DD223808A1 - METHOD AND CIRCUIT ARRANGEMENT FOR THE DIGITAL EVALUATION OF FREQUENCY ANALOGUE SIGNALS BZW. FOR DIFFERENTIAL FREQUENCY MEASUREMENT - Google Patents

Abstract

The invention relates to a method and an arrangement for the digital evaluation of frequency-analogue signals or for difference frequency measurement and is suitable for measuring electrical and non-electrical quantities such as electrical voltage, fiber tile, foils, pressures, paths, etc., wherein the measured variables on capacitances, Induktivitaets-, Resistance change u. a. are to be converted into frequency or period changes. The aim and object of the invention is to realize the digital evaluation of the frequency-analog signals with low technical-oeconomic effort, simple circuit design and short measurement time. According to the invention, the output signals of two frequency-analogue transducers, after conversion into square waves, are fed to a D flip-flop such that the output signal produces a square wave having a frequency exactly equal to the difference frequency of the two supplied signals. Since the difference frequency is a measure for the measured variable, the difference frequency is converted into a digital signal via a period duration measurement, in which exactly one period is selected for a start signal, which can be further processed in a computer.

Description

Field of application of the invention

The invention relates YND an arrangement for digital evaluation frequency analog signals to a method and suitable stand for measuring electrical and non-electrical Great ζ B for measurement of electrical voltages, etc fiber tile film thickness, paths, prints, said Meßgroßen through corresponding transducer in equivalent frequency or Penodendaueranderungen Furthermore, it is thus possible to carry out digital differential frequency measurement directly

The invention is preferably used in the process measuring or Betriebsmeßtechnik because they can be easily coupled to digital computer

Characteristic of the known technical solutions

Frequency-analog measuring methods first convert the non-electrical or electrical measured variable into an intermediate variable (frequency, phase angle, period duration) which is evaluated by further conversion. The evaluation of the intermediate variable by further conversion is characteristic of the characteristics of the frequency-selective measuring method and the subject of this invention

The conversion of the intermediate size (frequency phase change) into an electrical voltage (FM demodulation) and subsequent further conversion by means of an analogue digital converter into a digital output signal for the purpose of computer feeding are also known. Direct digital methods of frequency and period duration measurement / Frequency-analog measuring devices often use two frequency-analogue measuring transducers (eg oscillators) with the same transducers, whereby either only one transducers with the actual measured variable or both transducers are acted upon in opposite directions with the measured variable. Then two such measuring arrangements are required For frequency or Penodendauermessung and forms for the elimination of the temperature and environmental influences, the difference of the digital output signals / 1 / In DD-WP 140082 is proposed instead of the difference of the digital output signals, the D To generate ifference frequency of the two measuring oscillators by means of a mixer and evaluate them after filtering by a low-pass filter with the help of a preselection payer

Since in frequency-analog measurement arrangements, the measurement corresponds to the change in frequency or Penodendauer arise due to the law of digital Zahlfrequenzmessung for direct digital frequency or Penodendauermessung required resolution (smallest measurable frequency or Penodendaueranderung) correspondingly long measurement times and thus very poor dynamic behavior Although the predominantly analog method (FM demodulation with subsequent AD conversion) has significantly better dynamic properties, but the effort in the analog part to the conversion into an electrical voltage is large and this also determines the accuracy of the measurement method in the method of difference frequency (DDWP 140082) the temperature and environmental influences are well compensated, the effort is less than with two separate measuring arrangements and difference of the digital output signals, however, due to the analog formation of the difference frequencies z by means of mixing stage, amplifier and low passport still considerable In any case, the large measuring time in the digital measurement of the difference frequency and due to the analog method large circuit complexity are disadvantageous

Object of the invention

The aim of the invention is to develop a measuring method and a measuring arrangement for evaluating frequency-analog signals which has a simple circuit structure and can be realized with little technical and economic effort

-2- 263 380 3

Explanation of the essence of the invention

The invention has the object to develop a method and an arrangement that allows digital signal processing directly from the output of the frequency-analog converter and compensates for fluctuations in the supply voltages

To solve this problem, the known principle of compensation of temperature and environmental influences by subtraction of two signals containing these influences used, but the difference in the output signals of two frequency-analog converter (z oscillators) is done directly with digital means Erfmdungsgemaß the task is characterized solved that the output signals zweter frequency-analog converter after conversion into square waves by Impulsformerstufen be supplied to a D-type flip-flop that a signal at the clock input and the other at the D input is the output of the D flip-flop is also a square wave whose Frequency but exactly the difference frequency of the two zugefuhrten square waves corresponds to select exactly one period of the difference frequency takes this one the Q output of the D flip-flop and this leads to the clock input of two other D-flip-flop to the Q output of the 2 D Flip flop is with the D input of the 3 D flip-flop and connected to the input of an AND gate At the other input of the AND gate is the negated Q output of the 3 D flip-flop on a start signal in the form of a 0-1 jump At the D input of the 2 D flip-flop, the output of the AND gate thus supplies a time signal of exactly one period of the difference frequency, which is supplied to the enable input of a forward-backward counter For the mode of operation of the difference frequency formation with the 1 D-flip-flop is decisive that the D-flip-flop is known to the lying at the D input information only for The timing of the switching edge (eg B 01 edge) of the clock in the Q output takes over, regardless of which signals were previously present and stores them until the next relevant clock edge

Here, the output signals of the frequency-analog converters converted into square-wave oscillations lie with f, at the D input and f ₂ at the clock input (whose frequencies differ by the difference frequency Δf = f, f ₂ ), so that 1_f_2_

consecutively, the potentials H and subsequently the same potentials L are taken from the signal at the D input to the output. The fact that the D-flip-flop changes the signal between the switching edges are without influence and stored in the output information is stored, the output signal is a square wave with the period T _M = - Since the difference frequency Af a measure of for The measuring is big, the will be

Differential frequency evaluated by Penodendauermessung. With a circuit consisting of two D-type flip-flop and an AND gate, the shift chain with two D-type flip-flops is used to pick out exactly one period (two half cycles) of the difference frequency and feed it to the enable input at the payer Payer pays during this period the periods of a constant frequency f ₀ and provides a numerical result ζ = T _M f = Ia.

Expediently, one chooses a basic difference frequency Af _G , which corresponds to the zero value of the measured variable

- to reach a short measuring time,

- be able to evaluate positive and negative values of the measured variable easier

- When using oscillators as a frequency-analogue transducer to avoid mutual entrainment

For the determination of the number result of the fundamental difference frequency (zero point) to switch the payer to Vorwartszahlen from zero and maintaining to T _M = 1 / Af _G a number result Z ₀ = f _o / f _G This value for the zero point is stored and serves the next measurement for the preset value, if not, the "zero point" is to be redetermined Then the actual measuring process, the payer is switched to Ruckwartsbetneb The value displayed by the payer corresponds exactly to the measured variable, whereby positive measures are recognized by the fact that the payer Return codes go through zero However, the coding is the same for positive and negative measured variables. The circuit arrangement and the method thus have the following advantages

Digital signal conditioning directly from the output of the frequency-analog converter,

- Simple circuit, so less cost

- small measuring time

- low sensitivity to fluctuations in the supply voltage

exemplary

The measured quantity χ (Material B material content of a yarn, deviation of the thickness of a plastic film from the normal) generates a frequency change Af ~ x via a transducer 1 (eg oscillator with capacitance influenced by the measuring variable) so that fi = fio ^T - ^ f , where f _{10 is} the frequency of the converter 1 at χ = 0

The converter 2 has the same structure as converter 1, but is only subject to the environmental influences and generates the frequency f ₂ = f ₂₀ By forming the difference frequency, the environmental influences are largely eliminated As a payer, a forward / backward payer 10 is used (Figure 1) The frequency offset fi ₀ - U ₀ represents the zero point of the measuring arrangement, ie

Zero point detection and payer preset

x = 0, payer as forward payer,

Number result Z ₀ = - f ₀

40 ~~ Ti о

After this preparation and payer presentation, the actual measurement χ = -x _m , payer as Rückuckzahlzahler

_f °

40 ~ ^T 2 0 - -ІT

results

Dzw at χ = + Xm, payer as backpayer

gives 7 ._ = r -T7 ^f ₀

fio - T; o ⁺ -ι '

om

-z- 263 380

The count result is Az _n , = z _o - z _om . With a positive measurand χ = + x _m , z _om > z becomes ₀ , the counter then runs through zero; From this one obtains the sign of the measurand. The indicated value Az ₁₁₁ corresponds to the magnitude of the measured variable, whereby the zero point migration was compensated by environmental influences of the difference formation.

Claims (5)

1 method for digital evaluation of frequency-analog signals, characterized in that the output signals of two frequency-analog converter (1,2) by pulse shaper (3,4) are converted into square waves, these are fed to a D-type flip-flop (5) such that the a signal at the D input and the other signal is at Taktemgang and thereby at the output, the difference frequency of the input signals occurs from the combination of a 2D flip-flop (6, 7) and an AND gate (8) to a specific Start signal half a or a multiple of half a Penode picked out and fed to a payer (10) for Penodendauermessung -1- 263 380 3 invention claims 2 method according to item 1, characterized in that for the determination of the number value of the basic difference frequency of the payer (10) is set from the zero point to forward numbers, this value is stored for the zero point and is used for the measurement process as Zahiervoreinstellung 3 Method according to items 1 and 2, characterized in that for the measuring operation the payer (10) is set to backward operation and the value indicated by the payer (10) corresponds to the measured variable, whereby negative measured values are recognized by the payer (10) when returning numbers the zero point happened 4 Method according to items 1 and 2, characterized in that a forward pay meter is used both for the determination of the basic difference frequency and for the determination of the value of the measured variable and the difference formation for determining the actual measured value takes place in a downstream computer 5 arrangement for carrying out the method according to item 1 to 4, characterized in that two parallel frequency-analog converters (1, 2) each have a pulse shaper (3, 4) is followed, the outputs of which with a D flip-flop (5) are coupled, that one is at the clock and the other at the D-Emgang and whose Q output is coupled to the clock input of two further D-type flip-flop (6,7) and that the Q output of the second D-flip Flop (6) to the D input of the third D flip-flop (7) and an AND gate (8) whose second input is coupled to the negated Q output of the third D flip-flop (7), is connected and that the output of the AND gate (8) is coupled to the enable input of the payer (10), preferably forward / Rückzahlzahlzahler, at the input of a constant frequency is applied by an additional oscillator (9) or a the two parallel frequency-analog converter (1 2) can be realized For this 1 page drawing