Pendulum Instruments · Frequency and Time Interval Analyzers
CNT-91/91R
High-resolution timer/counter/analyzer for calibration labs and R&D benches
The CNT-91 is the model in this line that calibration labs pick most often, and the reason is usually its time resolution: 35 ps time stamping and 50 ps single-shot time interval, combined with 250,000 measurements per second and up to 3.75 million results in internal memory, so jitter and time interval statistics can be finished on the instrument itself. The 91R version adds a built-in rubidium timebase for sites with no external reference to connect. The standard frequency range is 0.002 Hz to 400 MHz, and an optional third input extends it to 3, 8, 15 or 20 GHz. The two decisions to make at order time are whether you need the rubidium timebase of the R version, and the ceiling of the third input.
Overview
In jitter and time interval work the sample count largely decides how much a conclusion is worth: ten readings show nothing about a distribution, a hundred thousand do. The CNT-91 is built around that fact. The 35 ps time-stamping resolution makes each individual reading trustworthy, 250,000 measurements per second gather enough samples in a reasonable time, and 3.75 million results of internal memory keep the whole record in the instrument until it is analyzed, with no need to stream it out live. Display resolution reaches 14 digits and frequency resolution is 12 digits per second. The 91R differs in its timebase: a built-in rubidium oscillator holds the rated uncertainty where no external 10 MHz is available, which settles the choice for field calibration or a temporary measurement station. With TimeView software the counter works as a modulation domain analyzer and plots frequency against time. In practice the same unit often serves as both a calibration working standard and an R&D measuring instrument. Evencat is the authorized distributor for Pendulum Instruments in Taiwan and quotes the CNT-91 and CNT-91R with options and calibration.
Key specifications
| Standard frequency range | 0.002 Hz to 400 MHz (2 channels) |
|---|---|
| Optional frequency extension | 3 GHz, 8 GHz, 15 GHz (Option 14) or 20 GHz (third-channel options) |
| Time resolution (single shot) | 50 ps (single-shot time interval); time-stamping resolution 35 ps |
| Frequency resolution | 12 digits/s; display up to 14 digits |
| Measurement rate | 250,000 measurements/s; internal memory holds up to 3.75M results |
| GPIB bus transfer rate | 15,000 results/s (block mode); 4,000 results/s (talker only) |
| Input impedance | 1 MΩ ∥ 20 pF or 50 Ω (switchable) |
| Input sensitivity | 15 mVrms (DC to 200 MHz); 35 mVrms (300 to 400 MHz) |
| Timebase options (CNT-91) | OCXO 0.06 ppm/month (19/90), 0.01 ppm/month (30/90) or 0.003 ppm/month (40/90) |
| Timebase (CNT-91R) | Built-in ultra-stable rubidium atomic oscillator |
| Programmable pulse output | 0.5 Hz to 50 MHz |
| Dimensions / weight | 210 × 90 × 395 mm (W × H × D) / net 2.7 kg |
| Power supply | 100 to 240 Vac, 50 to 400 Hz |
Features
35 ps time-stamping resolution
Each timestamp is accurate on its own, so the noise floor in a jitter analysis comes from the device under test, not the counter.
Enough samples for real statistics
250,000 readings per second and 3.75 million results of memory reveal the distribution and the outliers, not just the mean.
Rubidium timebase in the R version
Holds the rated uncertainty where no external 10 MHz reference is available, which suits field calibration.
Microwave extension
The optional third input reaches 3, 8, 15 or 20 GHz, so one counter covers both baseband and microwave devices.
Upgradable to modulation domain analysis
With TimeView you see the frequency trajectory over time rather than a list of individual readings.
Complete interfaces
USB and GPIB (IEEE 488.2 / SCPI) are standard, and GPIB block mode transfers up to 15,000 results per second, so fast captures do not stall at the interface.
Typical applications
Oscillator development
PLL and oscillator jitter characterization
Engineers designing OCXOs, rubidium references or PLL synthesizers use the modulation domain analysis of the CNT-91 with TimeView to capture small frequency drifts as continuous, zero-dead-time measurements at 250,000 readings per second. Histogram and trend views show the whole behavior from slow drift to fast jitter, replacing a combined oscilloscope and spectrum analyzer workflow.
Automated test
High-speed frequency verification on ATE lines
In electronics production ATE the CNT-91 streams results to the host over GPIB in block mode and offers a 53131/53132 compatible mode, so existing test programs carry over without a rewrite. Batch verification of frequency, period, pulse width and rise time gains throughput as a result.
Frequency calibration
CNT-91R portable field frequency calibration
With its built-in ultra-stable rubidium atomic timebase, typical total uncertainty better than 2.5×10⁻¹⁰ one year after calibration, the CNT-91R needs no external frequency standard, so calibration staff can carry it to base station master oscillators, satellite ground station equipment or avionics and verify frequency on site. The graphic display guides the adjustment live and shortens the time spent trimming a source.
Options and configuration
Tick the options you need. We compile the configuration list and carry it into the quote request form.
Standard configuration (included)
Hardware options
Software, calibration and warranty options
Downloads
- Product datasheetCNT-91 & CNT-91R Datasheet · PDF
- User manualCNT-90 Series User Manual · PDF
- Programmer's handbookCNT-90 Series Programmer's Handbook · PDF
- Application note: introduction to modulation domain analysisApplication Note · PDF
- White paper: continuous zero-dead-time measurementWhite Paper · PDF
- Manufacturer product pagependulum-instruments.com
Need pricing, specifications or lead time for CNT-91-91R?
Also available for rent: CNT-91-91R is part of the Pendulum rental program, for project peaks, calibration backup and pre-purchase trials. Rental inquiry →