- Time Domain Scan Reduces Overall Test Time, 10 Hours vs 12 Min., 50 times faster.
Electromagnetic compatibility (EMC) testing requires detailed and exacting methodologies to ensure that all emissions are accurately measured.
Long test times impact our test facility availability and reduce the number of devices that can be certified.
To grow revenue without adding the considerable expense of new test site installations, companies must streamline the EMC product test cycle—which includes setup, scan, turntable rotation, and antenna height adjustment time—to maximize the throughput of our existing compliance facilities.
Time domain scan is a technology that can reduce receiver scan time significantly, shortening overall test time to help increase revenue and introduce more products to market faster.
Both commercial and military testing standards require specific amounts of measurement time, also known as dwell time, for each signal in order to ensure that impulsive signals are appropriately characterized. Time domain scan reduces receiver scan time while maintaining required dwell times.
CISPR-based commercial testing can require dwell times up to 1 second for pre-scans and, in the case of emissions with time-varying amplitudes, 15 seconds or more for final measurements. MIL-STD-461 specifies dwell times of between 15 ms and 150 ms per measurement, depending on the frequency range. These dwell times add up when using receivers that employ frequency domain scanning based on stepped or swept local oscillators to collect data in individual resolution bandwidths.
Time domain scanning provides significant time savings during pre-scan (the collection of suspect signals prior to final measurement) because it is during this process where the receiver tunes through the entire measurement band. For example, when collecting suspect frequencies according to methodologies required in CISPR 16-2-3: 2010, ed. 3.1, section 7.6.6, a sweep should be made for every 15 degrees of turntable rotation and for both polarizations of the receive antenna (total of 48 receiver scans). In addition, antenna height scanning may be required. For this discussion, we will say that measurements for 3 heights will be made at each azimuth for each polarization, for a total of 144 receiver scans.
To measure emissions in the 30 MHz to 1 GHz range, the suspect list is created by pre-scanning with a peak detector, 4 measurement points for every resolution bandwidth (in this example, every 30 kHz for a 120 kHz CISPR resolution bandwidth), and a 10 ms dwell time for each point. In the frequency domain, commercially available receivers make this scan in approximately 250 seconds, which would result in a total pre-scanning time of approximately 10 hours!
For example, using time domain scan, our new receiver can make this same scan in about 12 seconds, reducing the total scan time to just under 30 minutes—a significant time savings. Note that in both scenarios, the total associated turntable and antenna movement time required to collect these 144 scans is approximately 12 minutes.
- Benefits of Digital IF
With today’s accelerating business environment and development cycles, EMC measurement facilities that offer rapid test turnaround and high throughput, while still providing accurate and reliable measurements, will achieve greater success of Client(s).
Modern EMI receivers and spectrum analyzers used for compliance and pre-compliance testing employ digital intermediate-frequency processing technology (digital IF) for signal analysis. Not only does digital IF boost overall instrument reliability, it enables improved amplitude accuracy, increased measurement throughput, and reduced dependence on operator experience level. These benefits result in higher efficiency and lower operating costs.
Improved instrument amplitude accuracy
The enhanced accuracy provided by digital IF results in more precise amplitude specifications for receivers and spectrum analyzers. Not only can you make more accurate measurements, client benefits from this improved accuracy over a broader range of instrument settings. The digitally-implemented log correction provides increased measurement accuracy for very low level signals. This is important in an EMC measurement environment because low signal levels are encountered on a regular basis when making compliance measurements.
Improved measurement throughput
One measurement technique EMC laboratories have adopted to minimize the effects of errors associated with analog IF log amplification is to always bring the peak signal to the reference level prior to final quasi-peak or average detector measurement. This technique brings the IF level to the top of the current reference level setting, which eliminates the log display error. While effective, this measurement technique takes time because it has to be done on every signal. Automation software can reduce the time impact, but the measurements must still be done on every signal. The total time savings is a function of the number of signals being measured.
The enhanced accuracy of the digitally-implemented log correction minimizes the need to adjust each signal to the measurement reference level prior to final measurement. This is a considerable time savings when testing devices with a significant number of emissions.
Improved ability to identify low-level emissions in a high-ambient environment
When making compliance or pre-compliance emissions measurements on an open site, it can be difficult to resolve low-level emissions in the presence of high-level ambient signals, such as commercial radio and television broadcasts, cellular transmissions, and public safety communications.
The tighter shape factors offered by digital IF resolution bandwidths allow you to resolve and identify emissions that are located closer to ambient signals. Accurately identifying and measuring these signals reduces the chance that hidden signals will cause a surprise failure at a final measurement in a shielded environment. This capability is very important for pre-compliance measurements, which are typically made in an open-air environment.