Cortland:
I didn't get into other details, but yes, we were concerned about human RF exposure at the 225 MHz data link frequency. However, the modulation scheme was very low duty cycle. First, we had a message rate of once per 10 seconds. Then, the individual participant was assigned a time-slot that allowed for roughly a 9 millisecond total message. And the message itself was composed of frames of data, which consisted of digital words made of digital bits (offs and ons). You could sure see it with a Peak detector, but the Average was undetectable. We did measurements with a QP and Average detector, plus measurements with a bolometer type power density meter, in addition to calculating the power from Peak measurements and typical duty cycle values. Every way we looked at it, the human exposure was very low. We tested the soldier-worn system on a mannequin to 461 conditions; there were never any connecting wires, although we did have to supply real-time GPS to the EUT. It was also helpful that the soldier-worn harness also had optical ports that we could use. I would have preferred a mannequin that was more representative of a human torso, but out PVC pipe and foam rubber mannequin produced emission results very similar to a man-worn setup. We also did extensive antenna pattern testing with real humans crawling around in the dirt. The battery is never charged while on the soldier, so the man-worn equipment really has only one mode of operation. The batteries are usually installed before the training session, but a long session might require a field re-supply, so a quantity of batteries could be transported, typically on an HMMWV. Batteries are never charged in the field, or while in the harness, mainly because it's easier to move charged batteries than the chargers themselves. As an aside, we sold systems to the British, and they had us include enhancements such as gadgets that simulated land mines & IED's, so not everything was man-worn. And of course, there were other devices in this product family that were intended for vehicles and weapons, but that testing was similar to traditional 461 testing. The concern about "very long" cables as part of the EUT may be going away. System designers are finally embracing optical cables instead of using a fire-hose sized signal and control cable bundles. OTOH, I was seeing a rise in designs that tried to use COTS Wi-Fi (or similar) to network very local boxes instead of using signal & control cables. There are a lot of EMC problems with this, so we will still have lots of job security. J Ed Price El Cajon, CA USA From: Cortland Richmond [mailto:[email protected]] Sent: Friday, August 24, 2012 6:52 AM To: [email protected] Subject: Re: [PSES] "Smart" Batteries This has been an INTERESTING discussion. I plead guilty to having worded my initial comment poorly; a smart battery must be tested in a configuration that that duplicates the one it is used in, and that exercises each of its functions; the question Bob asked was about, "...batteries that communication with the charger or EUT for charge rates, time left, overheating, etc." That clearly requires some smart batteries be tested inside the powered equipment, first because emissions they create may be shielded by that equipment, and second, because attaching cables for testing in alone adds antennas that both radiate emissions and are more efficient receptors for immunity tests than a battery installed in the powered equipment and shielded by it may be. If an external is used, it would be proper to test that configuration as a stand-alone test as well as running the pwored equipment with them installed.. In Ed's example batteries were normally connected to the powered equipment with wires and it would be appropriate to test that not only with cabling, but perhaps on a mannequin or a human torso equivalent material. Whole body SAR, anyone?. MIL-STD-461 requires wiring and cables used during a test be "representative" of the aircraft wiring. I once saw a system for a cargo/passenger aircraft tested (not my lab -- I was officially an observer and helper on that project) with full-length wiring on pegboards (still an improvement over spaghetti on the table), stacked on top of each other to fit in a chamber. This is not really representative of an aircraft and I suspect few tests of long cables in a chamber really are. That is another issue. The relevance here is that the test should be done in a way that both creates radiators equivalent to the end use and receptors that will deliver equivalent RF to the device under test. There's room here for some enterprising and cash-flush (heh) lab to produce a White Paper. VERY interesting discussion. Cortland Richmond On 8/23/2012 1234, Ken Javor wrote: That is simply not true in the general case. What about a 28 Vdc battery that backs up the essential bus on an aircraft? What about a MANPACK battery that is discharged while being worn, and connected to a mains or generated-powered charger after the mission is over. In the commercial world, what about a battery designed to be used in an UPS? I have purchased several replacement batteries designed to replace the OEM battery in same. Ken Javor Phone: (256) 650-5261 _____ From: Cortland Richmond <mailto:[email protected]> <[email protected]> Reply-To: <mailto:[email protected]> <[email protected]> Date: Thu, 23 Aug 2012 11:58:15 -0400 To: <mailto:[email protected]> <[email protected]> Subject: Re: "Smart" Batteries "Smart" batteries are electronic subassemblies that don't work properly outside of the equipment in which they are meant to be used and must be tested in it. Cortland Richmond On 8/22/2012 1243, [email protected] wrote: - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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