Here's news of a neat high-res frequency counter that's operable in either an IEEE-488/GPIB instrumentation environment, or across a Universal Serial Bus (USB) connection. Pendulum Instruments AB's (Bromma, Sweden) new CNT-90 timer/counter/analyzer can measure frequency, time interval, and phase. You can make 2,000 individual triggered measurements/s via either GPIB or USB.
Its basic frequency range extends to 300 MHz, but 3 GHz, 8 GHz, and even 14 GHz microwave options are available. What's more---and what's interesting---is that this instrument offers two more digits than competing interpolating counters.
The CNT-90 is also a plug-and-play box that can be readily added to existing test systems, thanks to an Agilent 53131A emulation mode (the 53131A offers frequency resolution of 10 digits/s, with a 500-ps time interval resolution; it includes two 225-MHz channels, however there's an optional third channel available that can measure up to 3 GHz, 5 GHz, or 12.4 GHz).
The plug-and-play capability means you can likely use a CNT-90 for most microwave measurements---without having to buy separate instruments. Also, the CNT-90's plug-and-play ability reduces the need to re-program existing system commands in scripts you may have already crafted.
The GPIB interface also comes in two modes: SCPI/1999 (Standard Commands For Programmable Instruments) and the 53131A emulation mode. This almost-instant plug-and-play feature also reduces the need to re-program.
Useful in test systems, on the bench, in the cal lab, or out in the field, Pendulum's new CNT-90 also offers a very fast speed of 250,000 measurements/s, with a resolution of 12 digits/s.
The CNT-90 also touts a high accuracy ovenized crystal-controlled timebase, and there are higher stability timebase options available that will take you out to 0.003-ppm/month specs. That kind of stability can ensure extremely low time-interval A-B errors, to say the least.
A Graphical Interface
The system's graphical user interface (GUI) is also nifty. It displays distribution histograms, trends, and modulation domain, in addition to numerical multi-parameter displays with up to 14 digits of resolution. That can resolve to 100-ps of time, 12 digits/s for frequency, and 0.001° of phase.
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The graphical presentation of results (as histograms, trends, or modulation, for example) can give a human understanding of random signal distribution and measurement changes over time, from slow drift to fast jitter and modulation. In use, the unit's fast measurement speed to internal memory, and its memory depth, also makes modulation domain analysis possible by capturing very fast frequency changes in realtime.
This instrument can also write measurements to internal memory, with the ability to store up to 750,000 measurement results. This is aided by the CNT-90's ability to auto-trigger. The automatic triggering sets optimum trigger levels and hysteresis that's adapted to an actual input signal.
The CNT-90 also touts a number of trigger functions, such as arming, adjustable arming delay, trigger hold-off, and limit qualifying. Arming enables full control of both start and stop points of time or frequency measurements. Frequency burst parameters can also be automatically detected due to the adjustable arming delay and trigger hold-off, both with 10-ns resolution.
Pendulum's system also uses a so-called zero dead-time technique, as well as and continuous time-stamping of trigger events. Fast time-stamping of trigger events enables capture of all individual periods, back-to-back without dead-time, at up to 250,000 measurements/s.
This feature is valuable in mechanical systems where you might use it to make rotary encoder tests, for example, or for medical applications such as nerve impulse or respiratory cycle measurements.
The CNT-90 also performs time-interval measurements using a single-pass technique. Unlike approaches where you need to define start and stop channels beforehand, you can now let the CNT-90 detect Start and Stop automatically. That eliminates false results due to a Stop signal occurring before a Start signal.
This counter box can also make true phase and duty cycle measurements, also using a single-pass technique. You can even measure phase measurements between signals with varying frequency. That's a feature that can be used to verify the relative phase between quadrature output pulses from devices such as rotational encoders, where rotation speed can vary during the measurement.
The CNT-90 also uses something called measurement pacing. It's a technique that sets an accurate sample rate for a measurement, ensuring that samples are taken at exact and equidistant intervals.
The instrument also offers hysteresis compensation. When making time-interval measurements, hysteresis comp can reduce trigger level errors. Pendulum claims a 2.5-mV error, as opposed to the typical 15-mV to 20-mV errors of competing counters. The company also points out that that's a 6X to 8X improvement in trigger precision for critical time-interval measurements.
Operationally, the CNT-90 includes a menu-oriented settings interface in addition to the aforementioned GUI. Signal information is displayed with up to 14 digits for auxiliary parameters. The latter often sidesteps the need for additional instruments such as digital voltmeters or oscilloscopes that are typically called into play in many time measurement and frequency measurement applications.
The box also gives you so-called limit qualifying. It lets you accept or reject measurement values at pre-set limits, a feature that can come in handy when performing calculations of statistical parameters. It can be used, for example, to verify rms jitter of digital pulses that appear in discrete clusters. Setting limits lets you isolate one cluster in a calculation.
For lots more info, contact Pendulum Instruments AB, Karlsbodavgen 39, Box 20020, SE-161 02 Bromma, Sweden. Phone: +46 8-598 510 00. Fax: +46 8-598 510 40. E-mail: email@example.com
Or, visit Pendulum's Web site.