Omega OMB-DAQBOARD-3000 Series User Manual page 58

Upper 16-bits of the 32-bit counter
Range (Hz)
15u – 1500u
150u – 15m
1500u – 150m
15m – 1500m
150m – 15
1500m – 150
15 – 1500
Each frequency range given in the previous table-set can be exceded. If the input waveform goes under-
range by too much, the counter value will top out at 65535 indicating you have reached the lowest possible
frequency that can be measured on that range. If the input waveform goes over range by too much, the
counter will return values that are very course and have a lot of sampling error. The values returned will
have a small number of counts for the period duration. If an input waveform cannot fit within one of the
16-bit ranges shown above or requires much higher accuracy, then a 32-bit range should be considered.
Full 32-bit Counter
Range (Hz)
15u – 100
150u – 1k
1.5m – 10k
15m – 100k
150m – 1M
1.5 – 5M
15 – 5M
The 32-bit ranges shown above are much wider than the 16-bit ranges, but also require the full 32-bit value
to be returned. Since digital or counter channels do not take up any time in the scan period there is no
disadvantage in reading a 32-bit counter versus a 16-bit counter. The 32-bit frequency ranges can also be
exceeded with a loss of accuracy or topping out at 4,294,967,295 counts.
Some measurements will require the accuracy of an input waveform to be free of sampling error, having only
the absolute accuracy of the internal timebase as the source of error. Sampling error can be averaged out to
give the required result. In most cases, the 3000 Series board can perform the required averaging on the
values before they are returned to the PC. The frequency ranges shown below will give a sampling error
that is less than 10ppm or 1ppm.
Full 32-bit Counter <10 ppm
Range (Hz)
15u – 500m
150u – 5
1.5m – 50
15m – 500
150m – 5k
1.5 – 50k
15 – 500k
If the input frequency is required to have less than 1 ppm sampling error and is greater than 50kHz, use the
15– 50kHz, 1ppm range. The values returned will have sampling error that is greater than 1ppm but they
can be averaged by the PC software to further reduce the sampling error.
5-10 Counter Input Modes
Ticksize (nS) Averaging
Option
20833.333
2083.333
208.333
20.833
20.833 10
20.833 100
20.833 1000
Frequency Ranges for a 16-bit value, sampling error is less than 0.21%
Ticksize (nS)
20833.333
2083.333
208.333
20.833
20.833
20.833
20.833
Frequency Ranges for a 32-bit Value,
Sampling Error is Less than 0.21%
Ticksize (nS) Averaging
Option
20833.333
2083.333
208.333
20.833
20.833
20.833 100
20.833 1000
High Accuracy Frequency Ranges for a 32-bit Value
that has little sampling error (<10ppm, <1ppm)
918494
Lower 16-bits of the 32-bit counter
Range (Hz)
1 1 – 100
1 10 – 1k
1 100 – 10k
1 1k – 100k
10k – 1M
100k – 5M
1M – 5M
Averaging Option
1
1
1
1
10
100
1000
Full 32-bit Counter <1 ppm
Range (Hz)
1 15u – 50m
1 150u – 500m
1 1.5m – 5
1 15m – 50
10 150m – 500
1.5 – 5k
15 – 50k
Ticksize (nS) Averaging
Option
20833.333 1
2083.333 1
208.333 1
20.833 1
20.833 10
20.833 100
20.833 1000
Ticksize (nS) Averaging
Option
20833.333 1
2083.333 1
208.333 1
20.833 1
20.833 10
20.833 100
20.833 1000
DaqBoard/3000 Series User's Manual