JPS6025746B2 - Frequency anomaly detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a frequency abnormality detector that detects minute changes in frequency due to deterioration in frequency stability of, for example, a highly stable crystal oscillator.

Conventional methods for detecting frequency abnormalities include (a) detecting abnormalities by direct measurement using a frequency counter with sufficient measurement accuracy;

{b' A reference frequency with sufficient frequency accuracy is divided or multiplied to match the frequency to be measured, and a phase comparator detects a frequency deviation as a phase fluctuation.

etc. were common methods.

However, their method had the following drawbacks.

A frequency counter with sufficient measurement accuracy is required as an 'a' measuring device, and the accuracy of the reference frequency oscillator in the frequency counter must be considerably higher than that of the highly stable oscillator to be detected. The disadvantage of conventional frequency counters is that they are very expensive.

[b--In order to detect phase fluctuations using a phase comparator, a highly stable reference oscillator whose frequency matches that of the frequency to be detected is required, which has the drawback of being difficult to obtain.

This invention provides a frequency anomaly detector that detects an abnormality in the frequency of an oscillator of any frequency by using reference frequencies such as IMHZ, 8MHZ, mother MHZ, and 10MH2, which are conventionally commonly used as frequency reference signals. The purpose is to obtain.

FIG. 1 is a block wiring diagram showing an embodiment of the present invention, in which 1 is an input terminal for the reference frequency ■, 2 is a frequency to be measured f
3 is a digital mixer that mixes the measured frequency input and the input from the reference frequency input terminal 1 and outputs the beat frequency fb; 4 is a digital mixer that mixes the frequency input to be measured with the input from the reference frequency input terminal 1; count (a, is any positive integer), t, time (t, =
a,/f.

), 5 is a frequency counter that generates a trigger output at the trigger output of this frequency counter from L to a2 times (a2 is any positive integer) input of the reference frequency (t2 = a2
/f. ), 6 is a window generating circuit which outputs a window signal with a width up to b.
A beat frequency counter (b is a positive integer) counts and generates a trigger output during the window signal, and 7 detects a frequency abnormality from the trigger output from this beat frequency counter and the output of the window generation circuit 5. A flip-flop circuit, 8 is an output terminal of this flip-flop circuit. In the frequency abnormality detector configured as described above, the input/output characteristics of the digital mixer 3 are as shown in FIG.

FIG. 2 is an input/output characteristic diagram of the digital mixer 3. If this relationship is expressed numerically, it will be '1', formula ■. fbi
lf-nfoI n' positive integer ... [1) f
bSfo/2 ... [2] Now, suppose f = k, k' or any magnification factor n...
・If (3} is '1}, from the side equation fb=lkfo-
nth place l=folk-nl...[4'n is any positive integer, so even if k is a very large value, lk
-nl is a very small number of 0.5 or less.

For example, = IMHZ, f = 130.01MHZ, n = 1
If 30k=130.01, fbni foil3
0.01 - 130l = 0.01 one frequency counter 4
When the trigger output is generated, t,=a,/fo, the window generating circuit 5 generates a window signal between 1 and 2 as shown in FIG.

FIG. 3 is a time chart of the frequency abnormality detector shown in FIG.

The beat frequency counter 6 receives the output f of the digital mixer 3.
b is counted b times, and the trigger output generated during the window signal is as shown in FIG. 3c.

This trigger output and the output of the window generator 5 are compared in a flip-flop circuit 7, and since the count number b is fixed, if the trigger output of the beat frequency counter 6 is within the width of the window signal, it is normal and the window signal is out of range. If so, an alarm is issued from the output terminal 8 as an abnormal signal. Note that for time synchronization, the frequency counter 4 and the beat frequency counter 6 are reset by the trigger output of the beat frequency counter 6. The above relationship can be expressed as a k'-order equation when there is a variation Δf in f.

f+△f=k'f k'==k+△k △k=△f/f...{51 Also, the beat frequency is as shown in the following equation.

rb=folK-nlni&lk+△k-nl =lk-nlb+l△klfo...'61 That is, the fluctuation in the beat frequency is expressed as a platform, and is 33 times larger than the fluctuation in the constant frequency △k on the sensitive side. It means it's gotten bigger.

Using the numerical example above to find this value, k=130.0
Since 1n = 130, k 130.01 k - n 130.01 - 130 = 13001 This means that the time of the trigger output, which was generated by counting the beat frequency b exposed during normal operation, is due to the fluctuation △f in the frequency f. In some cases, the deviation will be large and the tolerance range will be exceeded.

Also, the fact that the variation in beat frequency appears large is t, ~
It becomes possible to ignore the setting error of t2. Examining this relationship using the above numerical example, since fo=IMHZ, the setting accuracy of t2 is 1/b=±1 ms.

If △k/k = 10-8, the variation in the number of beat jobs is Gaku x 33 = ・o-8xl. 3001×1 pi=1.300
Even if 1×10-4chi=1 second, the error of 1 ms is 1.30
This value is sufficiently negligible compared to 01×10-4.

In this way, the frequency fluctuation is greatly expanded by the beat frequency, exceeds the width of the wind wave, and is detected as an abnormal frequency fluctuation.

Further, although the window generating circuit 5 uses the reference frequency fo to accurately define its width, a certain degree of setting error is allowed, so that it can be put to practical use even as a one-shot multi-circuit or the like.

Furthermore, by detecting the trigger output of the beat frequency counter 6 before and after the window signal, it is possible to easily determine whether the frequency is high or low.

Although the above embodiment has been described for frequency abnormality detection, it can also be used for frequency correction by appropriately narrowing the width t2 of the wind signal.

As described above, the present invention has the advantage that highly accurate frequency abnormality detection can be performed with a simple configuration without using an expensive high-precision frequency counter or continuous recording device such as a pen recorder.

[Brief Description of the Drawings] Fig. 1 is a block diagram showing one embodiment of the present invention, Fig. 2 is an input/output characteristic diagram of a digital mixer, and Fig. 3 is a diagram showing an input/output characteristic of a digital mixer.
3 is a time chart of the frequency abnormality detector shown in FIG. In the figure, 1 is an input terminal for the reference frequency, 2 is an input terminal for the measured frequency f, 3 is a digital mixer, 4 is a frequency counter, 5 is a window generator, 6 is a beat frequency counter, and 7 is a flip-flop circuit. . Note that the same reference numerals in each figure indicate the same or corresponding parts. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. A reference frequency input that serves as a reference for measurement, a frequency counter that counts a_1 of this reference frequency input (a_1 is a positive integer) and generates a trigger output, and a_2 of the above reference frequency input from the time of trigger output of this frequency counter. (a_2 is a positive integer) A window generator that outputs a window signal with a width of A frequency abnormality detector comprising: a beat frequency counter that generates an output; and a detection circuit that detects whether a trigger output of the beat frequency counter falls within the width of the window signal.