Frequently Asked Questions
Miscellaneous / Frequency Counters/Analyzers
- Why do my input settings seem to get overridden when I initiate a measurement with the :MEAS? command?
The :MEAS? command is primarily intended for making programming easier and is a compound command that tries to optimize miscellaneous settings for the given function, for example :MEAS:PER?, before starting the actual measurement and reading the result. Consequently it can change earlier settings, so if you want to have total control over the counter, you can use the :CONF command instead and make the desired adjustments of input settings between this command and READ?
CNT-91 Timer/Counter/Analyzer / Frequency Counters/Analyzers
- When the frequency ratio measurement is conducted with the CNT-91, the number of digits for the measurement results decreases compared to that in the frequency measurement. Why is it?
A normal frequency measurement is performed during a set measuring time, eg 100 ms (default setting), giving typically 11 digits resolution ("smart" frequency calculation).
A frequency ratio A/B is performed as a standard ("non-smart") Freq(A) measurement during a measuring time that equals 1 period of the input B signal. The normal measurement time seting is not used in Freq Ratio measurements, measurement time is always one period of input B signal.
The resolution of the Freq ratio is less than a normal Freq(A) measurement for two reasons.
- A - The measurement time is typically short (1 period of input B signal)
- B - The measurement is not "smart", i,e, is not using statistical improvement of resolution
Like any measurement function, the resolution of frequency ratio measurements can be increased by using the built-in statistics mean value feature. As the improvement is proportional to the square root of the number of samples, you should expect one more digit with100 samples and two more digits with 10000 samples. The cost is time of course. - The number of figures displayed was five at a maximum when we investigate the symptom at our facility. Is there any function to increase the number of digits for the frequency ratio measurement?
5 digits indicate a measuring time in the order of 0.1 to 1 us, or an input B frequency of 1 to 10 MHz. The only way to improve the number of digits in ratio is to use a lower input B frequency (longer period and thus also longer measurement time) if possible.
