To properly test any system, subsystem, or IC, you need to measure the voltage waveform used to test a DUT. Unfortunately, typical oscilloscope setups can yield incorrect results. You need to know how to properly trigger an oscilloscope. Plus, you need to get the most from an oscilloscope's vertical resolution to maximize test results.
Automotive EMC (electromagnetic compatibility) specifications typically reference ISO 10605:2008 in describing test setups, procedures, and equipment. Equipment includes an ESD simulator whose components such as the RC networks produce waveforms that represent human ESD models. ISO 10605 also provides a method for verifying ESD simulators. The method assures test repeatability over time and among multiple laboratories and/or ESD simulators from various manufacturers. Proper oscilloscope setup is essential to correctly assess ESD simulator outputs.
ISO 10605 specifies ESD test levels from 2 kV to 25 kV in both polarities. Typically, you apply test voltages in steps by increasing the voltage to an established limit. In addition, you must subject component surfaces, interfaces, and electrical terminals to direct air and contact discharges while unpowered, and while configured and operating in a predetermined mode. The component, while powered, may also be exposed to indirect discharges that produce a radiated disturbance. The component needs monitoring for deviations in operation as well as inspected for damage or degradation of performance upon test completion. Similar procedures are also performed to the full vehicle.
The verification of the ESD simulator includes characterizing the discharge pulse waveform. The second edition of ISO 10605 identifies rise time, first peak current, current at t1 and current at t2 as the parameters of interest (Figure 1). The values of t1 and t2 vary with the value of R and C in a given RC network for the purpose of verifying its time constant.
Figure 1. Measurement parameters of interest include rise time, first peak current, current at t1, and current at t2 on