FV Converter Frequently Asked Questions

The approximate resolution of FV conversion is shown in the table below.

Let's explain using 1500 Hz as an example.

The clock used for period measurement is 20 MHz. The count value for the input frequency is:

20,000,000 ÷ (Input frequency) = Count value

At 1500Hz, 20,000,000 ÷ 1500 = 13333.33

Since the count value is an integer, the resolution will be either 13333 or 13334. If we work backwards from this count value to calculate the frequency:

20000000÷13333＝1500.0375
20000000÷13334＝1499.925

The difference is 1500.0375 - 1499.925 = 0.1125 Hz

Therefore, it can be said that there is a resolution of approximately 0.12 Hz around 1500 Hz. However, there is something to note here: there is an error of 0.0375 Hz in the measurement of 1500 Hz. When the accuracy of the crystal oscillator is taken into account, the accuracy becomes 0.12 Hz plus a little extra.

- In the case of deviation output

Even with deviation output, the resolution remains the same, but the output voltage per resolution unit can be significantly higher.

• Low-frequency accuracy

The reciprocal of the count value is converted to a voltage using a 16-bit DA converter and output.
The frequency at which the count value becomes fully 16 bits is 305.1 Hz.
At low frequencies below 305.1 Hz, the number of bits required is 16 or more, so the lower digit of the binary counter is cut off, and calculations are performed using the upper 16 digits.
Therefore, the accuracy in this case is:

Accuracy = Input frequency ÷ 2 ¹⁵

This is what it will be.

- Accuracy as stated in the catalog

Voltage output 0.1% FS
Current output 0.7% FS

The accuracy is worst at 20 kHz, so the resolution plus the analog circuit accuracy at this frequency is listed.

The input frequency can be modified to a maximum of 50 kHz. The same considerations apply to resolution in this case as well.