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Computer controlled measuring system for ring specimen
Journal of Magnetism and Magnetic Materials 19 (1980) 235-239 © North-Holland Publishing Company
COMPUTER CONTROLLED MEASURING SYSTEM FOR RING SPECIMEN Bengt MYRGREN Telefonaktiebolaget LM. Ericsson, Stockholm, Sweden
A magnetic measuring system for ring specimens has been constructed. An analysis of the use of the older reports with curves was made. Commonly, only remanence, coercivity, gmax and a quick and clear report was wanted. The new system is computcr controlled which needs little human intervention from sample preparation to report.
1. Short history
has to be reduced or a new laboratory worker employed. (6) The rings, standardized years ago, and the ring permeameters should not be changed. To these points were a few added when the system work started. (7) The overall accuracy should be equal or better than in the old equipment. (8) The detailed result should be stored for some months. (9) On special demand it must be possible to plot a curve. (10) In the report a distinct remark must be made for specimens and quantities outside specification. (11) The system should also be planned for other magnetic measurements.
Magnetic dc parameters, remanence, coercivity and maximum permeability were earlier measured by commutation and point-by-point methods. These measurements were not always reproducible from one laboratory to another depending on the apparatus, which gave different commutation time and losses. Some of the fluxmeters used gave different deflection for the same flux difference, but varying rate of flux change. By recording the curves with electronic integrators and XY-recorders the flux could be changed so slowly that the results from different laboratories agreed. The recorded curve showed that it was very difficult to demagnetize the rings.
2. Reasons for a new magnetic measuring system
3. Determination of the system
After many thousand curves on an XY-recorder the laboratory capacity was so strained that an analysis for the future had to be made. This analysis showed the following points. (1) Curves are of very little interest for most orderers. They want Br, Hc and/lmax. (2) Results should be presented in SI units. (3) The report should be given in a standard form for quick and easy reading. (4) Measuring time could be shortened by automatic regulation of the field. (5) The total production time for registration and preparation of samples, measuring and reporting
The demand for calculations, storage and reporting pointed out a need for a computer system with a mass storage device and a typewriter with a plotting mode. The measuring device should then work digitally if possible. As the quantities to be measured are analogue, the conversion to digital signals should occur as near the specimen as possible. The field could be measured as voltage over a resistor in the current path, with an A/D converter. The flux change gives a voltage in the measuring coil which can be measured by a voltage to frequency 235
236
B. Myrgren / Measuring system for ring specimen
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B. Myrgren /Measuring system for ring specimen
TELEFON AB LM ERICSSON MATERIALLABORATORIET
DATA FOR SOFTMAGNETIC MATERIALS
1(1)
Mark
BED
Prepared
Mel
Date
79-07-06
Document M 2598
Approved
MelC
Account no
272550/212
Work no
Ordering department TN/Omm
Information copy MeC,~Mp SB Material Dimension Manufacturer
Prcj nr
Relay iron 3047 2.5 mm "Relay Iron Co"
Heat treatment 800 C - 2h - N2 Number of anealed details Ring: 48 pieces 34/24 Information P/N 181/79
Charge: Ex 790516
RESULTS OF INVESTIGATION Marking
Length mm
447 E-I 447 E-2 *447 I-I 447 I-2 448 E-I 448 E-2 448 I-I 448 I-2 449 E-I 449 E-2 *449 I-I *449 I-2 450 E-I *450 E-2 *450 I-I e450 I-2 "451E-I '451E-2 451 I-I 451 I-2 *452 E-I *452 E-2 452 1-I 452 I-2
9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11
Area mm 2
umax
24.53 24.61 24.82 24.82 24.48 24.58 24.51 24.51 24.50 24.45 24.92 25.01 24.49 24.49 24.85 24.95 24.53 24.49 24.55 24.55 24.49 24.49 24.30 24.57
4700 4600 3900* 4000
4800 4800 4500 4500 4500 4600 3900* 3700* 4800 4800 3900* 3700* 4800 4900 4800 '4700 4300 4200 4700 4500
Br
HC
T
A/m
.86 .85 .89 .89 .85 .85 .86 .86 .87 .86 .97 1.03 .85 .84e 1.00 1.02 .84* .83 .86 .85 .84* .84* .87 .85
69 69 85 85 65 66 72 71 72 71 91 100 66 67 95 98 66 67 69 69 75 79 71 71
LME:s requirements for material 3047 Minimum Maximum
4000
.85 100.0
Summary LME:s requirements for material 3047 are not fullfilled for specimens and quantities marked with an asterisk
Fig. 2. Test report.
Mel 3594
238
B. Myrgren /Measuring system Cbrring specimen
converter. The control of the field change is most distinct in analogue form. Limits and current change directions and rate are set by D/A converters. The block diagram (fig. 1) shows the measuring system.
4. Realization All parts which were commercially available have been bought. The A/D converter should have a wide dynamic range. The maximal field strength must be measured and coercivity determined with better than 1% uncertainty without any changes in the measuring circuit. The A/D converter used has 16 bit resolution and l 0 gs conversion time including sampling time. The power amplifier for +8 V, +-45 A is programmable with a voltage o f +.10 V. It is fast enough to be driven with a 10 kHz sine wave. The current is measured as a voltage over a resistor with 0.1000 f2 between the potential terminals. Both the measuring points are floating. As the A/D converter has one input terminal grounded there is a differential instrumentation amplifier between the measuring points and the A/D converter. 45 A gives 4.5 V over 0.1000 g2 and the A/D converter has +-10 V for 16 bits. The amplifier is consequently adjusted to a gain of 2. The integrator is fundamentally a voltage to frequency (V/f) converter. There were no commercial V/f converters with the sensitivity which was necessary. The rings have 1 5 - 2 5 mm 2 area, the winding was a b e r y l l i u m - c o p p e r spring with 40 turns, which was screwed on the ring, and the flux density for 45 A was about 1.8 T. With wanted 200 bits for the virgin curve, the resolution must be 5 pVs turns. (By using the undimensional "turn" in the resolution figure, there will be no confusion about used coils.) The integrator is built with chopper-stabilized, differential, operational amplifiers. The input can thereby get a high impedance and the calibration is free from influence by the coil resistance. Yhermo e.m.f, causes always drift in integrators. An internal compensation prevents the use o f the system if the drift is outside 1 bit (5/aVs turn) in 20 s. By making use of two parallel integrators the time window, when no flux is integrated, amounts to about
50 ns or for a full 30-s measuring cycle to less then
100/2s. To control the current change rate so that the flux change is linear versus time, tire voltage is sensed on the measuring winding, amplified and compared with a reference voltage. The difference is then amplified in a summing amplifier which controls the power amplitier. The reference voltage and the current limit for the part of the curve which is to be started, is set by tire computer according to preset variables in the computer program. The computer is a miniconrputer with 16 bit words. The primary memory is 32 kwords. An operative system can handle periferic units. The software is developed partly in assembler language and partly in FORTRAN. This was the only high level language suitable for calculation, which in this computer could be linked to the assembler routines. A double diskette unit, with 256 kbyte memory on each diskette, was used for development o f the software and for the work with the measurements. Most of the data space is used for current values organized in the order they are measured. The number of values times 5/IVs is the flux value. A special vector indicates where the flux change direction has been opposed. The information about work number, identification of samples and similar is also stored on the diskette. All information which must be given to the computer is asked for by a typewriter, a daisy wheel printer with plotting facilities, on which the requested data are written. The diskettes can be stored for a period and used again when the data is no longer needed.
5. System in use The measuring system has to be isolated from the computer to avoid disturbances. All I/0s have been provided with optocouplers. The measuring time is about 30 s. In lh about 20 ring specimens can be measured and reported. Unfortunately mechanical measurement of the area, isolation, screwing on and off tile spring winding took about 2 h for 20 rings. This part of the measurement had to be simplified. An electronic balance with BCD output gives a
B. Myrgren / Measuring system for ring specimen direct method to determine the area for relay iron. Still the spring winding took 1 rain on and 1 rain off. A new contact device with 40 turns was made and fitted in the ring permeameter. Weighing is made during a measuring cycle and the demagnetized specimen can be put into an isolating ring. When the measuring cycle is completed the printer shows unsymmetry and different check-figures and finally remanence, coercivity and/1max. If the unsymmetry is within 1% the new ring is fitted into the ring permeameter, the new identification number is given and the measuring cycle can start as soon as the integrator has checked and compensated its own drift. When all the rings in an ordered test are measured the report can be written. The standard report (see fig. 2) has all information stored on the diskette. In the program memory there are tables with requirements for every material number. The remanence, coercivity and maximum permeability are compared with the requirements and rings and quantities outside specification are marked with an asterisk.
239
Another use is even more interesting. On behalf of the rapid function it is possible to study relay flux under operation and other functions up to 10 kHz (0.1 ms). The only limitation is that the sensitivity is poor for small relays where no room is left for a winding. For very high flux values the limit is set only by the maximum frequency in the integrator. Over 10 kHz the integrating error rises and for 100 kHz the error is about 1%. The memory cannot store more than about 8000 values but it is possible to store every tenth or every hundredth value. The same equipment can be used for measurements on permanent magnets if only a Hall generator is applied and the A/D converter measures the Hall voltage. This can be calibrated in field by a NMR device and the corrections made either from a table of values in the memory or by a mathematically fitted curve. Most of this is already tested and reported by Capptuller in PTB Braunschweig.
7. Summary 6. Possibilities in the future The standard test and the standard report save much time. Unfortunately the direct sensitivity and reproducibility are not good enough for an aging test since the reproducability error there should be about 0.2%. Some experiments have shown 0.5% with a slightly changed measuring cycle and there are no theoretical obstacles for better results.
A measuring system for a soft magnetic ring specimen was made, tested and refined to give quick and accurate measurements. Special care has been taken to give an easily readable report. The integrator construction, the system planning, the workmanship and the programming was made by Stefan Edstrgm at the Materials department of Telefonaktiebolaget L.M. Ericsson, Stockholm.
COMPUTER CONTROLLED MEASURING SYSTEM FOR RING SPECIMEN Bengt MYRGREN Telefonaktiebolaget LM. Ericsson, Stockholm, Sweden
A magnetic measuring system for ring specimens has been constructed. An analysis of the use of the older reports with curves was made. Commonly, only remanence, coercivity, gmax and a quick and clear report was wanted. The new system is computcr controlled which needs little human intervention from sample preparation to report.
1. Short history
has to be reduced or a new laboratory worker employed. (6) The rings, standardized years ago, and the ring permeameters should not be changed. To these points were a few added when the system work started. (7) The overall accuracy should be equal or better than in the old equipment. (8) The detailed result should be stored for some months. (9) On special demand it must be possible to plot a curve. (10) In the report a distinct remark must be made for specimens and quantities outside specification. (11) The system should also be planned for other magnetic measurements.
Magnetic dc parameters, remanence, coercivity and maximum permeability were earlier measured by commutation and point-by-point methods. These measurements were not always reproducible from one laboratory to another depending on the apparatus, which gave different commutation time and losses. Some of the fluxmeters used gave different deflection for the same flux difference, but varying rate of flux change. By recording the curves with electronic integrators and XY-recorders the flux could be changed so slowly that the results from different laboratories agreed. The recorded curve showed that it was very difficult to demagnetize the rings.
2. Reasons for a new magnetic measuring system
3. Determination of the system
After many thousand curves on an XY-recorder the laboratory capacity was so strained that an analysis for the future had to be made. This analysis showed the following points. (1) Curves are of very little interest for most orderers. They want Br, Hc and/lmax. (2) Results should be presented in SI units. (3) The report should be given in a standard form for quick and easy reading. (4) Measuring time could be shortened by automatic regulation of the field. (5) The total production time for registration and preparation of samples, measuring and reporting
The demand for calculations, storage and reporting pointed out a need for a computer system with a mass storage device and a typewriter with a plotting mode. The measuring device should then work digitally if possible. As the quantities to be measured are analogue, the conversion to digital signals should occur as near the specimen as possible. The field could be measured as voltage over a resistor in the current path, with an A/D converter. The flux change gives a voltage in the measuring coil which can be measured by a voltage to frequency 235
236
B. Myrgren / Measuring system for ring specimen
8 o
~o
.o
~ o
~j
0.-I
i &
m
I
a e~
g
8
s
~
m
/
c
.,-~
~8 0"4
I
o
C
C 0
.!
~o. ~o
o
C'~ ""~ B
ea co
B. Myrgren /Measuring system for ring specimen
TELEFON AB LM ERICSSON MATERIALLABORATORIET
DATA FOR SOFTMAGNETIC MATERIALS
1(1)
Mark
BED
Prepared
Mel
Date
79-07-06
Document M 2598
Approved
MelC
Account no
272550/212
Work no
Ordering department TN/Omm
Information copy MeC,~Mp SB Material Dimension Manufacturer
Prcj nr
Relay iron 3047 2.5 mm "Relay Iron Co"
Heat treatment 800 C - 2h - N2 Number of anealed details Ring: 48 pieces 34/24 Information P/N 181/79
Charge: Ex 790516
RESULTS OF INVESTIGATION Marking
Length mm
447 E-I 447 E-2 *447 I-I 447 I-2 448 E-I 448 E-2 448 I-I 448 I-2 449 E-I 449 E-2 *449 I-I *449 I-2 450 E-I *450 E-2 *450 I-I e450 I-2 "451E-I '451E-2 451 I-I 451 I-2 *452 E-I *452 E-2 452 1-I 452 I-2
9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11 9.11
Area mm 2
umax
24.53 24.61 24.82 24.82 24.48 24.58 24.51 24.51 24.50 24.45 24.92 25.01 24.49 24.49 24.85 24.95 24.53 24.49 24.55 24.55 24.49 24.49 24.30 24.57
4700 4600 3900* 4000
4800 4800 4500 4500 4500 4600 3900* 3700* 4800 4800 3900* 3700* 4800 4900 4800 '4700 4300 4200 4700 4500
Br
HC
T
A/m
.86 .85 .89 .89 .85 .85 .86 .86 .87 .86 .97 1.03 .85 .84e 1.00 1.02 .84* .83 .86 .85 .84* .84* .87 .85
69 69 85 85 65 66 72 71 72 71 91 100 66 67 95 98 66 67 69 69 75 79 71 71
LME:s requirements for material 3047 Minimum Maximum
4000
.85 100.0
Summary LME:s requirements for material 3047 are not fullfilled for specimens and quantities marked with an asterisk
Fig. 2. Test report.
Mel 3594
238
B. Myrgren /Measuring system Cbrring specimen
converter. The control of the field change is most distinct in analogue form. Limits and current change directions and rate are set by D/A converters. The block diagram (fig. 1) shows the measuring system.
4. Realization All parts which were commercially available have been bought. The A/D converter should have a wide dynamic range. The maximal field strength must be measured and coercivity determined with better than 1% uncertainty without any changes in the measuring circuit. The A/D converter used has 16 bit resolution and l 0 gs conversion time including sampling time. The power amplifier for +8 V, +-45 A is programmable with a voltage o f +.10 V. It is fast enough to be driven with a 10 kHz sine wave. The current is measured as a voltage over a resistor with 0.1000 f2 between the potential terminals. Both the measuring points are floating. As the A/D converter has one input terminal grounded there is a differential instrumentation amplifier between the measuring points and the A/D converter. 45 A gives 4.5 V over 0.1000 g2 and the A/D converter has +-10 V for 16 bits. The amplifier is consequently adjusted to a gain of 2. The integrator is fundamentally a voltage to frequency (V/f) converter. There were no commercial V/f converters with the sensitivity which was necessary. The rings have 1 5 - 2 5 mm 2 area, the winding was a b e r y l l i u m - c o p p e r spring with 40 turns, which was screwed on the ring, and the flux density for 45 A was about 1.8 T. With wanted 200 bits for the virgin curve, the resolution must be 5 pVs turns. (By using the undimensional "turn" in the resolution figure, there will be no confusion about used coils.) The integrator is built with chopper-stabilized, differential, operational amplifiers. The input can thereby get a high impedance and the calibration is free from influence by the coil resistance. Yhermo e.m.f, causes always drift in integrators. An internal compensation prevents the use o f the system if the drift is outside 1 bit (5/aVs turn) in 20 s. By making use of two parallel integrators the time window, when no flux is integrated, amounts to about
50 ns or for a full 30-s measuring cycle to less then
100/2s. To control the current change rate so that the flux change is linear versus time, tire voltage is sensed on the measuring winding, amplified and compared with a reference voltage. The difference is then amplified in a summing amplifier which controls the power amplitier. The reference voltage and the current limit for the part of the curve which is to be started, is set by tire computer according to preset variables in the computer program. The computer is a miniconrputer with 16 bit words. The primary memory is 32 kwords. An operative system can handle periferic units. The software is developed partly in assembler language and partly in FORTRAN. This was the only high level language suitable for calculation, which in this computer could be linked to the assembler routines. A double diskette unit, with 256 kbyte memory on each diskette, was used for development o f the software and for the work with the measurements. Most of the data space is used for current values organized in the order they are measured. The number of values times 5/IVs is the flux value. A special vector indicates where the flux change direction has been opposed. The information about work number, identification of samples and similar is also stored on the diskette. All information which must be given to the computer is asked for by a typewriter, a daisy wheel printer with plotting facilities, on which the requested data are written. The diskettes can be stored for a period and used again when the data is no longer needed.
5. System in use The measuring system has to be isolated from the computer to avoid disturbances. All I/0s have been provided with optocouplers. The measuring time is about 30 s. In lh about 20 ring specimens can be measured and reported. Unfortunately mechanical measurement of the area, isolation, screwing on and off tile spring winding took about 2 h for 20 rings. This part of the measurement had to be simplified. An electronic balance with BCD output gives a
B. Myrgren / Measuring system for ring specimen direct method to determine the area for relay iron. Still the spring winding took 1 rain on and 1 rain off. A new contact device with 40 turns was made and fitted in the ring permeameter. Weighing is made during a measuring cycle and the demagnetized specimen can be put into an isolating ring. When the measuring cycle is completed the printer shows unsymmetry and different check-figures and finally remanence, coercivity and/1max. If the unsymmetry is within 1% the new ring is fitted into the ring permeameter, the new identification number is given and the measuring cycle can start as soon as the integrator has checked and compensated its own drift. When all the rings in an ordered test are measured the report can be written. The standard report (see fig. 2) has all information stored on the diskette. In the program memory there are tables with requirements for every material number. The remanence, coercivity and maximum permeability are compared with the requirements and rings and quantities outside specification are marked with an asterisk.
239
Another use is even more interesting. On behalf of the rapid function it is possible to study relay flux under operation and other functions up to 10 kHz (0.1 ms). The only limitation is that the sensitivity is poor for small relays where no room is left for a winding. For very high flux values the limit is set only by the maximum frequency in the integrator. Over 10 kHz the integrating error rises and for 100 kHz the error is about 1%. The memory cannot store more than about 8000 values but it is possible to store every tenth or every hundredth value. The same equipment can be used for measurements on permanent magnets if only a Hall generator is applied and the A/D converter measures the Hall voltage. This can be calibrated in field by a NMR device and the corrections made either from a table of values in the memory or by a mathematically fitted curve. Most of this is already tested and reported by Capptuller in PTB Braunschweig.
7. Summary 6. Possibilities in the future The standard test and the standard report save much time. Unfortunately the direct sensitivity and reproducibility are not good enough for an aging test since the reproducability error there should be about 0.2%. Some experiments have shown 0.5% with a slightly changed measuring cycle and there are no theoretical obstacles for better results.
A measuring system for a soft magnetic ring specimen was made, tested and refined to give quick and accurate measurements. Special care has been taken to give an easily readable report. The integrator construction, the system planning, the workmanship and the programming was made by Stefan Edstrgm at the Materials department of Telefonaktiebolaget L.M. Ericsson, Stockholm.