For instance, if there is nominally 28 V on a discrete input, we should use a TVS with a working voltage above 28 V (say 33 V). In the example seem in Figure 4, we will use a 10-ohm series impedance and will be trying to select the proper TVS.įigure 4: Example of WF5a Level 3 Pin InjectionĬalculating Peak Pulsed Power for DO-160 Pin Injectionįirst, we need to decide what working voltage we want in a TVS.
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The next thing you need to know is your unit’s series impedance and the TVS you will use to protect your device. To determine the source impedance simply divide the V OC by the I SC. This is equivalent to a voltage source of 300 V with a 5-ohm source impedance. At level 4 it has a V OC of 750 V and an I SC of 125 A. The first thing you need to know is the transient generator’s test level and source impedance. For category A4, waveform 4 is applied. To calculate pin injection on your unit, you need to know a few things. Pin injection can be calculated and simulated quite easily. These nonlinear devices will start to clamp the voltage driving the current higher. If this seems rather vague and unspecific don’t worry.
In the case of your test pin you are somewhere in between high impedance and a dead short, and as such, you will see both less voltage and less current.Īdditionally, your design would be wise to include protection devices such as TVS diodes. Remember that during calibration 1500 V was only achieved because the circuit was high impedance. 60 A was only achieved because the circuit was a complete dead short. Though pin injection category A4 shows waveform 3 at 1500 V and 60 A, when applying this energy to each pin, you should not expect to see either of these levels.
This allows for a simple set up and very little test support equipment. Often, if the device is simple, the aircraft manufacturer or certification authority may allow your unit to be unpowered during the test. Typically, this test is a damage tolerance test and as such your unit is not required to operate through. The calibrated level is applied to each pin of your unit in both the positive and negative polarity, ten times each.
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The lightning generator test point is then applied to each pin of your unit and the amplitude is set to the predetermined level during the calibration. Once both these are achieved the calibration amplitude is recorded. Using that same generator amplitude in a short circuit condition, the calibration should achieve the short circuit current requirement level. The waveform generator’s amplitude is increased until an open circuit voltage at the required level is achieved. The V OC represents an open circuit voltage and the I SC represents a short circuit current. Pin injection uses a fixed energy level, calibrated before the test and applies it to each pin of your unit.
Testing pin injection to A4 means that category A will require you to test against waveform 3 and waveform 4 at pin injection level 4. An example is shown in Figure 2 and Figure 3.įigure 2: DO-160 Table 22-1.1 Pin Injection Waveform Setįigure 3: DO-160 Table 22-2 Pin Injection Levels However previous revisions of DO-160 combine the letter designation for cable bundle and multiple burst. In this example from DO-160 revision G, A4 represents the pin injection requirement, G4 represents the cable bundle single and multiple stroke requirement and 元 represents the multiple burst requirement. A requirement from an aircraft manufacturer will look like Figure 1, in DO–160 revision G.įigure 1: DO-160 Section 22.0 Category Explanation While single/multiple stroke and multiple burst represent a real-life occurrence where energy is coupled on to a cable bundle routed along aircraft, pin injection is less rooted in a realistic scenario but provides a simple and foolproof way to test the robustness of one’s product. DO-160 is broken down into three sections pin injection, single/multiple stroke, and multiple burst. In this post we will examine lightning induced transient susceptibility or indirect lightning as the design constraints around indirect lightning have a significant impact on other sections such as power input.Īs mentioned in my previous overview post, indirect lightning simulates the coupling of energy onto a unit’s interconnecting cables in the event of a lightning strike. These four sections make up the most critical sections of DO-160 because of their complexity and, as a result, the risk of failure.
Sect 22.0 – Lightning Induced Transient Susceptibility (Pin Injection and Cable Bundle) Sect 21.0 – Emission of Radio Frequency Energy Sect 20.0 – Radio Frequency Susceptibility (Radiated and Conducted) In my first article, I gave an overview of RTCA’s DO-160 and the electrical EMC sections that it entails. In the next few articles I will be discussing the most critical EMC section of DO-160.
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