6.1 Straight detection 6.2 Balanced detection 6.3 Calibrators 6.4 Interference 6.5 The choice between straight and balanced detection 6.6 Common mode rejectionChap. 6 Actual Detection Circuits

Straight detection

Straight detection1. : , 10-250kHz 80dB . .2. : discharge-free.3. : , .4. High-voltage rail : free, .5. a : , .6. k : discharge-free, , a k .7. Z : (shunt). Z 1:N , - . . 50-100kHz 500kHz .

Straight detection8.1:N : .9. (A) : Z . . 10kHz(mid-point 75kHz), 30kHz(mid-point 150kHz), 350kHz(mid-point 22kHz)10. . . picocoulomb meter picocoulomb peak voltmeter . picocoulomb meter 30 . X-Y recorder picocoulomb meter , .11. Faraday cage Faraday cage. cage . X-Y recorder , .

Straight detection6.1.2 Characteristics1. q . 5.25.3 n=a/k , v mV 1uF uV .2. ( noise noise ) (pC)

a C pF . ) 6.1

SampleStep-up ratioSensitivity(pC)100pF20.0110nF50.101uF451.00

Straight detection3. . . 20us 4 250 .

Straight detection6.1.3 Calibration

- (1,5,100pC) . pF . Calibrator . pC , , . , pC Y calibrate . Calibrator Calibration setting . No setting (0.1 , 10 , 100) . setting .

Straight detection6.1.4 Nonrecommended calibration 6.3-Calibration 6.3 . . calibrator . real discharge q calibration discharge qcal : ( )

(6.3)

Straight detection real discharge internal calibraion . capacitor , 100% . , , . . , . (1+(a/k) .

6 . 2 Balanced detection

Balanced detection6.2.1 priciples . main . Z1 Z2 balance . a a' a' a . balancing (6.5) . , .

Balanced detection6.2.2 Rejection ratio

(6.5 1) : 2 normal calibration . rejection ratio m . m= display / display (6.4)

calibration balancing , 1 balance , 2 calibrate , 1 . rejection ratio . . m = 5000 for two identical samples , well screed. m = 100 to 500 for two unequal samples but with the same insulating material m = 3 to 30 for a sample balanced against a coupling capacitor

Balanced detection6.2.3 Advantage of balanced detection balanced straight . . 1 . .2 . balance , , . straight .3 . balanced , .

6.2.4 Actual balanced circuit balanced , 6.6 . Zaengl Klauss . balanced .

Balanced detection

Balanced detection1 . straight . .2 . . 3 . -free . -free -free .4. k . , k , rejection ratio . .5 . a a' balanced . a a' . , gis . . . balanced .6 . R R' . R R a . R' , balance fine-turned . C . a a' R R' .

Balanced detection7 . S S' balanced . S switched over (1) a ,(2) a' , (3) . S' , double-check .straight balanced . .straight . balanced S S' , balance .8 . 1:1 . 1:N , 5 .9 . , pC , options straight . 10 . Faraday cage , balance setting .

Balanced detection6.2.5 Characteristics balancing balanced detector straight detector . balanced detector .1. points balancign transformer . (6.5)

. 6.7 balance . striaght detection C C , .

Balanced detection v=q/a (6.6) if a>>C and C v(t) 6.7 v(display) overshoot cutoff , . 2 . a straight

(pC) (6.7) pC , n 5.8 pF 6.7 a ,C C . . , a' a , a' a balance . 6.2 a=a' . C+2C=2000pF 2 .

Balanced detection

3 . balanced detector resolution , 1/4 resolution . resolution r straight detection , 3 . 1) resolution 1/4 250 .2) r1/500 . 3) rB/100 B .

sampleStep-up ratioSensitivity(pC)02.00.051nF2.50.0610nF5.00.10100nF15.00.301uF45.01.00

Balanced detection 4 25 50 resolution , resolution 250 1000 . 2500 high resoluton . Resolution , , ( 6.8) .4 . A high rejection ratio m ( m=1000 ) a a' . low-end electrode . high rate . n=100 500 medium rate order . . Terminals . m=3 6.6 s, s .

Balanced detection6.2.6 calibration calibrate 6.9 1 . calibration . ( a a') calibration (6.9 2) calibrate charge stright detection . q cal q point (6.8) (n=a/a'=1) . (6.9) calibration 100pC 50pC .

Calibrators6.3 Calibrators constant : (1) (2) . , . , constant . , . 4 . 1. Square wave generator 2. Portable calibrator 3. Point dischage gap 4. Artificial cavity 6.3.1 Square wave generator square wave generator . e(Figure 6.10) b q=eb . , . . ( ba )

Calibrators6.3.2 Portable calibrator1. . . 2. .3. picofarads .4. Figure 6.10 5060 Hz .5. .: photocell . 6. ; 5, 50, 500 , 5000 pC . (, ba )7. , . resolution . 4 25 resolution 200 s time lag t . resolution r :

Calibrators - impulses per quadrant (6.10) t us . ( ) Figure 6.11. .

6.3.3 Point discharge gap

. Figure 6.12 . counter-electrode . . . , . 15 . 7.5 30 . . - . .

Calibrators , 50 60 Hz . , . . Figure 6.13 . ( . . . .

Calibrators

35 80 50 70 . , , , . . . open .

Calibrators . .

1. (Figure 6.13 ).2. resolution . picocoulomb meter . : . 3. ( ) . .

Calibrators6.3.4 Artificial cavity

Figure 6.15 source . .

Figure 6.15 . 0.1mm 30 mm . 3mm . self-amalgamating . .

Calibrators . artificial cavity . (b in Figure 6.10) . .1. 100pF steps calibrator . . 20% , 500pF .2. Portable calibrator . Table 6.3 .

( rejection ratio ) . ( i.e. 5nF more)

Calibrators

6.3.5

5 b calibration . .

Calibrator Output [pC] Internal Capacitance [pF] (b in Figure 6.10)55050050001101001000

Calibrators(6.11) , , a b . sensitivity level , real level a/(b+a) .

6.4 Interference .

1. : .2. : , . : (1) ;(2) ; (3) ;(4) . 19 .

Interference6.4.1 Mains Mains . supply . .

6.4.2 6.4.2.1 ; . , . , . 6.4.2.2 , . . , ( ) .

Interference

; , (Figure 6.16). .

Figure 6.17 . . . Figure 6.17 .

Interference 6.4.2.3 . . 6.4.2.4 Terminals , Terminals . , terminals, . terminals , , terminals .

6.4.3 Pick-up

. . Faraday cage . Faraday cage cage . Faraday cage : (1) (e.g. ). 80 100dB .

Interference 6.4.3.1 . (Figure 6.18). , , . , , , . ; .

Interference 6.4.3.2 . , . . .

6.4.4 6.4.4.1 , , 50 c/s . .

Interference 6.4.4.2 . . . . , . . . . resolution . (i.g. )(Figure 6. 19). , .

Interference

6.4.5 . . . , , . Table 6.4 ; .