by Joanna Hill
Today is Arnold’s first day at Mega Automotive. He is fresh out of college with an electrical engineering degree and is eager to meet his new boss, Mr. Buttsworth.
Mr. Buttsworth: Hello Arnold welcome to Mega Automotive. I’m sure you’re going to like it here. It’s a fast-paced environment with lots to learn and loads of good people to work with. We have an exciting new position for you it’s called a Component Electromagnetic Compatibility Engineer. Your job is to prevent electromagnetic compatibility failures at final vehicle testing. We design the vehicle and many of the components. Some of the components are designed and manufactured by suppliers. After all the parts have been designed they are assembled into prototype vehicles. These vehicles are then tested to make sure they can meet all sorts of requirements; one of these requirements is electromagnetic compatibility.
First, you must understand the specific EMC tests we perform on a vehicle are considered a company intellectual property and you are not allowed to disclose these requirements outside of the company.
Arnold, your first assignment will be to test an engine controller for EMC as a component. You are to develop a component level test plan to catch the EMC issues so they can be fixed early in the programs rather then at the end of a program. It is very expensive to make any last minute changes.
This is what an Engine Control Unit looks like, we call it an ECU.
Figure 1 – An Engine Control Unit (ECU) from a 1996 Chevrolet Beretta courtesy of Delco Electronics and Wikipedia.
Arnold: Cool, I love working on cars. It’ll be great fun to work on them for a living. What exactly is EMC?
Mr. Buttsworth: Our vehicles are put into a lot of different electromagnetic fields created by a lot of different devices. Many of these devices are “self-certified’. In fact, automobiles are also “self-certified”. That means that Mega Automotive is obligated to make sure a vehicle will work correctly when exposed to the fields that it may encounter and not interfere with any other device. The problem is that not all of the companies making things are as diligent as we are here at Mega Automotive.
For example, farms can have a water sprinkler called a Pivot that is driven by a three phase, 480 volt, Variable Frequency Drive. The VFD takes in 60 Hz AC and makes whatever frequency you want at 480 volts and 800 amps. The variable frequency is used to drive the pump motor of the sprinkler. The VFD does this by rectifying the three phases with a bank of diodes and capacitors. Then this DC voltage is pulse width modulated to feed a three phase motor that drives the water pump. If any of the case ground connections in the wet and dirty farm environment gets rusty, a PN junction is formed in the ground path. This splatters RF noise all over the spectrum. To make matters worse, the pump drives water into a 16 foot high quarter mile long water pipe.
The farmer thinks of this as an agricultural sized water sprinkler, we know it as a folded monopole antenna driven by lots of high frequency PWM noise. The Farmer has no idea he is creating huge electromagnetic fields that can interfere with all sorts of devices including vehicles. And to make matters worse, occasionally this quarter mile long short wave antenna with taps every 50 feet made up of an A-frame with two tractor tires to elevate the water pipe is parallel to the highway! Never the less our vehicles driving by within 100 feet of this antenna are not allowed to misbehave.
Your job is to come up with a component level EMC test to make sure that when the initial prototype is assembled and tested there will not be any issues with EMC.
Arnold: Okay, can I see the harness of wires that will be connected to the ECU?
Mr. Buttsworth: No, it has not been designed yet.
Arnold: Okay, can I know how many harnesses will be connected to the ECU?
Mr. Buttsworth: No, it has not been designed yet.
Arnold: Are there things connected to this unknown harness?
Mr. Buttsworth: Yes, we know what kind of sensors and actuators will be connected to the ECU and we have the documents that describe their function, but we don’t actually have any of then yet. They’re all in design as we speak.
Arnold: Okay, can I see the schematic of the ECU?
Mr. Buttsworth: No, it has not been designed yet.
Arnold: What can I know about this thing?
Mr. Buttsworth: We know the pinout and we have a description of the engine control system. After the harness has been designed and routed on the engine and when we find out how the engine group is going to ground the ECU, it will be assemble into a prototype vehicle and it has to pass the vehicle EMC testing.
Let me show you to your desk. We will have a computer for you shortly. In the mean time please read these documents. And here is your list of mandatory safety and company training classes.
Barney: Hello Arnold, welcome to the neighborhood. I hear you’re the new EMC component engineer. I do the vehicle level EMC testing.
Arnold: Oh boy am I glad to meet you. I am to develop an EMC test to prevent issues from showing up in your EMC testing. But I have to do this without knowing how the thing is going to be wired up. This is impossible.
Barney: Actually our job is to write test plans that specifies the EMC test that need to be run by EMC technicians. The EMC equipment itself is very expensive and getting chamber time is really hard. So we write an EMC test plan, it gets approved, and then it is performed by the technicians.
All you have to do is come up with an idealized harness with a load box to simulate the sensors and actuators at the end of the harness. Make the harness about half a wavelength long in the FM band and pass on the test equipment design to the test equipment group. Tell them to test for stuck at one and zero for all loads.
It’s not really that hard if you don’t get too picky about simulating the vehicle. We have no idea what it will look like at this point, but never the less it has to pass my vehicle level EMC test to be sold. And we cannot delay the first day of production of the vehicle if it fails the EMC testing. As a result we almost always end up working nights and weekends to get it out the door in time.
Good luck and welcome to automotive. It’s not for everyone, but I love to see my vehicles on the show room floor or on the road. You know you had a part of making it happen. We have lunch down in the cafeteria. I’ll come by around noon to show you where it is. By the way, the hardest part of the job is staying awake while you read all of the documentation. See you at noon.
Epilogue
After many years of trial and error, Arnold came up with a technique to test modules for EMC before the vehicle design was complete. At the same time others were also working to solve the same problem thoughout the industry. But as you can expect, their solutions were all different. Some demanded the load box be in plastic, where others wanted metal. All of these empirical techniques work, sort of. But still at the end of a vehicle program, it must pass an EMC test.
Disclaimer, the individuals named in this article are fictional, any reference to actual people or companies is unintended.
Joanna Hill holds a MSEE from Georgia Institute of Technology and a BSEE from Florida Institute of Technology. She turns the magic of EMC into the technology of EMC with consulting and classes globally. Her classes have demystified EMC in China, Mexico, Germany and the United States.
She is a member of the IEEE, IEEE EMC Society, SWE, SAE EMI Task Force, ISO TC22/SC3/WG3 USTAG, and CISPR/D USTAG. And a member of the IEEE EMC Society board of directors. She has worked as an engineer for 39 years always with an interest in fields and waves. Her LinkedIn page URL is:www.linkedin.com/in/JoannaEMC. She may be contacted at: [email protected].
