JPH0291579A - Frequency measuring method - Google Patents

Abstract

PURPOSE:To accurately measure a frequency for a range from a low frequency to a high frequency by executing a shift back for the value obtained from an 1/T calculation which is performed after shifting is carried out. CONSTITUTION:The number of clock signal is counted in accordance with the frequency cycle of a signal to be measured, and the counted value is stored in a memory with the specified number of bit as a binary signal. Next, the shift is made until the time when a leading bit of the counted binary value being stored is made to 1, and data for the specified number of high-order bits are taken-out from the value after the shift is carried out. Then, a reciprocal of the data taken-out is calculated and the correction is made to the obtained value in accordance with the number of the shift. The frequency measurement can be thereby made in the equivalent accuracy for the high and low frequency signals, and the sufficient measuring speed is obtained also for the low frequency signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a frequency measuring method, and particularly to a frequency measuring method that accurately measures a wide range of frequencies from low frequencies to high frequencies.

[Prior Art] Measuring the frequency of alternating current signals and the like has been conventionally performed. For example, in an automobile speedometer, etc., a magnet is attached to a rotating body, and the frequency of a pulse signal induced in a coil by the movement of the magnet is measured.

In such frequency measurements, when measuring slow frequencies, it is common to measure the time required for one cycle by counting clock signals, and convert this into a frequency. On the other hand, when measuring a fast frequency, the frequency is measured by counting the number of pulses that arrive within a certain period of time.

[Problems to be Solved by the Invention] According to such a conventional frequency n1 determination method, there are the following problems.

That is, the method of counting cycles has a problem in that as the frequency becomes faster, the numerical value of the count result for one cycle becomes a small value, and the error becomes large. Further, in the method of counting the number of pulses that have arrived within a certain period of time, there is a problem in that when the period becomes slow, the counting time must be increased, and the measurement takes time. Therefore, with conventional methods, it has not been possible to measure frequencies with high accuracy from low frequencies to high frequencies.

Purpose of the Invention The present invention was made to solve the above-mentioned problems, and an object of the present invention is to provide a frequency measurement method that can perform high-precision frequency measurements from low frequencies to high frequencies. .

[Means for Solving the Problems] The frequency measurement method according to the present invention includes a counting step of counting the number of clock signals in accordance with the period of the frequency of the signal under test, and a count value obtained in this counting step. a count value storage step in which a binary number signal is stored in a memory with a predetermined number of bits, a digit shift step in which the digits are shifted until the first bit of the stored binary count value becomes 1, and a numerical value after the digit shift. A calculation value extraction step in which a predetermined number of high-order bits of data are extracted from the data, a 1/T calculation step in which the reciprocal of the extracted data is calculated, and the above-mentioned digit shift for the numerical value obtained in this 1/T calculation step. It is characterized in that it has a digit return step that performs correction corresponding to the number of digits shifted in the process, and can perform frequency measurement with the same precision for high frequency signals and low frequency signals.

[Operation] The frequency measuring method according to the present invention has the above-mentioned configuration, and after performing digit movement, performs 1/T calculation, and performs digit reversal on this calculated value. Therefore, the same 1/T calculation of significant figures can be performed for both signals with a slow period and signals with a fast period. Therefore, frequency measurement can be performed with similar precision for signals with a fast period to signals with a slow period.

[Embodiment 1] A frequency measuring method according to an embodiment of the present invention will be described below with reference to the drawings.

For example, the signal to be measured Fin, which is a pulse signal related to the rotational speed of a car, is input to a counter, and one cycle is counted here. In this example, one is added each time a clock signal is input, and this added value is stored. Since this counter consists of a 20-bit memory element, θ
Values from ~1.048,575 can be stored. Therefore,
A clock signal of 1,000,000 Hz is used, and the frequency of the input signal under test F1n is 1 to 1.
If it is 250H2, change this to 1,000,00
It can be counted as a value between 0 and 4.000.

Next, determine whether the most significant value of the counter value, that is, the value of the 20th bit, is 0 (Is the first bit O?)
. That is, if the count value is smaller than 2 to the 19th power, the 20th bit is 0.

Then, if the value of the first bit is O, digit movement is performed for the value obtained by the counter (binary digit movement).

This digit shift is performed by moving the stored contents one by one to the right for the binary count value stored in the 20-bit counter until the first bit becomes 1.

That is, when a count value is stored from the left of a 20-bit storage element, it is determined whether the content of the rightmost storage element (first bit) is 0 or 1, and if it is 0,
Moves the memory contents one by one to the right. This right feed is performed by adding O's one by one from the left, for example by multiplying by 2.

Then, repeat until the value of this first bit becomes 1,
The number of times of this movement is memorized (movement digit memory). In this example, the count value on the counter is 4,0.
Since it is about 00 to t, ooo, ooo, the number of movements is 7
The digit shift will be performed ~θ times.

When the first bit becomes 1, a predetermined number of data starting from the first bit are stored in a memory that stores calculated values. For example, by supplying data to an 8-bit memory, 8 bits of data starting from the first bit are stored here.

Then, the reciprocal is calculated for this 8-bit data (1/T calculation).

Next, for this calculated data, a digit return corresponding to the moved digit is performed (binary digit return). That is, in the above-mentioned digit shift, if N digits were shifted by multiplying 2 N times, the predetermined digit return is performed by multiplying 2 to the N power of the data after the calculation. .

This calculation can be explained using a formula as follows.

That is, the count value is X and the clock signal is I.
If it is MHz, the period at that time is period - x / IMH
It is z.

However, in the method of this invention, digits are shifted by multiplying 2 to the N power, so the period T after digit shifting is
becomes T-x/IMHz x2N.

When a 1/T operation is performed on this, the frequency F is calculated as follows.

F-1/T-IMHz/2N-x Then, by multiplying the obtained F by 2N, frequency = 1
/T-1/x MHz, and it is understood that the frequency is obtained.

In this way, the frequency can be measured from the count value in the counter. In this embodiment, a clock pulse with a fairly fast cycle, ie, 1,000.000 Hz, is used.

Therefore, the count value is 4,000 even for a signal with a frequency of 250 Hz. Here, this count value 4
．． 000 corresponds to approximately 2 to the 12th power.

The data actually used for the 1/T operation is 8-bit data, and the operation is performed in binary with 8 significant digits. In this way, frequency measurement can be performed with sufficient accuracy even for signals with a frequency of 250 Hz.

Furthermore, in this embodiment, depending on the size of the data to be subjected to the 1/T operation, the significant figures are 2/12 in binary.
It can be set arbitrarily up to the second power. Note that since 2 to the 8th power is 256, the 8 significant digits in the binary number correspond to the significant digits between the 3rd and 4th digits in the decimal number.

On the other hand, for a slow-cycle signal with a frequency of IHz, the count value is 1,000,000, and if this is calculated as is, a large work area is required and the calculation time becomes long. However, according to this embodiment, only eight binary digits are subjected to the 1/T operation. Therefore, frequency measurement can be performed with the same accuracy as the frequency measurement of 250 Hz, unnecessary high-precision calculations can be omitted, and frequency measurement can be performed with desired accuracy.

[Effects of the Invention] As explained below, according to the frequency measurement method according to the present invention, measurements can be made with the same accuracy from low frequencies to high frequencies. Furthermore, the measurement speed can be made sufficient even for low frequency signals.

[Brief explanation of the drawing]

FIG. 1 is a flowchart of a frequency measurement method according to the present invention.

Claims (1)

[Claims] (1) A counting step in which the number of clock signals is counted according to the period of the frequency of the signal under test, and the count value obtained in this counting step is stored in a memory of a predetermined number of bits.
A count value storage step in which the count value is stored as a base number signal, a digit shift step in which the digits are shifted until the first bit of the stored binary count value becomes 1, and a predetermined number of upper bits of data are extracted from the value after the digit shift. A calculation value extraction step to extract the calculated value, a 1/T calculation step to calculate the reciprocal of the retrieved data, and a 1/T calculation step to calculate the number of digits shifted in the digit shift step for the numerical value obtained in this 1/T calculation step. 1. A frequency measurement method, comprising: a digit return step for performing corresponding correction, and is capable of performing frequency measurements with similar precision for high-frequency signals and low-frequency signals.