurement can be made.
A preferred embodiment of the invention may include any one or more of the following features.
(a) The means for maintaining comprises a capacitor, (b) The means for maintaining comprises a switch, (c) The switch of (b) is connected to a timer, (d) The switch (b) is a Schmitt - trigger circuit, (e) The timer of (c) comprises a first monostable circuit, (f) The timer of (c) comprises a second monostable circuit, (g) The output of the second monostable circuit is arranged to control a sam pling switch connected between the output of the instrument and the capacitor of (a), (h) The means for displaying comprises a pointer, (i) The means for displaying comprises a digital read out, (j) The capacitor of (a) is connected to the means for displaying through an amplifier acting as a buffer.
In order that the invention may be more clearly understood, one embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a block circuit diagram of a thickness measuring gauge, Figure 2 shows a block circuit diagram of a hold device for use with the gauge of Figure 1, and Figure 3 shows operatiqnal waveforms at various points on the circuit of Figure 1.
Referring to Figure 1, the gauge comprises a probe 1 which houses an excitation coil 2 and a detection coil 3. The excitation coil 2 is connected to an oscillator 4 which has a feed back loop 5 to provide for control of the amplitude and stability of the oscillator. The detection coil 3 is connected to an A.C. amplifier 6 whose output is connected to a detector 7. The output of the detector 7 is connected to the input of a meter amplifier 8 whose output is connected to the meter mechanism 9 itself. A calibration control 10 is provided in parallel with the meter amplifier 8 and a set zero device 11 is connected to the input of the meter amplifier 8. The arrangement is supplied from a stabilised battery power supply indicated generally at 12.
.Referring to Figure 2, the basic gauge of Figure 1 excluding meter mechanism 9 is indicated diagrammatically at 20 with the probe at 1. The output of the meter amplifier 8 of gauge 20 is connected to a switch in 'the form of a Schmitt trigger circuit 21. The output of the trigger circuit 21 is connected to a timer in the form of a delay monostable circuit 22 and the output of this monostable circuit 22 is connected to the input of a further monostable 23. The output of the gaiig 20 is also connected through a sampling switch 24, bold amplifier 25 and two position switch 26 to the actual meter mechanism 9. A storage capacitor 27 is connected between the input of the hold amplifier and earth.The sampling switch 24 is controlled by the monostable 23 to the output of which the switch 24 is connected.
The operation of the arrangement will now be described in relation to the measure anent of the thickness of a non-magnetic coating 30 on a ferrous substrate 31.
The probe 1 is first placed on the uncoated ferrous substrate to set the meter zero position. The A.C. signal in the excitation coil 2 induces a signal electromagnetically in the detection coil 3. The strength of the induced signal is dependant on the magnetic reluctance of the path between the two coils. The induced signal is amplified in the A.C. amplifier 6 and then converted to a D.C. voltage in the detector 7. This D.C. voltage is then ;fed to the input of the meter amplifier 8 and the set zero control 11 is adjusted to give a zero reading on the gauge 9.
If the probe is now placed on the coated substrate, the magnetic reluctance of the magnetic path between the excitation and detection coils is increased because of the in tervening layer 30 of non-magnetic material.
The signal induced in the detection coil 3 is accordingly reduced, the D.C. voltage output from the detector 7 is reduced and an error signal is created at the input of the meter amplifier 8. As a result, the output from the meter amplifier 8 increases to produce a deflection on the gauge corresponding to the thickness of the coating 30. The calibration control 10 may be used to compensate for small changes in system gain. It may also be used to calibrate the instrument against standard thickness.
The above description is of the instrument operating in its "normal" mode, that is, without the hold facility. To use the gauge in the "hold" mode, the switch 26 is switched from the normal to the hold position. The output from the meter amplifier 8 is then fed to the Schmitt trigger 21 which produces a change in output level when the meter amplifier 8 output crosses a variable pre-set reference level (diagrammatically shown at 29). This is arranged to happen at a signal level for which the meter would normally read 120% full scale deflection. The abrupt change in signal level at the output of the trigger circuit 21 initiates the timing cycle of the delay monostable causing a delay of 300 milliseconds. The purpose of this time delay is to enable the signal level representing the coating thickness to settle to its final value after the probe has been placed on the coating surface.At the end of that timing cycle, the delay monostable reverts to its stable state and the ensuing signal at its output initiates a further timing cycle, this time controlled by the sample monostable 23. This monostable 23 produces at its output a constant width pulse of approximately 50 milliseconds duration which is used to close the normally open sampling switch 24 for that period of time.
When the sampling switch 24 is closed, the storage capacitor 27 is charged to the value reached by the output of the meter amplifier which corresponds to the thickness of the coating measured. At the end of the constant width pulse produced by the sample monostable 23, the switch 24 opens. The storage capacitor 27 retains its charge and the capacitor voltage is displayed on the gauge via the hold amplifier acting as a buffer stage. When the probe is removed from the coating material the meter indication stays the same until a different thickness is measured when the whole process is repeated and the gauge displays the new thickness.
The waveforms at various parts of the circuit are shown on Figure 3 for two thickness readings.
WHAT WE CLAIM IS:- 1. A thickness measuring instrument for measuring the thickness of a coating on a substrate comprising a probe adapted to be placed on the coating, said probe including an excitation coil and a detection coil for producing an A.C. signal, means for receiving from the detection coil an A.C. signal representative of a coating thickness measured, means for converting the A.C. signal to a D.C. signal, means for displaying the D.C.
signal and means for maintaining the D.C.
signal in order to maintain the display at
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (12)

**WARNING** start of CLMS field may overlap end of DESC **. has a feed back loop 5 to provide for control of the amplitude and stability of the oscillator. The detection coil 3 is connected to an A.C. amplifier 6 whose output is connected to a detector 7. The output of the detector 7 is connected to the input of a meter amplifier 8 whose output is connected to the meter mechanism 9 itself. A calibration control 10 is provided in parallel with the meter amplifier 8 and a set zero device 11 is connected to the input of the meter amplifier 8. The arrangement is supplied from a stabilised battery power supply indicated generally at 12. .Referring to Figure 2, the basic gauge of Figure 1 excluding meter mechanism 9 is indicated diagrammatically at 20 with the probe at 1. The output of the meter amplifier 8 of gauge 20 is connected to a switch in 'the form of a Schmitt trigger circuit 21. The output of the trigger circuit 21 is connected to a timer in the form of a delay monostable circuit 22 and the output of this monostable circuit 22 is connected to the input of a further monostable 23. The output of the gaiig 20 is also connected through a sampling switch 24, bold amplifier 25 and two position switch 26 to the actual meter mechanism 9. A storage capacitor 27 is connected between the input of the hold amplifier and earth.The sampling switch 24 is controlled by the monostable 23 to the output of which the switch 24 is connected. The operation of the arrangement will now be described in relation to the measure anent of the thickness of a non-magnetic coating 30 on a ferrous substrate 31. The probe 1 is first placed on the uncoated ferrous substrate to set the meter zero position. The A.C. signal in the excitation coil 2 induces a signal electromagnetically in the detection coil 3. The strength of the induced signal is dependant on the magnetic reluctance of the path between the two coils. The induced signal is amplified in the A.C. amplifier 6 and then converted to a D.C. voltage in the detector 7. This D.C. voltage is then ;fed to the input of the meter amplifier 8 and the set zero control 11 is adjusted to give a zero reading on the gauge 9. If the probe is now placed on the coated substrate, the magnetic reluctance of the magnetic path between the excitation and detection coils is increased because of the in tervening layer 30 of non-magnetic material. The signal induced in the detection coil 3 is accordingly reduced, the D.C. voltage output from the detector 7 is reduced and an error signal is created at the input of the meter amplifier 8. As a result, the output from the meter amplifier 8 increases to produce a deflection on the gauge corresponding to the thickness of the coating 30. The calibration control 10 may be used to compensate for small changes in system gain. It may also be used to calibrate the instrument against standard thickness. The above description is of the instrument operating in its "normal" mode, that is, without the hold facility. To use the gauge in the "hold" mode, the switch 26 is switched from the normal to the hold position. The output from the meter amplifier 8 is then fed to the Schmitt trigger 21 which produces a change in output level when the meter amplifier 8 output crosses a variable pre-set reference level (diagrammatically shown at 29). This is arranged to happen at a signal level for which the meter would normally read 120% full scale deflection. The abrupt change in signal level at the output of the trigger circuit 21 initiates the timing cycle of the delay monostable causing a delay of 300 milliseconds. The purpose of this time delay is to enable the signal level representing the coating thickness to settle to its final value after the probe has been placed on the coating surface.At the end of that timing cycle, the delay monostable reverts to its stable state and the ensuing signal at its output initiates a further timing cycle, this time controlled by the sample monostable 23. This monostable 23 produces at its output a constant width pulse of approximately 50 milliseconds duration which is used to close the normally open sampling switch 24 for that period of time. When the sampling switch 24 is closed, the storage capacitor 27 is charged to the value reached by the output of the meter amplifier which corresponds to the thickness of the coating measured. At the end of the constant width pulse produced by the sample monostable 23, the switch 24 opens. The storage capacitor 27 retains its charge and the capacitor voltage is displayed on the gauge via the hold amplifier acting as a buffer stage. When the probe is removed from the coating material the meter indication stays the same until a different thickness is measured when the whole process is repeated and the gauge displays the new thickness. The waveforms at various parts of the circuit are shown on Figure 3 for two thickness readings. WHAT WE CLAIM IS:-
1. A thickness measuring instrument for measuring the thickness of a coating on a substrate comprising a probe adapted to be placed on the coating, said probe including an excitation coil and a detection coil for producing an A.C. signal, means for receiving from the detection coil an A.C. signal representative of a coating thickness measured, means for converting the A.C. signal to a D.C. signal, means for displaying the D.C.
signal and means for maintaining the D.C.
signal in order to maintain the display at
a measured value for a time sufficient to enable an operator to read the value after a measurement has been made irrespective of whether the probe is kept on the coating or not and until a further measurement can be made.
2. A thickness measuring instrument as claimed in Claim 1, in which the means for maintaining comprises a capacitor.
3. A thickness measuring instrument as claimed in Claim 1 or 2, in which the means for maintaining comprises a switch.
4. A thickness measuring instrument as claimed in Claim 3, in which the switch is connected to a timer.
5. A thickness measuring instrument as claimed in Claim 3 or 4, in which the switch is a Schmitt trigger circuit.
6. A thickness measuring instrument as claimed in Claim 4, or Claim 5 when appendant to Claim 4, in which the timer comprises a first monostable circuit.
7. A thickness measuring instrument as claimed in Claim 6, in which the timer comprises a second monostable circuit.
8. A thickness measuring instrument as claimed in Claim 7, in which a sampling switch is connected between the output of the instrument and the capacitor and the output of the second monostable circuit is arranged to control this sampling switch.
9. A thickness measuring instrument as claimed in any preceding claim, in which the means for displaying comprises a pointer.
10. A thickness measuring instrument as claimed in any of Claims 1 to 8, in which the means for displaying comprises a digital readout.
11. A thickness measuring instrument as claimed in any of claims 2 to 7 or in Claim 9 or 10 when appendant to any claims 2 to 7, in which the capacitor is connected to the means for displaying through an amplifier acting as a buffer.
12. A thickness measuring instrument substantially as hereinbefore described with reference to Figs. 1, 2 and 3 of the accompanying drawings.
GB507176A 1976-02-10 1976-02-10 Thickness measuring gauge with reading hold facility Expired GB1578441A (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
GB507176A GB1578441A (en) 1976-02-10 1976-02-10 Thickness measuring gauge with reading hold facility
DE19772705624 DE2705624A1 (en) 1976-02-10 1977-02-10 MEASURING DEVICE

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB507176A GB1578441A (en) 1976-02-10 1976-02-10 Thickness measuring gauge with reading hold facility

Publications (1)

Publication Number Publication Date
GB1578441A true GB1578441A (en) 1980-11-05

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Family Applications (1)

Application Number Title Priority Date Filing Date
GB507176A Expired GB1578441A (en) 1976-02-10 1976-02-10 Thickness measuring gauge with reading hold facility

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DE (1) DE2705624A1 (en)
GB (1) GB1578441A (en)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0170341A1 (en) * 1984-07-31 1986-02-05 Kett Electric Laboratory Instrument for measuring film thickness
US4870359A (en) * 1986-06-18 1989-09-26 Ngk Insulators, Ltd. Method for measuring the thickness of a ceramic tubular molded body
GB2311615A (en) * 1996-03-20 1997-10-01 Peter Thomas Ormiston Measuring the thickness of a coating

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2811368A1 (en) * 1978-03-16 1979-09-27 Felix Von Rueling Measurement value indication method - displays sheet thicknesses using three LEDs showing three comparator states
FR2459448A1 (en) * 1979-06-18 1981-01-09 Indre Sa Forges Basse Rolled metal strip thickness fault detector - uses parallel amplifiers to measure crest and valley thickness signals

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0170341A1 (en) * 1984-07-31 1986-02-05 Kett Electric Laboratory Instrument for measuring film thickness
US4870359A (en) * 1986-06-18 1989-09-26 Ngk Insulators, Ltd. Method for measuring the thickness of a ceramic tubular molded body
GB2311615A (en) * 1996-03-20 1997-10-01 Peter Thomas Ormiston Measuring the thickness of a coating

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Publication number Publication date
DE2705624A1 (en) 1977-08-11

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PCNP Patent ceased through non-payment of renewal fee