Analog Device Testing: Test with an op amp. From the "A" point "virtual ground" concept: ∵ Ix = Iref, ∴ Rx = Vs / V0 * Rref, Vs, Rref excitation source respectively, the instrument calculates the resistance. Measured V0, then Rx can be obtained. If the measured Rx is capacitance, inductance, then Vs AC signal source, Rx for the impedance form, the same can be obtained C or L.
Guarding: The above test method is for a separate device, and the actual circuit devices are connected to each other, so that Ix 笽 ref, test must be isolated (Guarding). Isolation is the basic technology for online testing. Test, as long as the G and F point with the potential, R2 no current flows, there is still Ix = Iref, Rx equation unchanged. G point to ground, because F point to the virtual, two potential equal, you can achieve isolation. Practical and practical, through an isolated operational amplifier so that G and F and other potential. ICT tester can provide a lot of isolation points, eliminating the impact of the external circuit on the test.
IC test: For digital IC, using Vector (vector) test. Vector test is similar to the truth table measurement, excitation input vector, measure the output vector, through the actual logic function test to judge the quality of the device. Such as the NAND gate of the test of the analog IC test, according to the actual function of IC excitation voltage, current, measure the corresponding output, as a functional block test.