It rolls out in acres and covers millions of square meters of the planet. It is shiny and it is matte, it is gaudy and it is sublime, it is cheap and it is expensive, it is laid in homes, offices and schools and on surface ships and submarines. It has a fascinating history, made early-on from linseed oil and first conceived as a substitute for Indian rubber. According to Armstrong©, it is a ‘green’ material, “made from natural materials like linseed oil, recycled wood flour, cork dust and limestone.”1
It is Linoleum.
How does this common stuff intersect with the world of electromagnetic interference? And who ponders such questions? Well, I do, and those that make the stuff know that a stray bolt or staple will ruin the intricate presses that mold and form the patterns in the flooring that covers offices, kitchens, bathrooms and battleships.
EMC is pretty cool because one gets to learn a little about a lot and an outing to Ben Franklin’s city a few years ago informed me on a few things, namely: listen carefully to the customer, never assume anything and be careful what you order for lunch.
A couple of Januarys ago, we were called to a scruffy area of Philly, cruising early one morning from DC and found our client’s building: a pre-World War II low-slung faded red brick industrial building with steel-framed windows that hadn’t been washed since Kennedy was President. A slightly-sweet odor hung in the cold air. Equipment groaned from inside the building and steam spat from corroded ventilation pipes, swirling and dissipating against the cold clear blue sky.
The creaking factory that made the flooring was suffering from ‘noise of uncertain origin’ that was causing one of the manufacturing lines to shut down. We arrived early in the morning and were greeted by Sal Monachino, a third generation import from Sicily with a thick Philadelphia accent and strong arms the size of tree limbs bulging under a heavy open-collared denim work shirt. I was attired engineer-style, khakis, a wide curry-yellow tie (my *best*) and an off-the-shelf jacket as I’ve found that it’s always better to be over-dressed than under-dressed seeing as it’s easier to take off the tie than to wish you had one.
“You guys the noise guys?” he asked, sizing us up.
“Well, we hope you can help us out.” He waved us to follow him into the factory. “Line three has been shut down for a couple of weeks and my bosses are pretty pissed-off.”
We followed Sal down a maze of fading painted cinder block hallways. This was a working factory. Real stuff was made here, far removed from the high-tech corridors of the previous week’s work. I am sure that we were wearing the only ties in the whole joint.
“You can put your stuff down in here.” Sal turned the doorknob and swung open the door to a small conference room and hit the light switch; three out of the four fluorescent fixtures flickered on. There were five or
six mis-matched chairs—also seemingly from the Kennedy era—arranged around a battered dark green Formica-covered table.
“I’ll get the plant manager and a couple of other guys,” Sal said. “Help yourself to the coffee over there.” We put down our briefcases and walked to the coffee pot, which looked like it was washed about the same time as the windows, steaming with a thick stinky black liquid. There was a stack of small Styrofoam cups next to the coffee pot. I pulled two free and loaded them with dry creamer and a load of sugar, making it drinkable.
Sal came in a few minutes later with three other guys, less burly, obviously office-types and motioned for us to sit down. The tallest one had a nervous tic that caused his right eye to twitch.
“I’m Pat Megroin, plant manager.” We shook hands and exchanged cards. We all sat down, Pat cleared his throat and started explaining his troubles.
“Line three has been down for the last couple of weeks and it’s costing a lot in late orders, ticked off customers and frustrated owners.” He paused, coughing slightly. “The line should be producing three thousand lineal feet per day, but we’re barely getting five hundred. It keeps shutting itself down.”
What’s the symptom? we asked.
“The real trouble started about the time we installed a new crane in the area.”
Sal nodded in agreement.
“You see, our product is printed, in a way, using a roll press that has been designed to form the patterns and colorize the product. These presses cost thousands of dollars. If something gets caught in the material, it can damage the surface of the press, so we have a magnetometer system to make sure no stray bolts or staples or what-have-you get into the production line.”
Sal picked up the explanation and started sketching on a sheet of paper. “The magnetometer has a drive loop antenna, the ‘source’ and a receive or ‘sense’ antenna. If a piece of metal gets onto the sheet of material, the sense side detects the change in magnetic field and shuts the press down before the material can get wound up into the roll.” Sal sketched something like Figure 1.
Figure 1: Sal’s sketch
“The receive antenna has to be pretty sensitive because the line runs so quickly. Even a quarter-twenty nut can ruin a press and shut us down.”
So what’s with the crane? we asked.
Pat picked up the discussion. “The crane was part of a general overhaul on Line 3. The drive is electronic and we think it’s spitting out a bunch of noise and getting into the magnetometer.”
He looked down, shook his head slowly. “A quarter million dollars in that crane. My boss is about ready to throw it into the Schuylkill.”
“Can you help us?” Pat asked.
We looked at each other and said we’d try.
“Great,” Pat said. “We have a call with the owners at three p.m.” Pat glanced at his watch, rose from his chair. “Hope you guys can figure this out.”
Great, we thought, a whole six hours to fix this.
We unloaded the spectrum analyzer and cables and antennas and other gear from the station wagon and lugged it through the plant, past hissing spitting valves, oozing cauldrons of whitish goo, under and around plumbing and wire races. Sal yelled over the din: “This is line 2. It’s working great, you can see. Here’s the press.” Spinning rolls of material were squeezed under pressure as yards and yards of material looped through the line.
Line 3 lay ahead and as much as Line 2 was alive, Line 3 was dead. Material hung like shrouds, loose and limp. Covers were off a dozen inspection points.
Sal showed us the main press. The shiny stainless steel cylinder had an intricately-etched pattern in it. “This is our biggest seller. The DIY guys buy miles and miles of this stuff.” He paused, adding, “When we can make it…”
“This is the magnetic sensor.” Sal banged on a long box ran along the width of the material. A similar box ran underneath. “The loops are in each of these boxes and are connected to the driver and receiver over there.” He pointed to a gray NEMA enclosure bolted to a column. A couple of black coax cables ran from the long boxes, under and into the enclosure.
“The frickin’ crane is there.” He pointed overhead. A gleaming yellow I-beam was hung on tracks. The trolley was positioned in the middle, a loop of cables connected it to the runways that were bolted to the sides of the building.
“All of the electronics are inside the trolley. Ever since we had that thing installed, this line hasn’t run right.” Sal harrumphed. “Piece of *&%#,” he added for emphasis.
We unpacked our gear and set things up. We would take a look at the radiated spectrum, just to get a feel for what was happening. We asked if we could run Line 3. He shook his head. “It’ll take hours to get her going and the bosses need an answer today.”
We shrugged our shoulders and looked at each other. Sal then brought over a tall smiling guy in work overalls with ‘Victor’ stitched above his breast pocket. “Call me Vic!” he said, pumping our hands. “Whatever youse need, lemme know!”
We asked Vic to start to move the trolley. He picked up the pendant. “Youse want the bridge, the trolley or the lift?”
Bridge first. Vic nodded and punched the button. The bridge started up, moving smartly along the rails. The analyzer display jumped. The new bridge employed solid-state drivers, new-at-the-time IGBT devices with wicked-fast slew rates and noise spectra that impressed.
We tried some stuff. We climbed the crane. We snapped on ferrites we had on any wire we could think of, we tried some shielding and grounding, this noise fay just laughed. Nothing made any difference; if the crane drive really was the problem, a field retrofit wasn’t going to do much anyway.
It’s hard to walk away from a nettlesome problem, a bastard thing that defies a solution. But we kept looking, tried and abandoned reasoning and mostly kept guessing, but with no great reveal.
Lunchtime came very quickly and we re-assembled in the conference room. Sal was surly. “Nothing yet, consultants?” We shrugged, gave him a quick rundown of what we found—rather what we didn’t find. Sal softened a little. “Hell, let’s go to lunch. It’s Mary’s twentieth year at the plant, so I want to take her, too.” He winked at me. “Someplace classy. I’ll go get her.”
We bundled up and left the plant, our breath icing in the air as we trod three blocks to Manny’s Steak and Shake, a dive that as Sal told it “fed my father and my father’s father when they worked at the plant.” The place held about twelve tables, faded candy-apply red with vinyl-cushioned chrome-framed seats that squeaked as we sat down.
The waitress came over to the table. She looked to be in her early fifties, a sizable gal with a big smile, fake-black hair and a big bosom. She gave Sal a hug. He beamed, clearly enjoying her…suppleness.
“Hello gorgeous,” he crooned.
“Hello handsome. The usual?”
“Yeah, Marge, the special.” He looked at us. “If it’s Tuesday, it’s meatloaf.”
“Sure, honey. And the rest of you guys?” she polled.
Pat took the fried chicken, Mary the fruit plate (cantaloupe, strawberries and cottage cheese). The meatball sub looked good to me.
Meatball sub: what not to order with a first-time client. It came on a large oval plate with a heap of crinkly fries that glistened with oil. Marge laid it in front of me. “Enjoy, sweetie, specialty of the house.” The sub lay splayed open, four large meatballs slathered in tomato sauce, rich mozzarella oozed from the roll. The edges of the roll lightly toasted.
Sal dug into the meatloaf, Mary toyed with her cottage cheese and I picked up the long sandwich, trying to negotiate a bite. I over-reached and the end-meatball, dripping with marinara, popped loosed and *blip* landed square on my chest. Sal burst out laughing. “So much for your fancy yellow tie!”
Next time I’ll have a salad, I told myself, daubing a wet napkin on the spreading red blotch. I removed the stained garment and rolled it up into my pocket. We finished lunch and walked back to the plant, three p.m. coming quickly upon us.
At some point it becomes pointless to try to make measurements and it’s important to talk with and listen to the client. Maybe we were over-looking something. We asked ‘when the crane was put in, what else was done to the line?’
Sal replied, “Um, we did PM on the line, changed a bunch of belts, lubed the bearings on the big drive, right Vic?”
Vic replied. “And calibrated the magnetometer.”
Can we have a look at that? we asked.
Sal shrugged. “Sure.” We wandered over to the NEMA enclosure. The device was pretty simple: a circuit board, a couple of transformers and some RF circuitry. A pair of BNC connectors were mounted on a bulkhead, marked “IN” and “OUT”.
“The drive signal goes to one loop from the OUT.” He pointed at a red connector. “The received signal comes into here.” He tapped a blue connector. Red out, blue in. We asked to see the business end of the system, the loop antennas. For this, we lay down and squirmed up under the line. I was the junior guy (not so much now) so it was my job to scrunch under. Sal handed me a flashlight mumbling, “Not sure what you’re looking for…”
I wasn’t so sure myself.
The two coax cables ran alongside each other. I followed the wiring to a bulkhead and looked at the connections.
“Red in, right? Blue out?” I shouted back at Sal.
Sal replied, “Yeah, that’s right.”
The in and the out were reversed, so the multiple-turn loop, the source, was connected to the sense input, the many turns of wiring greatly amplifying any stray noise that may be in the area.
Sal was nonplussed. “Holy cr*p. When the guys calibrated this thing, they put it back together backwards!” He shook his head and mumbled, “Geez. Wasn’t the crane after all.”
Indeed, the crane was vindicated. I flipped the connectors, the conference call went off with the good news that Line 3 was back up and the guys with the jackets and one tomato-spattered tie were done headed home.
Sometimes, “EMI problems” don’t require ferrites, shielding or grounding to resolve, but listening to the client and having a bit of fortuity.
Just sometimes, as my pop used to say, “It doesn’t matter if you’re lucky or skillful, as long as you’re effective.”
|Mike Violette, P.E.
is founder of Washington Labs and American Certification Body and he never bought another yellow tie. He can be reached at firstname.lastname@example.org