Automated system for low loss dielectric measurements under pressureM. Farzaneh and P. Destruel Citation: Review of Scientific Instruments 51, 1433 (1980); doi: 10.1063/1.1136098 View online: http://dx.doi.org/10.1063/1.1136098 View Table of Contents: http://scitation.aip.org/content/aip/journal/rsi/51/10?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Measurement of diffracted pressure fields using an automated measurement system. J. Acoust. Soc. Am. 124, 2517 (2008); 10.1121/1.4782937 Construction of a low-temperature thermodynamic measurement system for single crystal of molecularcompounds under pressures Rev. Sci. Instrum. 79, 053901 (2008); 10.1063/1.2912816 An automated Langmuir trough for systematic low surface pressure measurements Rev. Sci. Instrum. 61, 2640 (1990); 10.1063/1.1141852 Automated system for measurements of gas volume changes at constant pressure Rev. Sci. Instrum. 46, 726 (1975); 10.1063/1.1134297 Microwave Measurements of the Loss in Low Loss Dielectrics Rev. Sci. Instrum. 41, 820 (1970); 10.1063/1.1684656

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10

8

6

1? 4

X 2

~ 0 0;

~ -2 tIl , -E -4 ., > w

4

2

o

-2

-4

(a)

Running Time 22.84 hrs.

N = 1.66 X lOB

Baseline = 1.00 X 106

Timebase =3/Ls /channel Count Rate = 2022 counts/sec.

20 40 60 80

Channel Number

100 120

FIG. 2. (a) Afterpulsing as observed using a 3 JLs/channel timebase, and (b) corrected using a previously obtained aCT; tJ.T) determined at 1 JLs/channel.

and, therefore, . 11 .If

aCT; M t::.. T) = (1/ M) I I a(tj - (;; t::..T). (8) ;=1 j=1

The efficacy of the procedure is demonstrated in Fig. 2. Figure 2(a) shows the results of an afterpulsing measurement taken with a time base of 3 ILs/channel and

a count rate of2022 counts/so Figure 2(b) shows the same data corrected for the afterpulsing using a calibration taken at 1 ILs/channei.

The calibration and correction of afterpulsing effects can be employed to improve the precision of measure­ments using photon correlation spectroscopy, as shown elsewhere. 3 •6 The procedure removes the leading after­pulsing effect proportional to a( T; t::.. T). It does not cor­rect for the effects proportional to convolutions of a( T; t::.. T) and correlated light sources. Similar results may be obtained by splitting the incoming light between two photomultipliers and cross-correlating the outputs of the tubes. Though the latter technique frees one from relying upon a specific calibration, and may be used in very high precision experiments,7 it does reduce the effective counting rate. Everything else being equal, it quadruples the time required to make a measurement. Thus, the calibration procedure described will, in most cases, prove more practical.

The author is indebted to C. O. Alley for the use of some of his laboratory facilities, and to J. V. Sengers, E. A. Clerke, R. F. Chang, and R. W. Gammon for many interesting discussions. The research was sup­ported by National Science Foundation Grant DMR 79-10819.

1 C. J. Oliver in Photon Correlation and Light Beating Spectroscopy, edited by H. Z. Cummins and E. R. Pike (Plenum, New York, 1974).

, P. B. Coates, J. Phys. D, Appl. Phys. 6, 1159 (1973) . " L. Mandel and E. Wolf. Revs. Mod. Phys. 37, 231 (1965). 'E. Gulari and B. Chu, Rev. Sci. Instrum. 48,1560 (1977). :0 H. C. Burstyn, Ph.D. Dissertation, Univ. of Md. (1979). "H. C. Burstyn, J. V. Sengers, and P. Esfandiari, Phys. Rev. A

22, 282 (1980). 7 H. C. Burstyn. R. F. Chang, and J. V. Sengers, Phys. Rev. Lett.

44,410 (1980).

Automated system for low loss dielectric measurements under pressure

M. Farzaneh and P. Oestruel

Laboratoire de Genie Electrique associe au C. N. R. S .. Equipe "Materiaux Dielectriques': 2 rue Camichel. 31000 Toulouse. France

(Received 3 March 1980; accepted for publication 20 May 1980)

We describe here an automated system for dielectric measurements under pressure at high frequency. This system is governed by a Commodore micro-computer type P.E.T. 2001. The advantage of this equipment is to prevent any error due to operators in the measurement procedure and consequently to increase the accuracy of measurement.

PACS numbers: 06.30.Lz, 07.50. + f, 07.35. + k

We have presented in (our first paper)! an experimen­tal apparatus for the low-loss dielectric measurements under pressure. This short note describes how some of the difficulties of the manual operation have been suc­cessfully solved by automating all the sequences such as

the motors switching for positioning the sample and the upper electrode. For this purpose, some authors2 have presented an automated dielectric measurement system at the atmospheric pressure. However, some sequences of this system such as sample and electrode positioning

1433 Rev. Sci. Instrum. 51(10), Oct. 1980 0034-6748/80/101433-03$00.60 © 1980 American Institute of Physics 1433

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remain manual. Consequently, it cannot be used for the dielectric loss measurement under pressure.

Here, we mention briefly the principle of the measure­ments. It is about a high pressure bomb in which is placed a sample holder General Radio type 1690. The pressure in the bomb is obtained by means of a two-stage diaphragm compressor. The maximum gas pressure is 1500 bar in the chamber and the temperature of the sample is obtained and controlled from - 20°C to + 50 °C with a stability of less than 0.1 °C by the circulation of a fluid around the electrodes. A group of three dc driving motors Faulhaber type 03.2 K allows all the necessary operations such as sample positioning between the elec­trodes and finding the electrical resonance by displace­ment of the upper electrode. The measurements of the losses are based on the Q meter method3

-:' and with our po~sibilities, the losses are measured in the range of 100 kHz to 15 M Hz, that is to say we have to measure simul­taneously quality factor (Q) of the resonant circuit delivered by a precise voltmeter and the electrodes sepa­ration (d) provided by another precise voltmeter. For a measurement, this operation repeats itself two times, first with the sample between the electrodes ( Q 1, d 1) and then without the sample (Qz, dt). TH~ separation of elec­trodes is converted to an electrical voltage (D) by a 10 turns linear potentiometer which is coupled mechanically with the upper electrode. The problem is the measurement of Q and simultaneously the determination of D. Up to now, the problem is resolved by reducing the motor velocity which controls the movable electrode and searching the maximum value of Q and the correspond­ing D. This manner is not easy and it is tedious for the operator when he has to repeat the procedure many times (50 to 100 times per day). Moreover, every meas­urement of (Qh dlo Q~. d z) requires 1 I switchings for ordering the motors which can present some errors to the manipulation of these alternating sequences.

FIG. I. C: Micro·computer type P.E.T. 2001: B: Bus I.E.E.E. 488; R: Relay actuator Hewlett Packard type 59501 A: M,: dc motor for moving the electrode; M,: dc motor for positioning the sample: S: Sample holder General Radio type 1690 A; V: Voltmeter RACAL DANA Iype 6000; P: Linear potentiometer; Q: Q-meter Hewlett Packard type 43 42 A. A special clip system holds the sample between the electrodes and the sequences executed by the micro-computer for a given frequency. pressure and temperature are the following: (I) Leaving the sample between the electrodes and drawing back the pliers with the aid of the motor M" (2) Raising the upper electrode to leave an air gap over the sample (by M,). (3). (3') Finding the electrical resonance and corresponding electrodes separation with the sample (Q" d , ) by lowering the upper electrode. The operation stops itself when the upper electrode touches the sample. (4) Forwarding the pliers to hold the sample. (5) Raising the upper electrode. (6) Draw­ing out the sample. (7). (7') Finding the electrical resonance and cor­responding electrodes separation without the sample (Q,. d,) and stopping the sequence. (8). (9). (10) Raising the upper electrode. for­warding the sample and lowering the upper electrode to obtain the initial condition. After these sequences the computer displays the results such as (Q" d ,• Q,. d,). tan,). €. edge capacitance and the dis­persion factor. These sequences are repeated as many times as demanded.

For resolving these problems, the experimental ap­paratus is automated (Fig. l) by using a voltmeter RACAL DAN A type 6000 with two inputs and a logic output IEEE 488 which can deliver up to 40 measurements per second. All the necessary switchings for ordering the motors are possible with a programable relay actua-

TABLIc I. Comparison of data obtained by manual and automatic operation.

Data

The duration of a measurement of (Q" d , . Q,. d,)

The number of readings of Q per second

Accuracy of tanll for example for a low density polyethylene

Accuracy of € for example for a low density polyethylene

Manual System

12 mn

2

tan,) = (110 ± 5) x F= 12 MHz p= I bar T= +4OC tanll = (197 ± 8) x F= 12 MHz P = 950 bar T= +4°C

€ = 2.27 ± 0.01 p= I bar T= +4°C

€ = 2.33 ± 0.01 P = 950 bar T= +4°C

1434 Rev. Sci. Instrum., Vol. 51, No. 10, October 1980

10 ,;

10-1>

Automated System

10 mn

12

tan/) = (108 ± 2) x 10 ,; F= 12 MHz p= I bar T= +4°C tan,) = (195 ± 4) x 10- ,;

F= 12 MHz P = 950 bar 7 = +4°C

€ = 2.276 ± 0.005 P = I bar T= +4°C

€ = 2.327 ± 0.006 p = 950 bar T = +4°C

Notes

Remarks

Reduce of the measurement dura­tion

Better determination of the maxi­mum of Q. therefore more pre­cision

Better reproducibility for the val­ues determined

Better determination of the varia­tion of €

1434

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tor H.P. type 59501 A with a delay time of 50 ms. For the following reasons, we have chosen a micro-com­puter type P.E.T. 2001:

Interface IEEE 488 allowing to use multiple periph­erals;

8K bytes RAM; Cathode Ray Tube display permlttlOg to observe

schematically the different sequences of the measure­ments;

Low price in comparing with the other equivalent computers.

Furthermore, it computes directly the dissipation fac­tor, tana, permittivity E and the edge capacitance, as a function of frequency F, pressure P and temperature T and at the same time, it determines the dispersion factor over the measurements. This factor gives us the ac­curacy of the measurements. Additional advantages come from the increasing speed of the measurement of Q (12 measurements per second instead of 1 by the manual system) which gives better accuracies than does the manual's. This system produces a more rapid feed-back

1435 Rev. Sci. Instrum., Vol. 51, No. 10, October 1980

of information in a continuous monitoring programme. The experiments are more reproducible and they reduce considerable demands upon the operator.

We have presented the bloc diagram in the attached figure and compared some of the data between the manual and the automatized operations in Table I.

We can conclude that this automated system gives much more reproducible measurement with better ac­curacy than 3% for tan a and 0.3% for E and furthermore it is easier to execute the sequences and to compute values required.

We are grateful to the Centre National d'Etudes des Telecommunications for its financial aid.

I Bui Ai. D. Lebarbier, Hoang The Giam, J. C. Bapt, and M. Farzaneh, Rev. Sci. Instrum. 50, 625 (1979).

2 G. J. Hill, Conference Record of 1978 I.E.E.E. International Symposium on Electrical Insulation, I.E.E.E. 78 CH 1287.

"L. Hartshorn and W. H. Ward, J. Inc\. Elic. Eng. 79,597 (1936). 'W. Redish and K. A. Buckingham, Proc. I.E.E. 118, 255 (1971). , ASTM D 150-70, Standard methods of test for ac loss characteristics

and dielectric constant of solid electrical insulating materials.

Notes 1435

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