CN202119834U

CN202119834U - Frequency measurement circuit of equal precision

Info

Publication number: CN202119834U
Application number: CN201020695393XU
Authority: CN
Inventors: 朱强; 韩媛; 高雪丽; 山陈琦
Original assignee: Shanghai Automation Instrumentation Co Ltd
Current assignee: Shanghai instrument and meter for automation company limited
Priority date: 2010-12-30
Filing date: 2010-12-30
Publication date: 2012-01-18
Anticipated expiration: 2020-12-30

Abstract

The utility model discloses a frequency measurement circuit of equal precision, comprising a first counter, a second counter and a frequency division counter. A detected signal is respectively connected with clock input ends of a first D trigger and a second D trigger; a trigger end of the first D trigger is connected with a control signal START; an output end of the first D trigger is connected with an enable end of the first counter; a trigger end of the second D trigger is connected with a control signal STOP; an output end of the second D trigger is connected with an enable end of the second counter; thus synchronization control of rising edges of the control signal and the detected signal is realized; an output signal of the frequency division counter is connected with a clock input end of the first counter; and the detected signal is connected with a clock input end of the second counter. The frequency measurement circuit of equal precision provided by the utility model eliminates an error of pulse signal number brought by a counting method in a time unit; and substantially increases accuracy and real time property of acquisition of a rotating speed signal.

Description

Etc. the precision frequency measurement circuit

Technical field

The utility model relates to a kind of frequency measurement circuit, relates in particular to precision frequency measurement circuits such as a kind of.

Background technology

Field control system, data acquisition and communication system, equipment monitoring system and man-machine interface unit have obtained using widely in industry-by-industry.

In Control System of Rotational Speed of Steam Turbine, accuracy and real-time that turbine speed is gathered require very high.Acquisition method commonly used is treated the measured frequency signal and is counted for utilizing single-chip microcomputer in unit interval inside counting method in the unit interval.Detected pulse signal number error is 1 in unit interval, and the measuring accuracy of this method can produce than great fluctuation process because of the height variation of frequency.

The error of pulse signal number in the unit interval inside counting method improves accuracy and real-time that rotating speed is gathered, the precision frequency measurement circuit such as is necessary to provide.

The utility model content

The utility model technical matters to be solved provides precision frequency measurement circuits such as a kind of, and the error of the pulse signal number that elimination unit interval inside counting method is brought improves accuracy and real-time that tach signal is gathered.

The utility model is to solve the problems of the technologies described above the technical scheme that adopts to provide precision frequency measurement circuits such as a kind of; Comprise first counter, second counter and frequency counter; Wherein, Measured signal links to each other with the input end of clock of first d type flip flop, second d type flip flop respectively, and the output terminal of said first d type flip flop links to each other with the input end of first counter, and the output terminal of said second d type flip flop links to each other with the input end of second counter; The trigger end of said first d type flip flop links to each other with control signal START; Output terminal links to each other with the Enable Pin of first counter; The trigger end of said second d type flip flop links to each other with control signal STOP; Output terminal links to each other with the Enable Pin of second counter, realizes control signal and measured signal rising edge synchro control; The output signal of said frequency counter links to each other with the input end of clock of first counter with the back with the output signal inversion of second d type flip flop; The output signal inversion of the said measured signal and second d type flip flop links to each other with the input end of clock of second counter with the back.

Precision frequency measurement circuit such as above-mentioned; Wherein, Said measured signal links to each other with the input end of first d type flip flop, second d type flip flop respectively after the shaping pre-service through first phase inverter, second phase inverter realization signal through the signal after the opto-electronic conversion through the optocoupler input circuit again.

The utility model contrast prior art has following beneficial effect: the utility model provide etc. the precision frequency measurement circuit; Through two d type flip flops are set two counters are counted synchronously; Eliminate the error of the pulse signal number that unit interval inside counting method brings, significantly improved accuracy and real-time that tach signal is gathered.

Description of drawings

Fig. 1 be the utility model etc. precision frequency measurement circuit synoptic diagram;

Fig. 2 is the precision regulating circuit synoptic diagram of the utility model;

Fig. 3 is the input shaper circuit diagram of the utility model;

Fig. 4 be the utility model etc. precision measured frequency method synoptic diagram;

Fig. 5 be the utility model etc. precision measured frequency method flow diagram;

Fig. 6 is etc. that precision frequency measurement circuit and method are used synoptic diagram in the turbine speed test macro.

Among the figure: 1 first d type flip flop; 2 second d type flip flops; 3 frequency counters; 4 first counters; 5 second counters; 6 comparers; 7 first phase inverters; 8 second phase inverters; 9 optocoupler input circuits.

Embodiment

Below in conjunction with accompanying drawing and embodiment the utility model is done further to describe.

Fig. 1 be the utility model etc. precision frequency measurement circuit synoptic diagram.

See also Fig. 1; The utility model etc. the precision frequency measurement circuit comprise first counter 4, second counter 5 and frequency counter 3; Wherein, Measured signal links to each other with the input end of clock of first d type flip flop 1, second d type flip flop 2 respectively, and the output terminal of said first d type flip flop 1 links to each other with the input end of first counter 4, and the output terminal of said second d type flip flop 2 links to each other with the input end of second counter 5;

The trigger end of said first d type flip flop 1 links to each other with control signal START; Output terminal links to each other with the Enable Pin of first counter 4; The trigger end of said second d type flip flop 2 links to each other with control signal STOP; Output terminal links to each other with the Enable Pin of second counter 5, realizes control signal and measured signal rising edge synchro control;

The output signal inversion of the output signal of said frequency counter 3 and second d type flip flop 2 links to each other with the input end of clock of first counter 4 with the back; The output signal inversion of the said measured signal and second d type flip flop 2 links to each other with the input end of clock of second counter 5 with the back.

In order further to realize the adjustable of measuring accuracy; Measured signal can be handled through the precision regulating circuit; Thereby the precision regulating circuit can be realized the adjustable, as shown in Figure 2 of measuring accuracy through the threshold voltage of selecting different divider resistances to change input circuit.Four divider resistances (RS1, RS2, RS3, RS4) are when all disconnecting, and supply voltage 5V is added on R1 (39K ohm) and the R2 (1K ohm), R1 divide threshold voltage do

5V÷(39KΩ+1KΩ)*1KΩ＝125mV

The signal process comparer output that is higher than at this moment 125mV is 1 all, and the signal process comparer output that is lower than 125mV all is 0, and in order to guarantee measuring stability, the threshold voltage that the qualification user imports is 250mV, and measuring accuracy is the highest; When connecting divider resistance RS1 (20K ohm), the resistance value after RS1 and the R1 parallel connection is 13.2K ohm, and this moment, threshold voltage did

5V÷(13.2KΩ+1KΩ)*1KΩ＝350mV

Output is 1 all to the signal that be higher than 350mV this moment through comparer, and output all is 0 through comparer to be lower than the signal of 350mV, and in order to guarantee measuring stability, the threshold voltage that limits user's input is 500mV, and measuring accuracy is time high.By that analogy, the different divider resistance value of gating promptly can realize the adjustable of measuring accuracy.

Measured signal can carry out pre-service through shaping circuit: measured signal is realized the isolation of input circuit and metering circuit through the optocoupler input; Guaranteed the anti-interference of measuring;, as shown in Figure 3 through the signal after the opto-electronic conversion again through the shaping pre-service of first phase inverter 7 and second phase inverter, 8 realization signals.

Fig. 4 be the utility model etc. precision measured frequency method synoptic diagram; Fig. 5 be the utility model etc. precision measured frequency method flow diagram.

See also Fig. 4 and Fig. 5, the utility model etc. precision measured frequency method following:

1) first counter 4 (16 digit counter) and second counter 5 (8 digit counter), high level allows counting.Standard-frequency signal adopts the signal of 2.5MHZ: with the signal of 20MHZ from the input end of clock C input of frequency counter 3 (4 digit counter) through transferring the frequency signal of 2.5MHZ behind eight frequency divisions to; This frequency signal is from the input end of clock C input of first counter 4, and defining its frequency is Fs; From the input end of clock C input of second counter 5, survey frequency is Fx after the external circuit shaping in measured signal.

2) rising edge of first d

type flip flop

1 and 2 couples of measured signal Fx of second d type flip flop detects, and realizes that control signal (START/STOP) and Fx rising edge are synchronous.

When START was high level, the rising edge of measured signal started first counter 4 and second counter 5 simultaneously through the trigger end Q of first d type flip flop 1, and measured signal Fx and standard-frequency signal Fs are counted simultaneously.When STOP is high level; The rising edge of measured signal is through the trigger end Q output high level signal of second d type flip flop 5; After this high level signal negate with frequency signal with; Make the input end C level of the win counter 4 and second counter 5 remain low level, realize stopping simultaneously the counting of first counter and second counter.

So just guaranteed that 5 pairs of measured signal countings of second counter just are an integer cycle, and the error of 1 pair of reference signal counting of counter is positive and negative 1 pulse.

3) being located in gate time T the measured signal count value is Nx, is Ns to the count value of standard-frequency signal, and then the frequency values of measured signal is: Fx=(Fs/Ns) * Nx, and as shown in Figure 4.

4) behind the completion one-shot measurement, control chip sends the CLR signal, simultaneously zero clearing first counter 4 and second counter.

5) measured signal converts the high-low level signal to through comparer; In order to guarantee that signal input circuit can the interferometry circuit; Between input circuit and metering circuit, connect realization photoelectricity and isolate, carry out shaping through first phase inverter 7 and second phase inverter 8 again through the signal after the opto-electronic conversion and handle through optocoupler.

6) threshold voltage of adjusting comparer 6 can be realized the adjusting of the measuring accuracy of measured signal.Send instruction through single-chip microcomputer, divider resistance that gating is different and then adjusting threshold voltage are realized the adjusting of measuring accuracy.

Please continue referring to Fig. 6, the utility model provide etc. the precision frequency measurement circuit, can be the programmable logic controller (PLC) spare of XC9572XL through selecting model for use; The single-chip microcomputer of STC12C5A; The comparer of LM393, the photoelectricity coupling converter of 4N35, the phase inverter of 74HC14 makes up., also can pass through programmable logic controller (PLC) spare (CPLD) and make up.The performance of facing the system that adopts precision frequency measurement methods such as CPLD counting is down tested, and does contrast with original unit count method.Two systems all adopt STC12C5A chip, XC9572XL chip and identical shaping circuit, through identical signal is gathered, are transferred to upper computer software output through data communication and show in the experimental system.Detect rotational speed pulse signal and forward 11000 acquisition precision and the acquisition times that change to from 1.

Can know from last table; Adopt the utility model etc. the precision frequency measurement circuit all obtained significant raising in the precision and the performance aspect the speed of gathering rotating speed; Eliminate the error of the pulse signal number that unit interval inside counting method brings, significantly improved accuracy and real-time that tach signal is gathered.

Though the utility model discloses as above with preferred embodiment; Right its is not in order to limit the utility model; Any those skilled in the art; In spirit that does not break away from the utility model and scope, when can doing a little modification and perfect, so the protection domain of the utility model is when being as the criterion with what claims defined.

Claims

1. precision frequency measurement circuit such as a kind; Comprise first counter (4), second counter (5) and frequency counter (3); It is characterized in that; Measured signal links to each other with the input end of clock of first d type flip flop (1), second d type flip flop (2) respectively, and the output terminal of said first d type flip flop (1) links to each other with the input end of first counter (4), and the output terminal of said second d type flip flop (2) links to each other with the input end of second counter (5);

The trigger end of said first d type flip flop (1) links to each other with control signal START; Output terminal links to each other with the Enable Pin of first counter (4); The trigger end of said second d type flip flop (2) links to each other with control signal STOP; Output terminal links to each other with the Enable Pin of second counter (5), realizes control signal and measured signal rising edge synchro control;

The output signal inversion of the output signal of said frequency counter (3) and second d type flip flop (2) links to each other with the input end of clock of first counter (4) with the back; The output signal inversion of said measured signal and second d type flip flop (2) links to each other with the input end of clock of second counter (5) with the back.

2. precision frequency measurement circuit such as as claimed in claim 1; It is characterized in that; Said measured signal links to each other with the input end of first d type flip flop (1), second d type flip flop (2) respectively after the shaping pre-service through first phase inverter (7), second phase inverter (8) realization signal through the signal after the opto-electronic conversion through optocoupler input circuit (9) again.