Recently, APELC had the pleasure to install one of our 2m RS105 HEMP simulators at the Naval Information Warfare Center (NIWC) Pacific in San Diego. NIWC states their mission as “Conduct research, development, prototyping, engineering, test and evaluation, installation, and sustainment of integrated information warfare capabilities and services across all warfighting domains with emphasis on Basic and Applied Research and Tactical Systems Afloat and Ashore in order to drive innovation and warfighter information advantage.” As a major part of the test and evaluation component of this mission, NIWC conducts the testing of Naval subsystems under MIL-STD-461G. RS-105 is a unique test under this standard that evaluates the hardness of subsystems against a simulated E1 high-altitude electromagnetic pulse (HEMP). You can read more about this pulse definition in the Increased EMP Threats Lead to Changing Testing Standards blog entry.
We’ve talked in depth about these types of simulators in previous blogs (see: Increased EMP Threats Lead to Changing Testing Standards Part 3: Subsystem testing standards and solutions), but getting the chance to actually discuss the installation process is a fantastic opportunity to get more in-depth about the practical aspects behind setting up these simulators.
Our customer at NIWC found us online and reached out to us looking for an RS-105 HEMP simulator. After a conversation about the types and sizes of EUT they needed to test, we settled on our 2m EUT RS105 system. While APELC is capable of making custom-sized simulators, this particular system was one already existing in our catalog.
It typically takes anywhere from 6-12 months to complete one of these systems at our facility depending on component lead-times, at which point we do a factory acceptance test (FAT) to ensure everything is functioning properly and meeting the standard. We then pack the system using custom, environmentally-sealed crates and ship it off to the customer. In this instance, the system arrived before the customer was quite ready for us to come out and install because they were doing something that was a first for us, and greatly appreciated: installing a very large, very level, concrete pad to install the system on. One of the most difficult parts of getting a system installed is ensuring proper siting for the simulator to live. This is especially true for the 2m RS105 system, given the large footprint of it. See Figure 1 below:
Figure 1 2m RS105 installation footprint
The ground-plane for the system defines the largest part of the of the physical footprint of the simulator given the need for the wire-mesh to extend at least 1.6X the width of the top wires. The above figure represents a rough rectangular approximation of this, although the typical ground plane more closely follows the tapered shape of the wires to save on materials. That said, the effective footprint of the system extends well beyond this boundary, as one other important consideration must be made: electromagnetic interactions with the surrounding environment. This includes two critical considerations:
- Ensuring all large conducting boundaries (walls, containers, buildings etc…) are at least 2X the height of the simulator (as defined by the MIL-STD) from all points on the simulator top plate (wires). More practically, we want to make sure the radiated parts of the pulse do not reflect from these conducting surfaces back into the EUT volume within a time-frame that would create perturbations of the pulse- thereby pushing it out of specification. Knowing that the wave travels at roughly 1ns/ft, we want a distance of at least 25ft to make sure the two-way transit time would put the reflected pulse well into the tail of the pulse (~50ns) so it does not interfere with the FWHM measurement.
- Ensuring sensitive electronic equipment is far enough away to not be affected by the pulse. These systems are sometimes referred to as “bounded wave” simulators because the transverse electromagnetic wave (TEM) is essentially traveling within the bounds of the top-plate and ground plane. However, this is a bit of a misnomer as the high frequency portion of the wave (mainly the rising-edge of the pulse) begins to radiate into free-space once the top plate is ¼ of a wavelength above the ground plane. Therefore, a portion of the pulse is launched outward toward the back, and to some degree, the sides of the simulator. Prior simulations have demonstrated that the field strength begins to fall-off at 1/r2 once the wave goes beyond the ground plane. If we want to make sure no electronics are subjected to a field strength any higher than 500 V/m (a relatively low field given the extremely short pulse), then we want to make sure no sensitive electronics are within 10 meters of the simulator.
The placement of the new concrete pad at NIWC was chosen based upon the above criteria and an ideal site was provided for installation of the system. APELC engineers worked directly with NIWC personnel and provided drawings for the exact placement of anchor points for the guide wires and poles so that these could be planned around during the laying of the rebar and concrete. Once the concrete pad was poured and cured, the first team from APELC came on-site to install the system. This included our mechanical engineer along with a team of highly-experienced technicians to install the majority of system components.
The first step in this process involved cutting away small portions of the ground-plane and drilling holes into the concrete for the anchor points. APELC personnel used highly accurate methods to ensure the placement of the holes fell within +/- 1cm tolerance. Threaded concrete anchors are then set into the holes to provide for easily removable hardware should the system need to be taken down and stored.
Figure 2 Hole drilled into the concrete for an anchor point
After the anchor points are set, the two main poles are raised into place and bolted into the ground. Guide wires and temporary straps are also set into place to ensure stability of the poles until the catenary system is installed to maintain tension.
Figure 3 Raising the poles
Figure 4 Installing the tensioning system for the catenary
The top wires are all cut-to-length and terminated on-site after the poles have been installed to ensure any uncertainties within the pad installation have been accounted for and all wires can be evenly tensioned to provide a uniform profile.
Figure 5 Terminating the wires with schwaged connectors
The top wires are then attached to the phillystran catenary where the transition is made to the load curtain resistors. As can be seen in the picture below, the top wires can then be easily raised or lowered using the cranks at the base of the poles.
Figure 6 Preparing for attachment of the wires to the catenary
Finally, the wires are terminated at the launch structure, where the tension of the wires is held on the input side of the system. The launch structure is made to be mounted to the concrete, providing a method to easily attach or remove the pulse generator without affecting the tension on the wires.
Figure 7 Attachment of the top wires to the launch structure
Once the wires are properly tensioned and set, the system can easily be taken down or set back up by the customer without the need for a man-lift. To completely lower and/or remove the system, the top wires are simply brought down using the cranks at the base of the poles, and the poles can be brought down by unbolting the hardware that secures the hinge at the pole bases and lowering the poles down to the ground using the hinge as a fixed pivot point to safely bring down the poles without the bottom kicking out.
Figure 8 Completed 2m RS105 system installed at NIWC Pacific
With the system completely installed by the first crew, some initial testing of the Marx generator and controls is performed and then it is time for the second visit.
In this instance, the second “crew” was only one person (Matt Lara), as the work to be performed involved ensuring the simulator met specification and training the personnel on the operation and calibration of the system.
Two probes are used in the testing of the system: the ground plane reference probe located at the output of the peaking circuit/launch point and the free-field d-dot probe shown in the figure below. Analog fiber-optic links are used to transfer the d-dot signal to the oscilloscope without coupling in significant common-mode noise, as would be the case if coaxial cable was used to make the 75 foot run from the EUT volume to the tunnel the oscilloscope and controls are contained in.
Figure 9 Free-field d-dot probe and fiber-optic link in the EUT volume
During this portion of the commissioning process, the system is calibrated to determine the exact settings for the system at this location. This includes determining the pressure, voltage, and peaking gap settings to achieve the full range of field-strengths up to 50 kV/m in the EUT volume. The APELC data acquisition software shown in the figure below collects the data from the customer’s oscilloscope, integrates, scales and displays the results for field strength, pulser output voltage (reference probe), rise-time and full-width half-max (FWHM). Using this data, the correct specifications can be accurately verified and reported.
Figure 10 APELC data acquisition and reporting software
With the final commissioning of the system complete, APELC provides the customer with all the necessary training and information to effectively use the system. In this particular instance, APELC has further agreed to come out for an additional visit to support the first customer test at NIWC.
