DE1068374B - Procedure for frequency measurement with undelayed display - Google Patents

Description

The invention relates to a method for frequency measurement with instantaneous display in which the voltage of the frequency to be measured in an equal frequency pulse sequence with alternating positive ones and negative pulses is converted and the amplitude of a sawtooth wave synchronized with the positive pulses of the period duration of the vibration to be measured is proportional.

Methods for frequency measurement are known in which the input oscillation is limited by limiting the amplitude obtained a square wave and with the resulting square pulses a capacitor is charged. The charging current of this capacitor is then proportional to the frequency.

Furthermore, methods are known in which, as a measure of the frequency to be measured, that of. the frequency the input voltage-dependent amplitude of a sawtooth oscillation is used. The Input voltage in suitable amplifier, dif- ao renzier- and limiter stages initially formed voltage peaks, i.e. pulses, of the same amplitude. With one of the known arrangements, these impulses are then transmitted to the control grid of a thyratron tube given the breakover oscillations in a known manner via a capacitor and a resistor generated. These tilting vibrations are then made visible via a cathode ray oscillograph and appear on its luminescent screen as straight lines of a certain length. In doing so, these lines are the shorter the higher the frequency of the applied voltage. In another known arrangement the voltage peaks of constant amplitude obtained from the input voltage are transferred a rectifier of a capacitor resistor parallel circuit, whose time constant is approximately below the lowest frequency to be measured, supplied, where the resistance of the parallel connection to the internal resistance of the source for the Voltage peaks is chosen so large that the breakover voltage that arises at the parallel circuit, which serves as the deflection voltage for the cathode ray oscilloscope, one of the frequency of the voltage spikes has dependent amplitude.

With these arrangements, which continuously display a frequency spectrum, the exact detection of a certain, fixed frequency very difficult, or it occurs when displaying certain frequencies as a result of the rectification required here and the associated increase in the time constants unwanted delays in the orders.

In contrast, the method according to the invention enables precisely the point in time of the passage of the changing frequency to be measured through a method for frequency measurement
with immediate display

Applicant:

Telefunken GmbH,
Berlin NW 87, Siddngenstr. 71

Dr.-Ing. Alois Egger, Constance (Lake Constance),
has been named as the inventor

to detect a fixed, specified frequency value and then to trigger a switching pulse without delay.

The method according to the invention achieves a sawtooth oscillation synchronized with the input frequency an exact and undelayed display of the instantaneous frequency by the period duration by determining one of the inclined saw tooth flank in a certain fraction of the period reached height is measured.

The method according to the invention will now be explained with reference to FIGS. 1 and 2. The drawings show the the following waveforms, d. H. the instantaneous values of the voltages as a function from the time. Fig. 1 shows the case of purely sinusoidal oscillations for three different input frequencies, on the left is too high, in the middle the frequency whose occurrence is to be displayed, and on the right too small a frequency. Fig. 2 explains the case of non-sinusoidal oscillations, but according to the assumption have no more than two zero crossings in each period.

The letters in parentheses that appear in the following explanations refer to the identically labeled lines in FIGS. 1 and 2.

The periodic, generally non-sinusoidal input voltage to be measured with only two zero crossings per period (α) or (i) is first converted into a square-wave voltage (V) or (F) in a known manner by amplification and double-sided limitation and then through Differentiate into a sequence of positive and negative impulses (c) or (!). Furthermore, as already proposed, the sawtooth voltage (e) or (»), which starts from zero, is then synchronized with the positive pulses, (d) or (w). The resulting amplitude level of the sawtooth voltage, which is dependent on the input frequency, is compared according to the invention with an adjustable DC voltage () (see line e) via an amplitude-selective network, which

'909 647/192

Claims (7)

works in such a way that when the same * voltage values are reached, a pulse is emitted. This gives a pulse sequence (J) from (d) and (e). Every second pulse (J) is, in general, not exactly in the middle between the two! Positive pulses, which β indicate the beginning or the end of the period. By doing. Special case of purely sinusoidal oscillations denote the above unused negative pulses of line (c) the middle of the period. If you combine these pulses (see line g) with the pulses (J) in such a way that a switching process is triggered when two of them coincide, this only occurs when the frequency to be measured is the same as the predetermined frequency. If the frequency is periodic but not sinusoidal, as shown in FIG. 2, the method can also be used, only then, instead of the pulses (g), which are supposed to lie in the middle between two successive sawtooth edges, other pulses must be generated. In a further development of the invention, the easiest way to do this is to rotate the synchronized sawtooth voltage («) by 180 ° (cf. c) and obtain a pulse sequence (p) by comparing the amplitude of the voltage curves («) and (0). With the help of the positive pulses (m), the pulses that appear at the times of the steep sawtooth flank can be suppressed, so that pulses (q) are obtained exactly in the middle between the sawtooth flanks. The further evaluation takes place as described above. The case of non-sinusoidal oscillations can either be detected by determining the center of the period in the manner shown, or the method similar to sinusoidal oscillations can be used if the ratio of the two half-waves is constant and known, so that every second zero crossing the period in shares a known relationship. The DC voltage μ is then chosen so that it corresponds to the period of the frequency to be detected at this partial point. Claims; 1. Procedure for frequency measurement with instantaneous display, in which the voltage of the to measure the frequency in a pulse train of the same frequency is converted with alternating positive and negative pulses and the amplitude a sawtooth wave synchronized with the positive pulses of the period duration of the to measuring oscillation is proportional, characterized in that the period duration is determined by one of the inclined saw tooth flank in a certain fraction of the period reached height is measured. 2. The method according to claim 1, characterized in that the height of the tooth, for example in the middle of the inclined sawtooth flank, is compared with a DC voltage, which in this circuit corresponds to a certain frequency. 3. The method according to claim 2, characterized in that when the same Spamtday values are reached a pulse (/) is emitted from the sawtooth and reference voltage. 4. The method according to claim 1, characterized in that that the period is derived from the input oscillation to be measured negative momentum (g ") is divided into a certain ratio. 5. The method according to claim 3 and 4, characterized in that when the pulses (/) and (g) coincide, a display or switching device is triggered. 6. The method according to claim 2, 4 and 5, characterized in that pulses are derived exactly in the middle between the steep sawtooth flanks from the sawtooth voltage itself by turning this («) with a sawtooth voltage (0 ) so kotnbi: niert that pulses (p) are triggered at the intersection of the rising and falling edges. 7. The method according to claim 6, characterized in that every second pulse (p) is canceled by a counter pulse (w). Considered publications:
German patent specification No. 692 696. 1 sheet of drawings ι 909 € 47/192 10.59