Voltage transmission link for testing EMI susceptibility of a device or circuits

Abstract

The performance of a device under test is observed with and without the presence of controlled EMI fields. Voltage signals from the device under test are transmitted to an oscilloscope by overdamped conductors, a hybrid electrical/optical transmitter, a fiber optic cable, a receiver and a conductor cable. The overdamped conductors are transparent to the EMI fields and the current in those conductors is kept very small by the use of a very high input impedance in the transmitter. The hybrid transmitter may be an analog or a digital transmitter.

Claims

18. The method of claim 17 wherein the step of monitoring the effect of said EMI fields on said device under test further comprises the step of comparing said signal related to the voltages at said points of interest during the selective application of controlled EMI fields to said signal during the absence of said EMI fields..Iadd.

19. The apparatus of claim 18 wherein the first circuit further comprises a light source and a second circuit for operating the light source to produce an optical signal that is linearly related to the input electrical signal..Iaddend..Iadd.20. The apparatus of claim 19 wherein the light source is a light emitting diode..Iaddend..Iadd.21. The apparatus of claim 15 wherein said transmission device further comprises a first circuit for converting the input electrical signal to a corresponding digital optical signal..Iaddend..Iadd.22. The apparatus of claim 15 wherein said conduction means has two signal leads and said transmission device further comprises a differential amplifier, a light emitting diode and a circuit for driving the light emitting diode in response to the differential signals on the signal leads, thereby producing the related optical signals..Iaddend..Iadd.23. The apparatus of claim 22 wherein the optical signals are linearly related to the differentially amplified signal..Iaddend..Iadd.24. The apparatus of claim 3 wherein said monofilament core is a fluoropolymer and the finely divided particles are carbon particles and the core has a diameter of 0.030 inches.

.Iaddend..Iadd.25. The apparatus of claim 1 wherein the conduction means monitors a voltage at a point of interest in the device under test.

.Iaddend..Iadd.26. The apparatus of claim 15 wherein said transmission device further comprises a first circuit for converting the input electrical signal at the port to a corresponding analog optical signal.

.Iaddend..Iadd.27. The method of claim 17 wherein transmitting a signal further comprises converting the electrical signal input to the transmission device to a related optical signal and transmitting the optical signal to a location remote from the device under test.

.Iaddend..Iadd.28. The method of claim 27 further comprising converting the input electrical signal to a linearly related analog optical signal..Iaddend..Iadd.29. The method of claim 27 further comprising converting the electrical signal to a digital optical signal..Iaddend..Iadd.30. The method of claim 17 further comprising applying the controlled EMI field to the device under test and at least a portion of said conductors inside a screen room and monitoring the effect of said EMI fields outside said

screen room..Iaddend..Iadd.31. A connector for electrically connecting an electrically overdamped non-metallic conductor to a device under test to EMI comprising a conductive clip for contacting a test point of the device under test, a coating of insulation extending over the surface of the clip, and a coating of electrically conducting reflective material superimposed over the insulating layer in electrical isolation..Iaddend..Iadd.32. The connector of claim 31 characterized in that the conductive clip is less than or equal to one centimeter in length..Iaddend..Iadd.33. The connector of claim 31 wherein the electrically

conducting material is a metallic paint or metal foil..Iaddend..Iadd.34. A method of coupling a first circuit element to a second circuit element while minimizing the radiation introduced into the second circuit element when operating in a radiation field at selected frequencies about dc comprising:

providing a non-metallic conductor that is electrically overdamped along its length for the radiation field frequencies of interest; and

terminating one end of the conductor in an input circuit in the first circuit element having an impedance that avoids loading the signal source.

.Iaddend..Iadd.35. The method of claim 34 wherein the conductor has a plastic thread core impregnated with fine conducting particles..Iaddend..Iadd.36. The method of claim 34 wherein the conductor has a thread core of a fluoropolymer impregnated with fine carbon particles..Iaddend..Iadd.37. The method of claim 34 wherein the terminating step further comprises providing an operational amplifier in a voltage follower configuration and coupling the one end of the conductor to the input of the operational amplifier..Iaddend..Iadd.38. The method of claim 34 further comprising radiation hardening the first circuit element for the selected radiation field frequencies..Iaddend..Iadd.39. The method of claim 34 further comprising connecting the other end of the conductor to a second circuit element..Iaddend..Iadd.40. The method of claim 34 wherein the providing step further comprises attaching a first non-metallic conductor and a second non-metallic conductor to respective input ports in the first circuit element, the first and second conductors being

electrically overdamped along their length..Iaddend..Iadd.41. The method of claim 40 further comprising connecting the other end of the first conductor to a first point of interest of a second circuit element and connecting the other end of the second non-metallic conductor to a second point of interest of the second circuit element..Iaddend..Iadd.42. The method of claim 40 wherein the providing step further comprises providing the first and second conductors with a plastic thread core impregnated with fine conducting particles..Iaddend..Iadd.43. The method of claim 42 wherein the providing step further comprises providing the first and second conductors with a thread core of a fluoropolymer impregnated with fine carbon particles..Iaddend..Iadd.44. The method of claim 40 wherein the attaching steps further comprise providing respective operational amplifiers in a voltage follower configuration and respectively coupling the one end of the first and second conductors to the respective inputs of the operational amplifiers..Iaddend..Iadd.45. The method of claim 44 further comprising radiation hardening the first circuit element having the high impedance input ports and the respective operational amplifiers for the radiation field frequencies..Iaddend..Iadd.46. The method of claim 40 further comprising monitoring the signals at the first and second points of interest in the second circuit element using the first circuit in response to the radiation field..Iaddend..Iadd.47. The method of claim 46 wherein the monitoring step further comprises determining the effects of the radiation field on the second circuit..Iaddend..Iadd.48. The method of claim 47 wherein monitoring the signals further comprises differentially amplifying in the first circuit element the signals conducted by the first and second non-metallic conductors.

.Iaddend..Iadd. 9. A method of conducting signals at frequencies above dc from a device under test operating within an EMI field to a first circuit remote from the device under test comprising:

providing a conductor made of a non-metallic material electrically overdamped along its length, said non-metallic material comprising a plastic core impregnated with finely divided conductive particles and having an insulating sheath around the core; and

terminating one end of the conductor at an input port of the first circuit having an input impedance that avoids loading the device under test, the other end of the conductor being adapted for receiving a signal from a point of interest on the device under test..Iaddend.