App-26
IM 701240-01E
Computation Format (Resolution) of the Frequency Module
The computation flow on the frequency module is indicated below.
32-bit counter
A(Float)
Floating-
point
computa-
tion
Various
computa-
tions
Frequency
Period
....
D(Float)
E(Binary)
1 LSB weight
Range value
Value/Div
ACQ
Memory
Internally, all calculations
are performed using
floating-point.
2400 LSB/div
Binary Float
Float 16bit Binary
Computation (floating-point)
2400 LSB
/div
C(Float)
Offset value
Floating
point data
Input
50 ns resolution
The frequency module measures the period of the input signal using a 32-bit counter of
50-ns resolution. Therefore, the minimum resolution of the counter values is 50 ns.
Various computations are performed in floating point format. The data that is output from
the frequency module and written to the acquisition memory (ACQ Memory) is 16-bit
binary data. The data is converted using a weight of 1 LSB that is determined by Value/
div. The data is normalized to 2400 LSB/div when displayed on the screen.
Input: Conversion from the 32-bit Counter Value to Floating Point
Converts the count value obtained using the 32-bit counter with 50-ns resolution to
floating point format, and determines period A using the following equation.
Period: A (float) = (count value)
×
50 ns
Computation
Various computations are performed in floating point format based on the settings.
Example)
Frequency: C (float) = 1/A (float)
Calculation of the 1 LSB Weight of the Output
The 1 LSB weight of the output is determined from the range (Value/div).
Since 1 div = 2400 LSB,
1 LSB weight of the output = (Value/div)/2400
Computation Output: Conversion from Floating Point to 16-bit Binary
(When Offset Is 0)
When the offset value is 0, offset calculation is not performed, and C (float) = D (float).
The data is converted into 16-bit binary data and written to the acquisition memory (ACQ
Memory).
16-bit binary data: E (binary) = D (float)/(1 LSB weight of the output)
Offset Computation
When the offset value is not 0, the offset value is computed in floating point format using
the following equation and converted to 16-bit binary data.
D (float) = C (float) – offset value (float)
In offset computation, if the computed result C is equal to the offset value, the output is
0. If the computed result C (float) is less than the offset value, E (binary) is negative.
Appendix 11 Measurement Principles (Measurement Method and Update Rate) of the Frequency Module
