Ed ...Thanks for the explanation....but the concept of "loop" did not make sense in my testing as the test item was a portable PC, the cable under test a 6-foot serial port cable running to a load box. The PC, cable, and load box were resting on a non-metallic table (not bonded to a platform or copper bench), since the service use is portable by the individual soldier. We did the CS114 test, getting the required RF current onto the shield of the cable near the PC, as required by the MIL-STD. The current then would be much like an antenna current with the PC, cable, and load box being the antenna. The US Army wanted this test. In this case "loop current" makes no sense to me.....Best regards
Jack Gageby, Litton Data Systems Phone 805-532-5413, Fax 805-532-5697 Internet email address: [email protected] ------------- Original Text From: [email protected], on 7/1/98 11:10 AM: --- On Wed, 1 Jul 98 10:39:29 PDT [email protected] wrote: > Ed.... > DNB Engineering in Fullerton has run CS114 for me on several products > while I observed the testing. I do not understand the purpose of the "Loop > circuit impedance characterization" procedure, and neither to they. This > data is not used in the conduct of the test. I have not been able to find > anyone including a PhD who understands why the procedure has these "Loop > circuit impedance characterization" steps. What do you do with this data > after collecting it? No where in the test conduct steps 4(3) on page 65 of > MIL-STD-462D, are any instructions for using this data. Is there someone > out there who knows? Also, what "loop circuit" is the mil std referring > to? > > > Jack Gageby, Litton Data Systems > Phone 805-532-5413, Fax 805-532-5697 > Internet email address: [email protected] > ------------- > Original Text > From: [email protected], on 6/29/98 4:36 PM: > Hi Group! > > I need some help unraveling the calculations associated with the > MIL-STD-462D Method CS114 Loop Circuit Impedance Test. > > Specifically, once you have a table of Forward Applied RF Power (in dBm) > and Observed Injected Current (in dBuA), how do you arrive at the > Normalized Amps per Watt? > > And what is an "Amp per Watt"? Is that a "mho", a unit of conductance? Or > is it a unit of admittance, a Siemen? > > Anybody out there ever really done this science project? > > Ed ---------------End of Original Message----------------- Jack: The "Loop Circuit Impedance Test" is actually called for TWICE in the course of a typical test program; it's buried in both CS114 and CS116. The purpose of CS114 is to check performance of the EUT when exposed to a continuously swept signal. The purpose of CS116 is to check performance of the EUT when exposed to an exponentially damped sine signal. Both methods apply the disruptive energy to the interconnecting cables of the EUT. The idea is to simulate the RF currents which a cable harness may pick up from the environment and conduct into the EUT. The name "Loop..." comes from the concept of the RF current flowing in a loop, or circuit, down the cable, into the EUT, into the platform common chassis structure, through that structure to whatever box is at the other end of the cable that you have be en testing, up through that box, and finally, into the cable. (Remember, the test setup calls for an inductive injection device, clamped around the cable very close to the EUT connector.) Now, what's this all worth? For CS114, ABSOLUTELY NOTHING, IMHO! Dips and peaks might be interesting, but the actual test is constrained by other criteria (a maximum injected power and a maximum induced current). There's no limit on the acquired data, so you CAN'T PASS OR FAIL! For CS116, ABSOLUTELY NOTHING, also IMHO! There is a possibility that the dips and peaks might point out "interesting" frequencies, at which you should inject a test signal consisting of an exponentially damped sine wave with a ring frequency equal to t hat "interesting" frequency. This is exactly what Paragraph 4.c.3.f (on page 78) of Appendix A of MIL-STD-462D says to do. And so does Paragraph 5.3.11.2 (on page 16) of MIL-STD-461D (and also adds 6 standard test frequencies). But, the available test e quipment for generating an exponentially damped sine wave pulse consists of discrete circuits, one optimized for each standard test frequency. So, I can test at 10KHz, 100KHz, 1MHz, 10MHz, 30 MHz and 100MHz. But I can't generate, say, a 6MHz pulse. Face d with this, the procuring agency simply says to test at the standard frequencies. And there goes the last justification for Loop data. -------------------------- Ed Price [email protected] Electromagnetic Compatibility Lab Cubic Defense Systems San Diego, CA. USA 619-505-2780 List-Post: [email protected] Date: 07/01/98 Time: 10:47:28 -------------------------- _
