Surveillance Testing Ensures EMP Hardness of Military Systems

Nuclear detonations cause short-lived, intense (e.g., 50 kV/m) electrom agnetic fields over very large areas. Coupling of these fields to electronics can cause upset and/or burnout of components. New military systems require surviv­ ability to EMP in a vein similar to other environmental con­ siderations. Hardening/protection of electronics is accom ­ plished with the use of a variety of specialized components and mitigation techniques. This presentation addresses the develop­ ment and fielding of an instrumentation system and an improved test methodology for assessing the EMP hardness of a military system or facility. Proper operation of most EMP protective measures are not verifiable during normal operations, and thus require special hardness surveillance (HS) activities as a part of hardness maintenance. The development of a cost-effec tive EMP HS measurement set is the culmination of a number of Government and industry EMP testing programs extending over a period of more than a decade. The MIDAS-700 is a self-contained, mobile, integrated data, acquisition system which advances the EMP HS technology. It was specifically developed as a flexible measurement set which can evaluate all types of EMP protec­ tion measures, rapidly, a t low cost and with a minimum of downtime on the system under test. A MIDAS-700 is currently deployed in Europe in support of a NATO test program to perform verification testing, and to establish hardness maintenance baselines on key NATO groundbased facilities. This presentation includes an account of the operational characteristics of MIDAS-700 during this exten­ sive set of surveillance tests. Background Recent modifications to Department of Defense policy regulations require that military systems which perform critical missions in nuclear conflicts must include survivability and hardness features. Most newly developed and deployed systems include nuclear survivability as part of their performance specification. Once a system is deployed, commanders may be required to provide periodic evaluations of the level o f surviv­ ability of equipment for which they are responsible. Nuclear detonations produce short-lived, intense (e.g., 50 kV/m) electrom agnetic fields over very large area. Unlike the thermal and blast e ffects of a detonation which cause damage over ranges of a few miles, EMP effec ts from a high-altitude detonation may be experienced hundreds to thousands of miles from the point of detonation (Figure 1). The EMP fields generate currents and voltages which can cause disruption, upset and component damage within electronic systems. Most new military systems require survivability to EMP. Hardening or protection of electronics is accomplished with a variety of specialized components and mitigation techniques which include electromagnetic shielding, filtering and transient protection. However, these hardening measures can be degraded during the deployment and operation of a system. Degradation can result from wear in normal use, improper maintenance or field modifications intended to improve the system's operational performance. Normal operation and te s t­ ing does not exercise most EMP hardening measures, so special­ ized EMP testing or surveillance is required to assure the system retains its original EMP survivability. Test System Description The MIDAS-700 is a self-contained, mobile, integrated data, acquisition system developed to evaluate all types of EMP protective measures, rapidly, at low cost and with a minimum of downtime and disruption of the system under test. The MIDAS test equipment is housed in a mobile van so that it can test a wide variety of geographically dispersed military systems and ground support facilities (Figure 2). MIDAS testing can usually begin in as little as two hours after the van arrives at the test site. The MIDAS generates stimuli which exercise the EMP protection features of the system with a minimum of risk of damage to the equipment being tested. The response of the EMP protection features is monitored with a variety of probes and sensors. Raw test data is recorded, corrected, reported and stored by an on-board computer with no need of external data transmission or analysis. The van provides all storage for the test components during transit, and is used as an instrumentation control center during test operations. Test electronics and support equipment are mounted in mobile carts which may be operated in the van (Figure 3) or off-loaded with a van-mounted crane for use inside the facility under test (Figure 4). Two operator terminals, one permanently mounted in the van and a second for operation at the test point, are used to initiate, monitor and control the test sequences. Fiber-optic cables provide noisefree communications between the van-mounted instrumentation and external test equipment. MIDAS can operate using facility power at standard U. S. or European voltages, or can generate its own power. For wide-area illumination, MIDAS uses a 200-m eter hybrid dipole antenna to illuminate the entire test object with either vertically or horizontally polarized electromagnetic fields a t a series of discrete frequencies between 0.1 to 100 MHz (Figure 5). The antenna output and test object response are monitored simultaneously by a dual-channel net­ work analyzer to measure at each frequency a vector transfer function between the stimulus and the test object response (Figure 6). The antenna is drivey by a hybrid-switched, solidstate amplifier, and produces field strengths on the order of 1 V/m at the test object. The supporting tower folds into three drums for storage in the van, and can be erected in two to four hours, depending on terrain and weather conditions (Figure 7). EMP Hardness Surveillance Test Methodology The use of low-level CW signals minimizes the disruption to the system under test. Induced signals are below damage levels. Computer control eliminates frequencies which would interfere with normal system operations. Using Fourier trans­ form techniques, the data processing computer extrapolates EMP tim e domain response from the frequency domain response in which the data is acquired. Signals to simulate EMP, either low-level CW or highlevel transient pulses are injected onto cables via specially designed clamp-on transformers. Both the injected reference signal and the response of the cable at the selected test point are monitored. For CW signals, the transfer functions between the reference and the te s t response are measured in the same manner as for wide-area illumination. For transient injection, the actual transient tim e response is recorded with high-speed transient digitizers. The combination of low-level CW and high-level transient pulse injection allows efficient evaluation CH2294-7/86/000-0495 $01.00©1986 IEEE 495