17:
286:, or simply does not rest firmly against the flat surface, the distance between the part to be measured and the surface it is placed upon will be erroneously included in the thickness measurement. This error can be eliminated by using two capacitive sensors to measure a single part. Capacitive sensors are placed on either side of the part to be measured. By measuring the parts from both sides, curvature and deformities are taken into account in the
313:
While capacitive displacement sensors are most often used to sense changes in position of conductive targets, they can also be used to sense the thickness and/or density of non-conductive targets as well. A non-conductive object placed in between the probe and conductive target will have a different
223:
The operation of the sensor for measuring thickness of non-conductive materials can be thought of as two capacitors in series, with each having a different dielectric (and dielectric constant). The sum of the thicknesses of the two dielectric materials remains constant but the thickness of each can
322:
Capacitive displacement sensors are often used in metrology applications. In many cases, sensors are used “to measure shape errors in the part being produced. But they also can measure the errors arising in the equipment used to manufacture the part, a practice known as machine tool metrology”. In
372:
used by eddy current sensors This leads to a variety of differences between the two sensing technologies, with the most notable differences being that capacitive sensors are generally capable of higher resolution measurements, and eddy current sensors work in dirty environments while capacitive
277:
Capacitive displacement sensors can be used to make very precise thickness measurements. Capacitive displacement sensors operate by measuring changes in position. If the position of a reference part of known thickness is measured, other parts can be subsequently measured and the differences in
227:
A sensor for measuring fluid levels works as two capacitors in parallel with constant total area. Again the difference in the dielectric constant of the fluid and the dielectric constant of air results in detectable changes in the capacitance between the conductive probes or plates.
347:
Capacitive displacement sensors are often used in assembly line testing. Sometimes they are used to test assembled parts for uniformity, thickness or other design features. At other times, they are used to simply look for the presence or absence of a certain component, such as
224:
vary. The thickness of the material to be measured displaces the other dielectric. The gap is often an air gap, (dielectric constant = 1) and the material has a higher dielectric. As the material gets thicker, the capacitance increases and is sensed by the system.
314:
dielectric constant than the air in the gap and will therefore change the
Capacitance between probe and target. (See the first equation above) By analyzing this change in capacitance, the thickness and density of the non-conductor can be determined.
293:
The thickness of plastic materials can be measured with the material placed between two electrodes a set distance apart. These form a type of capacitor. The plastic when placed between the electrodes acts as a dielectric and displaces air (which has
73:
to two conductive objects with a gap between them. A simple demonstration is two parallel conductive plates of the same profile with a gap between them and a charge applied to them. In this situation, the
Capacitance can be expressed by the
278:
position can be used to determine the thickness of these parts. In order for this to be effective using a single probe, the parts must be completely flat and measured on a perfectly flat surface. If the part to be measured has any
265:. By knowing the exact runout of these spindles, disc drive manufacturers are able to determine the maximum amount of data that can be placed onto the drives. Capacitive sensors are also used to ensure that disc drive platters are
165:
There are two general types of capacitive displacement sensing systems. One type is used to measure thicknesses of conductive materials. The other type measures thicknesses of non conductive materials or the level of a fluid.
177:
of the material in the gap (usually air) also remains constant, "any change in capacitance is a result of a change in the distance between the probe and the target." Therefore, the equation above can be simplified to:
219:
Where α indicates a proportional relationship. Due to this proportional relationship, a capacitive sensing system is able to measure changes in capacitance and translate these changes in distance measurements.
129:
339:
spindles. By measuring errors in the machines themselves, rather than simply measuring errors in the final products, problems can be dealt with and fixed earlier in the manufacturing process.
27:
are "non-contact devices capable of high-resolution measurement of the position and/or change of position of any conductive target". They are also able to measure the thickness or density of
298:
of 1, different from the plastic). Consequently, the capacitance between the electrodes changes. The capacitance changes can then be measured and correlated with the material's thickness.
261:
In the disc drive industry, capacitive displacement sensors are used to measure the runout (a measure of how much the axis of rotation deviates from an ideal fixed line) of disc drive
214:
241:
One of the more common applications of capacitive sensors is for precision positioning. Capacitive displacement sensors can be used to measure the position of objects down to the
603:
663:
524:
169:
A capacitive sensing system for conductive materials uses a model similar to the one described above, but in place of one of the conductive plates, is the
634:
173:, and in place of the other, is the conductive target to be measured. Since the area of the probe and target remain constant, and the
352:. Using capacitive sensors to test assembly line parts can help to prevent quality concerns further along in the production process.
585:
503:
478:
688:
622:
323:
many cases, the sensors are used to analyze and optimize the rotation of spindles in various machine tools, examples include
16:
540:
84:
600:
301:
Capacitive sensors circuits can be constructed that are able to detect changes in capacitance on the order of a 10
143:
660:
521:
683:
552:
184:
522:
Capacitive Sensor
Operation and Optimization How Capacitive Sensors Work and How to Use Them Effectively
654:
295:
250:
151:
447:
451:
419:
31:
materials. Capacitive displacement sensors are used in a wide variety of applications including
581:
499:
474:
70:
468:
429:
414:
667:
625:, A comparison between capacitive and eddy current sensing technology from Lion Precision.
607:
528:
424:
332:
324:
262:
369:
365:
564:
Lawrence
Livermore National Laboratory: Engineering Precision into Laboratory Projects
249:
need to be positioned for exposure. Capacitive sensors are also used to pre-focus the
677:
246:
55:
47:
32:
28:
245:
level. This type of precise positioning is used in the semiconductor industry where
361:
40:
648:
336:
287:
66:
454:
266:
174:
36:
402:
395:
283:
279:
242:
51:
43:
566:, Examples of advances made by LLNL in the field of precision measurement.
531:, An in depth discussion of capacitive sensor theory from Lion Precision.
75:
563:
364:(or inductive) displacement sensors; however capacitive sensors use an
170:
328:
302:
15:
657:- Tutorial on Capacitive Sensors for Nanopositioning Applications
349:
290:
and their effects are not included in the thickness readings.
670:- How Capacitive Sensors Work and How to Use Them Effectively
360:
Capacitive displacement sensors share many similarities to
610:, A tutorial on using capacitive sensors for glue sensing.
69:
is an electrical property which is created by applying an
377:
Other non-displacement capacitive sensing applications
195:
187:
95:
87:
35:
processing, assembly of precision equipment such as
543:, A tutorial on capacitive thickness measurements.
208:
124:{\displaystyle C={\dfrac {\varepsilon _{0}KA}{d}}}
123:
623:Lion Precision Capacitive Eddy Current Comparison
635:Users Manual for Siemens Capacitive Sensors p.54
50:testing. These types of sensors can be found in
517:
515:
356:Comparison to eddy current displacement sensors
269:to the spindle before data is written to them.
651:- Patient Monitoring Using Capacitive Sensors
8:
618:
616:
253:used in testing and examining the wafers.
448:Lion Precision Capacitive Sensor Overview
194:
186:
102:
94:
86:
209:{\displaystyle C\propto {\dfrac {1}{d}}}
440:
498:. Worth Publishers. pp. 653–660.
655:Capacitive Sensors for Motion Control
382:Testing the moisture content of grain
7:
162:is the distance between the plates.
39:, precision thickness measurements,
14:
541:Capacitive Thickness Measurements
391:Detecting water content in fuels
273:Precision thickness measurements
158:is the area of the plates, and
25:Capacitive displacement sensors
394:Fuel composition sensors (for
1:
58:facilities around the world.
154:of the material in the gap,
20:Industrial capacitive sensor
578:Precision Spindle Metrology
705:
494:Paul Allen Tipler (1982).
470:Sensor Technology Handbook
144:permittivity of free space
661:Capacitive Sensor Theory
62:Basic capacitive theory
576:Eric R. Marsh (2009).
496:Physics Second Edition
473:. Newnes. p. 94.
467:Jon S. Wilson (2005).
318:Machine tool metrology
309:Non-conductive targets
210:
125:
21:
689:Measuring instruments
601:Sensing Glue on Paper
580:. Destech Pubns Inc.
343:Assembly line testing
237:Precision positioning
211:
138:is the capacitance, ε
126:
19:
649:Medical Engineering
553:Film thickness gauge
457:from Lion Precision.
251:electron microscopes
185:
85:
296:dielectric constant
257:Disc drive industry
152:dielectric constant
666:2015-12-02 at the
606:2010-07-09 at the
527:2015-12-02 at the
452:capacitive sensing
420:Capacitive sensing
368:as opposed to the
206:
204:
121:
119:
22:
450:, An overview of
305:(10 attofarads).
203:
118:
71:electrical charge
696:
684:Position sensors
637:
632:
626:
620:
611:
598:
592:
591:
573:
567:
561:
555:
550:
544:
538:
532:
519:
510:
509:
491:
485:
484:
464:
458:
445:
430:Inductive sensor
415:Proximity sensor
373:sensors do not.
333:milling machines
325:surface grinders
215:
213:
212:
207:
205:
196:
130:
128:
127:
122:
120:
114:
107:
106:
96:
704:
703:
699:
698:
697:
695:
694:
693:
674:
673:
668:Wayback Machine
645:
640:
633:
629:
621:
614:
608:Wayback Machine
599:
595:
588:
575:
574:
570:
562:
558:
551:
547:
539:
535:
529:Wayback Machine
520:
513:
506:
493:
492:
488:
481:
466:
465:
461:
446:
442:
438:
425:List of sensors
411:
379:
358:
345:
320:
311:
275:
259:
239:
234:
183:
182:
141:
98:
97:
83:
82:
64:
12:
11:
5:
702:
700:
692:
691:
686:
676:
675:
672:
671:
658:
652:
644:
643:External links
641:
639:
638:
627:
612:
593:
586:
568:
556:
545:
533:
511:
504:
486:
479:
459:
439:
437:
434:
433:
432:
427:
422:
417:
410:
407:
406:
405:
399:
392:
389:
386:
383:
378:
375:
370:magnetic field
366:electric field
357:
354:
344:
341:
319:
316:
310:
307:
274:
271:
258:
255:
247:silicon wafers
238:
235:
233:
230:
217:
216:
202:
199:
193:
190:
139:
132:
131:
117:
113:
110:
105:
101:
93:
90:
63:
60:
29:non-conductive
13:
10:
9:
6:
4:
3:
2:
701:
690:
687:
685:
682:
681:
679:
669:
665:
662:
659:
656:
653:
650:
647:
646:
642:
636:
631:
628:
624:
619:
617:
613:
609:
605:
602:
597:
594:
589:
587:1-60595-003-3
583:
579:
572:
569:
565:
560:
557:
554:
549:
546:
542:
537:
534:
530:
526:
523:
518:
516:
512:
507:
505:0-87901-135-1
501:
497:
490:
487:
482:
480:0-7506-7729-5
476:
472:
471:
463:
460:
456:
453:
449:
444:
441:
435:
431:
428:
426:
423:
421:
418:
416:
413:
412:
408:
404:
400:
397:
393:
390:
387:
385:Soil moisture
384:
381:
380:
376:
374:
371:
367:
363:
355:
353:
351:
342:
340:
338:
334:
330:
326:
317:
315:
308:
306:
304:
299:
297:
291:
289:
285:
281:
272:
270:
268:
264:
256:
254:
252:
248:
244:
236:
231:
229:
225:
221:
200:
197:
191:
188:
181:
180:
179:
176:
172:
167:
163:
161:
157:
153:
149:
145:
137:
115:
111:
108:
103:
99:
91:
88:
81:
80:
79:
77:
72:
68:
61:
59:
57:
56:manufacturing
53:
49:
48:assembly line
45:
42:
38:
34:
33:semiconductor
30:
26:
18:
630:
596:
577:
571:
559:
548:
536:
495:
489:
469:
462:
443:
362:eddy current
359:
346:
321:
312:
300:
292:
276:
260:
240:
232:Applications
226:
222:
218:
168:
164:
159:
155:
147:
135:
133:
65:
41:machine tool
24:
23:
401:Capacitive
337:air bearing
288:measurement
67:Capacitance
37:disk drives
678:Categories
455:technology
436:References
403:load cells
303:picofarads
267:orthogonal
175:dielectric
146:constant,
398:vehicles)
396:flex fuel
284:deformity
280:curvature
243:nanometer
192:∝
100:ε
52:machining
44:metrology
664:Archived
604:Archived
525:Archived
409:See also
388:Humidity
263:spindles
76:equation
150:is the
142:is the
584:
502:
477:
335:, and
329:lathes
171:sensor
134:Where
582:ISBN
500:ISBN
475:ISBN
350:glue
54:and
46:and
282:or
680::
615:^
514:^
331:,
327:,
78::
590:.
508:.
483:.
201:d
198:1
189:C
160:d
156:A
148:K
140:0
136:C
116:d
112:A
109:K
104:0
92:=
89:C
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
