CF-5200 Frequently Asked Questions

During rotation tracking, data is sampled while monitoring the rotation. In the CF−5200, the timing for checking the rotation is set to once per rotation. In contrast, for the CF−840, the timing is set to four times per rotation. (The timing changes according to the division ratio, which is automatically adjusted based on the number of input pulses per rotation)
At the current rotation speed (approximately 100 r/min), 3 seconds corresponds to about 6 rotations. Therefore, it is believed that the difference in the number of measurement points, as seen this time, is due to the timing.

The measurable rotation range is

The specifications of CF−840 state that the rotational lower limit is 50 r/min.

The specifications of the CF5200 state that the rotational lower limit is 20 r/min.

It is.

Please note that the data is valid within the measurement range. Additionally, due to the relationship with sampling time, it is necessary to make changes in rotational speed slowly in the low rotation range. To confirm whether the rotational rise time is appropriate, display the frequency spectrum and monitor the situation during the rotational increase. If the spectrum shows a distorted waveform, it should be judged as too early.

As mentioned above, the CF5200 calculates rotational speed based on a timing of one pulse per rotation. At low rotational speeds, the interval between pulses becomes longer, resulting in a delayed recognition of changes in rotational speed. If there are many pulses per rotation, there are methods to avoid this issue, which can be used in cases of fixed width, frequency, and octave tracking.

operating method

For example, if we consider a rotation pulse of 60 P/R;

N PULSE／R → 1

REVDIVDE FACT → 60

With the above settings, it is possible to capture approximately 60 points in 3 seconds at speeds ranging from 20r/min to 200r/min.

The sampling frequency is as follows.

• Setting times: M

• Set rotation pulse count: P

• Number of pulses per rotation: Let it be P0.

Number of samples per rotation = (P0) ÷ P × M × 2.56

If P0 = 60, P = 60, and M = 25, then the number of samples per rotation is 64.

This requires a sampling frequency of more than twice that of the analytical signal according to the sampling theorem. In CF, it is set to 2.56 times.

The highest frequency of the analysis signal is expressed as 25th order, which can be represented in frequency as rotational speed R, thus 25×R (Hz). The sampling frequency is 25×R×2.56=64×R.
Since R is incorporated into CF as P0, it can automatically generate the sampling frequency internally.