EXPECTED PERFORMANCE, EXAMPLES 
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Example 1, SLAB
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(Hot mtrl, > curie temp)
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In accordance with the specification,
Maximum allowed surface structure,
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PFp-p: GK / 40
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SUPPOSE THAT / DEMANDS
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Maximum allowed surface structure,
consequently, GK / 40 = 1,00 thus,
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PFp-p: 1,00 mm
GK: 40
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CALCULATION
(function of PFp-p), in accordance with the specification,
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Minimum detectable crack depth,
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DJspr: GK / 50 = 40 / 50 = 0,8 mm
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Minimum detectable sliver depth,
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DJsl: < GK / 80 = 40 / 80 =
< 0,5 mm
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Minimum detectable hole diam, Dh:
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< GK / 12 = 40 / 12 = < 3,3 mm
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Minimum detectable crack length,
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Lspr: GK / 1,5 = 40 / 1,5 = 27 mm
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Maximum allowed lift-off, incl shield
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LO: GK / 2 = 40 / 2 = 20 mm
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Example 2, SLAB
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(Hot mtrl, > curie temp)
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In accordance with the specification,
Maximum allowed surface structure,
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PFp-p: GK / 40
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SUPPOSE THAT / DEMANDS
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Maximum allowed surface structure,
consequently, GK / 40 = 0,75 thus,
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PFp-p: 0,75 mm
GK: 30
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CALCULATION
(function of PFp-p), in accordance with the specification,
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Minimum detectable crack depth,
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DJspr: GK / 50 = 30 / 50 = 0,6 mm
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Minimum detectable sliver depth,
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DJsl: < GK / 80 = 30 / 80 =
< 0,4 mm
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Minimum detectable hole diam,
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Dh: < GK / 12 = 30 / 12 = < 2,5 mm
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Minimum detectable crack length
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Lspr: GK / 1,5 = 30 / 1,5 = 20 mm
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Maximum allowed lift-off, incl shield
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LO: GK / 2 = 30 / 2 = 15 mm
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Example 3, BILLET
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(Hot mtrl, > curie temp)
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In accordance with the specification,
Maximum allowed surface structure,
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PFp-p: GK / 40
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SUPPOSE THAT / DEMANDS
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Maximum allowed surface structure,
consequently, GK / 40 = 0,5 thus,
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PFp-p: 0,5 mm
GK: 20
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CALCULATION
(function of PFp-p), in accordance with the specification,
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Minimum detectable crack depth,
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DJspr: GK / 50 = 20 / 50 = 0,40 mm
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Minimum detectable sliver depth,
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DJsl: < GK / 80 = 20 / 80 =
< 0,25 mm
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Minimum detectable hole diam,
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Dh: < GK / 12 = 20 / 12 = < 1,7 mm
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Minimum detectable crack length
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Lspr: GK / 1,5 = 20 / 1,5 = 13,4 mm
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Maximum allowed lift-off, incl shield
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LO: GK / 2 = 20 / 2 = 10 mm
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Example 4, BILLET
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(Hot mtrl, > curie temp)
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In accordance with the specification,
Maximum allowed surface structure,
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PFp-p: GK / 40
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SUPPOSE THAT / DEMANDS
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Maximum allowed surface structure,
consequently, GK / 40 = 0,3 thus,
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PFp-p: 0,3 mm
GK: 12
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CALCULATION
(function of PFp-p), in accordance with the specification,
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Minimum detectable crack depth,
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DJspr: GK / 50 = 12 / 50 = 0,24 mm
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Minimum detectable sliver depth,
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DJsl: < GK / 80 = 12 / 80 =
< 0,15 mm
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Minimum detectable hole diam,
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Dh: < GK / 12 = 12 / 12 = < 1 mm
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Minimum detectable crack length
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Lspr: GK / 1,5 = 12 / 1,5 = 8 mm
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Maximum allowed lift-off, incl shield
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LO: GK / 2 = 12 / 2 = 6 mm
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Example 5, BILLETS
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(Hot mtrl, > curie temp)
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SUPPOSE THAT / DEMANDS
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Minimum detectable crack depth
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DJspr: GK / 50 =  0,50 mm
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CALCULATION
(function of DJspr), in accordance with the specification,
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Consequently, GK / 50 = 0,50 thus,
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GK: 25
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Current penetration depth (optimum),
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DIH: GK / 25 = 25/25 = 1,0 mm
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Carrier frequencies (function of DIH and  ),
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RF: MHZ
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Maximum allowed lift-off, incl shield
Shield + water = 4,5 mm
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LOabs: GK / 2 = 25 / 2 = 12,5 mm
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Maximum available lift-off, free air
Maximum bulges = 3 mm
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LOair+: LO - 4,5 = 8 mm
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Lift off, free space/air
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LOfree: 8 - 3 = 5 mm
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Calculation in accordance with the specification,
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Maximum allowed surface structure,
Ra  PFp-p / 4 = 0,15
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PFp-p: GK / 40 = 25 / 40 = 0,6 mm
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Maximum allowed Ra,
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Ra: 0,15 mm
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Suppose,
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Casting speed
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Vc: 200 mm/s
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Rated speed, sensor
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n: 3000 rpm
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Number of sensor channels/coils
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N: 1
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Consequently, S = 200 x 60 / (1 x 3000) ,
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S: 4 mm
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Calculation in accordance with the specification (S/N > 3),
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Minimum detectable crack length, stat (V=0)
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Lspr: GK / 1,5 = 25 / 1,5 16,7 mm (0 m/s)
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Minimum detectable crack length, dyn (V=0,2)
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Lspr-rot: Lspr + S 20,7 mm
(0,2 m/s)
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Minimum detectable sliver depth,
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DJsl: < GK / 80 = 25 / 80 =
< 0,3 mm
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Minimum detectable hole diam,
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Dh: < GK / 12 = 25 / 12 = < 2 mm
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Example 6, FLAT MACHINED SURFACE
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(Hot and cold mtrl)
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In accordance with the specification,
Maximum allowed surface structure,
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PFp-p: GK / 40
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SUPPOSE THAT / DEMANDS
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Maximum allowed surface structure,
consequently, GK / 40 = 0,15 thus,
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PFp-p: 0,15 mm
GK: 6
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CALCULATION
(function of PFp-p), in accordance with the specification,
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Minimum detectable crack depth,
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DJspr: GK / 50 = 6 / 50 = 0,12 mm
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Minimum detectable sliver depth,
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DJsl: < GK / 80 = 6 / 80 =
< 0,08 mm
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Minimum detectable hole diam,
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Dh: < GK / 12 = 6 / 12 = < 0,50 mm
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Minimum detectable crack length,
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Lspr: GK / 1,5 = 6/ 1,5 = 4 mm
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Maximum allowed lift-off, incl shield
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LO: GK / 2 = 6 / 2 = 3 mm
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Example 7, WIRE, ROD and BAR
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(Hot and cold mtrl)
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In accordance with the specification,
Maximum allowed surface structure,
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PFp-p: GK / 40
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SUPPOSE THAT / DEMANDS
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Maximum allowed surface structure,
consequently, GK / 40 = 0,10 thus,
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PFp-p: 0,10 mm
GK: 4
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CALCULATION
(function of PFp-p), in accordance with the specification,
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Minimum detectable crack depth,
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DJspr: GK / 50 = 4 / 50 = 0,08 mm
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Minimum detectable sliver depth,
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DJsl: < GK / 80 = 4 / 80 =
< 0,05 mm
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Minimum detectable hole diam,
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Dh: < GK / 12 = 4 / 12 = < 0,33 mm
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Minimum detectable crack length,
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Lspr: GK / 1,5 = 4 / 1,5 = 2,7 mm
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Maximum allowed lift-off, incl shield
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LO: GK / 2 = 4 / 2 = 2,0 mm
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Example 8, WIRE, ROD and BAR
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(Hot and cold mtrl)
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Rotating sensors for detection of longitudinal "Long" cracks.
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SUPPOSE THAT / DEMANDS
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Minimum detectable crack depth
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DJspr: GK / 50 = 0,20 mm
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CALCULATION
(function of DJspr), in accordance with the specification,
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Consequently, GK / 50 = 0,20 thus,
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GK: 10
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Current penetration depth (optimum),
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DIH: GK / 25 = 10/25 = 0,4 mm
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Maximum allowed lift-off, incl shield
Shield + water = 2,0 mm
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LOabs: GK / 2 = 10 / 2 = 5,0 mm
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Maximum available lift-off, free air
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LOair+: LO - 2,0 = 5,0 - 2,0 =
3,0 mm
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Radial variation, ovality etc
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DEVtot: +/- < 0,5 mm
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Assumption, radial movement
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dLO: < 0,5 mm
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Minimum lift-off free air (ought to be  1 mm)
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LOair-: LOair+ - (0,5+0,5) = 2,0 mm
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Calculation in accordance with the specification,
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Maximum allowed surface structure,
Ra PFp-p / 5 = 0,05
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PFp-p: GK / 40 = 10 / 40 = 0,25 mm
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Maximum allowed Ra,
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Ra: 0,05 mm
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Suppose,
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Rolling speed / rod speed
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V: 20 m/s
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Rated speed, sensor
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n: 6000 rpm
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Number of channels
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N: 2
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Consequently, S = 20 × 60 / (2 x 6000) ,
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S20: 100 mm
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Calculation in accordance with the specification,
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Minimum detectable crack length,
stat (V=0)
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Lspr: GK / 1,5 = 10 / 1,5 7 mm
(0 m/s)
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Minimum detectable crack length,
dyn (V=5)
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Lspr-rot: Lspr + S5 32 mm (5 m/s)
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Minimum detectable crack length,
dyn (V=10)
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Lspr-rot: Lspr + S10 57 mm
(10 m/s)
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Minimum detectable crack length,
dyn (V=20)
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Lspr-rot: Lspr + S20 107 mm
(20 m/s)
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NOTE: At worst, Lspr-rot 107 mm (20 m/s).
For instance, 50% of cracks, with length 107/2 55 mm,
will also be detected.
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