When performing EMC testing in a test chamber, it is essential to monitor the EUT/DUT (Equipment Under Test/Device Under Test) without affecting the test or support equipment. The simplest form of monitoring is to observe the DUT directly. Of course, this cannot be done in a closed windowless test chamber. Cameras are used, but the camera must not affect the test for emissions measurements or be affected by the immunity subjected to the DUT. Unique camera systems have been developed for harsh EMC test environments. For times when data or communications need to be sent to or read from the DUT, optical communication links are used to isolate and not affect support equipment.
The reasoning for using fiberoptic isolation for these devices is that removing a wired connection removes the possibility of any RF energy running from inside to outside the chamber or vice versa. It goes without saying that wireless transmission is not possible through a chamber as it can affect testing or be corrupted by the EMC immunity. Testing and passing EMC is challenging enough; it is important to use the correct tools to be sure non-test issues do not give you false measurements/failures. Using EMI-hardened optical links gives the best possible setup and control.
The theory is the same whether it is an Optical Camera or an Optical Communication link. Transfer a signal to light in a fiber optic cable and then recompile the signal from light to a usable signal on the other end.
There are many types of Optical transmitters/receivers or transceivers available. Here is a list of many common types:
| HD Camera | CAN FD | A2B | RS232 |
| 4k Camera | CAN HD | FLEX | RS485 |
| IR Cameras | CAN SW | Automotive Ethernet | RS422 |
| 1-Way Audio | CAN LS | Ethernet 1Gbit | USB 2.0 |
| 2-Way Audio | SENT | TTL | USB 3.0 |
| Analog links: | LIN | UART | LVDS |
| 100kHz- 50MHz | SPI | 1394 | HDMI |
New fiber links are developed as new communications are approved and become available. Always ask the manufacturer for the optical link you need, even if you do not see it in their marketing.
Here are the important questions to ask when making your selections.
What level of EMI shielding is provided?
The transponders are developed and tested to meet a certain immunity level. In many cases, this is to a level of >200V/m. This level may be a magnitude higher than you need. But one is insured the unit will be immune and not a weak part of the setup. Manufacturers of EMI fiber links will only offer one immunity level. If they were to offer options for different levels with different price points, this would ultimately increase the overall prices and cost for all items since volumes are low. Having a single design for most applications helps keep costs down. Some applications call for higher immunity levels, like testing in HIRF with pulsed fields of 600V/m or higher. In this special case, special units are available.
What EMC standards do they comply with?
For emissions, the EMI fiberoptic links also must not emit RF, which may contribute to the EMI emissions measurement taken in the chamber. Many times CISPR 25 is used based on its low limit levels. Because of the high shielding and isolation of the links, this is normally not an issue but should always be checked.
What type of connectors do they use?
The fiber links will utilize highly shielded connectors to maintain robust shielding. The FSMA has proven to produce the best solution for fiber connection. However, other connections, such as ST, can be used without issue but depend on the application. You may want to use connectors and match your systems for easy swapping from chamber to chamber, as running the fibers each time may be time-consuming. EMI fiberoptic link manufacturers should accommodate your needs. Be sure to ask.
Understanding what connectors are used for communication and connection to your DUT is also important. Can you connect directly to the box? Or are specialized shielded connectors used? In these cases, adaptor cables are required and need to be supplied with the links. One should double-check the pinouts of adaptor cables to match your needs. Otherwise, these can be modified before delivery.
What size is the link/camera and associated equipment?
The size of the links may be important in some applications. Using many links with one DUT can quickly become cluttered with links on the test table or over the vehicle. Having a small portable link is critical. This is also important for cameras if they need to be positioned in a vehicle and where many cameras are needed to see different parts of an instrument panel. Cameras normally require external battery packs adding to the size and bulk of the setup. Having a compact battery pack that can easily stack and sit out of the way is critical. Make sure this is all accounted for before ordering.
Are there multiple channels available in one housing?
Another way to control size is to have fiber links with multiple channels. In some cases, it is possible to have links with more than one channel. These links will still have only one fiber connection but allow multiple channels. This is a way to save on valuable test bench areas. An example of this is if you need to measure voltage on multiple points on a DUT, an analog unit with up to 16 channels can be used.
Are they compatible with your existing test setups?
Ease of use and integration into your test setup is important to reduce setup time and possible user errors. If each setup is the same, it helps with personnel training. For commonality, the same connectors and cabling are essential. Manufacturers can be accommodating to meet your needs. Understand, however, if changing a connector to a less shielded connector may have adverse effects on the unit’s overall EMI performance.
How long are the fiber optic cables provided?
Fiber cables will be provided with the system and may have distance limitations depending on the links. It is good to know and understand these limitations. If longer lengths are needed, always ask to make sure this is possible. It should not be assumed because it is a fiber connection, losses are low, and distance does not matter.
What support and maintenance services are available?
Having a support network available to answer and respond to you is very important. The links are used in a harsh environment, and issues will arise from time to time. Having local contacts is essential for fast response. A local technical contact is imperative to reduce downtime if products are manufactured internationally.
Camera systems
Camera systems have the same questions as above and some unique attributes that need to be addressed separately. A camera system consists of the camera, battery or power converter, optional Pan/Tilt, and a receiver for outs side the chamber. The receiver can have additional options for expanded use and control of the camera.
Are cameras optimized for low-light conditions?
Cameras used in an anechoic chamber must have a wide range of use. Lighting is not easily moved, added, and manipulated in a chamber, so the camera needs a wide working range for lighting. Low light capacity is an important requirement. With the rapid change in technology, read through your offer to see what specifications are included, which may differ from older data sheets. Operation and control of the iris may also be helpful when focusing on screens.
Is the camera resolution adequate for your needs?
Cameras can be offered in different Resolutions SD (standard definition), HD (High Definition), 4K, and even 8K. HD is more than adequate in most applications, giving amazing image quality and clarity. A higher resolution may only be needed to view other equally high-resolution screens.
Do you need pan/tilt capability?
Pan and tilt are useful for setting up and framing the DUT while you are outside the chamber. Without this, you will need manual adjustment inside the chamber and, if possible, a way to see the camera video inside the chamber. This is difficult as many cameras do not have a way to attach a screen directly to the camera. Having a handheld screen for the camera is a nice feature if manual pointing zooming is required. Without this, running in and out of the chamber to get the camera set correctly will quickly become tiresome. Using a pan/tilt function is highly recommended for this reason.
Does the camera have audio?
Cameras that offer audio can be very useful for hearing audio responses from DUTs, such as beeps and alarms. Not all camera systems offer audio. In this case, a separate system is needed to add to your overall cost.
What options do you need for the video receiver?
Receivers will be located at your workbench, where your testing is controlled. The receiver can offer many options. The basic receiver will have output to a monitor, allowing for control of the camera pan/tilt, zoom, Iris, and focus from the front panel.
Options:
- Adding a desktop joystick and remote control console may add some convenience.
- The ability to control the camera remotely through ethernet
- DVR
- Software interface, display frequency, time, and test information on the screen
- Computer streaming/capture
- Display of multiple cameras/screens on one monitor
- Stream video on ethernet and/or the internet
- ….
Do you need automated video-capturing software?
Screen capturing and screen monitoring are possible to automate your testing further. The software can see simple blinking lights or monitor dials, gauges, numbers, and text to see and respond to a failure to stop/report/or change testing. This capability must take the video data and digitally monitor it in real-time. This takes a lot of computer power to do this with HD video information and would take much more to do this in higher resolutions of 4K and 8K. This functionality is very useful in being more responsive them a test engineer.
EMI-shielded fiber optic links and cameras are revolutionizing EMC testing by ensuring accurate data transfer, real-time monitoring, and reliable analysis in the presence of electromagnetic interference. As electronic devices become more intricate and interconnected, the importance of EMC testing and EMI mitigation cannot be overstated. The integration of these advanced technologies paves the way for safer, more reliable, and compliant electronic systems that can thrive in our increasingly electrified world.
