Laptop and welder redux

Get some old 486/Pentium.. test :)

It depends on how well-shielded it is. My office opens onto a weld shop, and sometimes, when they're striking a big arc, my monitor shows me the humongous magnetic field by the display twisting. And this is an IBM monitor, that's all metal under the plastic cabinet!

As usual, the best defense against that stuff is distance - put the laptop in another room, and use shielded, differential pairs for comm, and you should be able to get away with it.

Good Luck! Rich

Magnetic fields are difficult to shield. You'll need u-metal (expensive). I used to work in an office in the centre of Amsterdam. Even on the fifth floor the screen on the monitors moved around a bit every time a tram passed by.

--
Reply to nico@nctdevpuntnl (punt=.)
Bedrijven en winkels vindt U op www.adresboekje.nl

DC fields can in some circumstances cause failure in poorly magnetically u shielded power supplies. I lost a LCD backlight by getting it too close to a fridge magnet.

Ouch. I will try to keep the laptop farther from the welder than I planned. Thanks guys.

i

Exactly. Lots of old 486 laptops around on eBay for under $50.

I assume that since Ignoramus4283 is asking, he values his laptop somewhat.

Michael

In my testing applications, we use a computer (usually a laptop), connected through a parallel port (for the original version), and the serial port (in new versions), to a data acquisition device (Ortmaster or BTS Analyzer). It is in turn connected to a shunt, which may carry up to 25,000 amperes AC for short duration pulses, and 2000 amperes or so continuously.

For the Ortmaster, all units in the field (about 100) use a 1000A, 100 mV shunt, and the parallel port configuration. The installation instructions require a simple test to verify that one side of the shunt is properly grounded. We also recommend grounding the computer power cord to the Ortmaster, and provide an outlet for that purpose. This is for recloser

testing, where output power is usually about 5 to 25 kVA, sometimes at voltages as high as 500 VAC (at up to 50 amps), and currents as high as

5000 amperes (at 5 VAC). These units typically are used in an industrial environment which may include hipot testers up to 50 kV. After about 12

years experience, I don't know of any unusually excessive instances of laptop damage due to the high magnetic fields (which often cause the test cables to jump). Most failures have occurred when, perhaps, a high voltage test lead has arced to the case of the Ortmaster, or where there has been very poor grounding or careless routing of the parallel cable with the test cables.

The BTS Analyzer is now using a newer serial port design, and it is used by technicians to calibrate Breaker Test Sets. They attach a 2500 amp, 50 mV shunt to the output of the test set, run a shielded twisted pair to the

analyzer, and a serial cable to the laptop. The routing of the signal leads is critical, and must be out of the magnetic loop of the shunt. The computer is usually located three to six feet away from the test set output. Here, test currents start at about 1000 amperes continuous, and we use pulses up to 25000 amperes as a regular requirement for calibration. At these levels, even the 480 VAC input cables jump due to the several hundred amperes of current applied for (typically) 5 cycles. These laptops take a beating, as they are often taken on the road through airports and in vehicles to customer sites, so there have been some failures, but none that appear to have been the result of the magnetic fields from the test sets.

Before we used laptops with LCD screens, we used CRTs, and I have seen a display twist several rotations and become unreadable during a test, but always seemed to recover, and the readings were not affected.

Precautions are always wise, however. I would be most concerned about losing data in the hard drive.

Paul (Sent via Google because my news server sucks)