Test Equipment (3)

Question 1

Three main categories of ET test instruments:

Answer 1

• Conductivity Testers
• Crack Detectors
• Multi Purpose Instruments

Question 2

Conductivity Tester

Answer 2

• Originally analog (needle) indicating IACS%
• CRT displays, elliptical shaped signals -> flying vector dot trace graph
• LCD vector dot trace graph
• Digital numeric displaced via LED or LCD

Question 3

Crack Detectors

Answer 3

• Originally analog (needle) single frequency with manually adjusted “balance” controls.
• When a crack is detected/eddy current disrupted = change in impedance and the needle would be deflected (bridge became unbalanced)
• CRT 1930-1980 Oscilloscopes (elliptical display)

Question 4

Multi Purpose Instruments

Answer 4

Phase angle discrimination modulation circuitry, CRT instruments became multi purpose

• displaying both conductivity and cracks + thickness measurement, hardness and heat treat testing
• from the replacement of elliptical signal to “flying” vector dot displays

Question 5

Describe the “flying dot” display

Answer 5

• dot = operating point, can be positioned/balanced on the screen
• dot would then “fly” leaving a trace signal facilitating phase angle analysis changes similar to the changes on the impedance vector in an impedance plane diagram.
• length of trace = amount of impedance change resultant of amount of eddy current disruption