DE2353473A1 - Pulse train frequency fluctuations measuring device - uses frequency-to-voltage converter and electronic quotient forming network - Google Patents

Abstract

The network forms the ratio of the fluctuation amplitude to the mean frequency. It consists of an amplifier with a logarithmic characteristic, to whose input the long term mean value of the d.c. voltage and the fluctuation components are applied. A high-pass filter whose time constant can be varied, is connected to the amplifier output. The quotient forming network is connected through a voltage controlled blocking element to the high-pass filter, whose time constant is automatically reduced when the long term mean frequency value at the network output changes, while the fluctuation a.c. component is prevented from reaching the filter by the blocking element. It is an RC low-pass filter, whose time constant can be switched by a field-effect transistor.

Description

AG FA-GEVAERT

PATENT DEPARTMENT

LEVERKUSEN

Ki / de

2 4th OHt. 1973

Device for measuring relative frequency fluctuations

The invention relates to a device for measurement and registration of relative frequency fluctuations of a pulse train. In particular the invention is suitable for monitoring the speed fluctuation of rotating shafts or the speed fluctuation of evenly moving paper or film webs. With devices of this type, one with the speed resp. Speed proportional frequency using a frequency voltage converter converted into a speed-analog voltage and related to the mean value of the frequency by means of an electronic quotient network.

Pulse sequences can, for example, be! By means of electronic Generate generators, but also by mechanical pulse generators on an optical, inductive or mechanical basis.

In many cases the working speed of a production machine directly determines the quality or the physical one or chemical properties of the product. For example, a mechanical pulse encoder with a negligibly small pitch error is coupled to a rotating shaft of a such a machine, it can be seen from the fluctuation of the frequency the pulse train directly on the fluctuation in speed or Close peripheral speed of this wave. Conversely, the pulse train fluctuation provides one with constant angular velocity driven pulse encoder whose division error. Other application examples are the measurement of pitch fluctuations on tape recorders, the frequency jitter in pulse generators.

A-G 1164:

509818/0623

Many based on pulse train fluctuation measurements Measurement methods require knowledge of the relative frequency fluctuation based on the time average of the Pulse train.

Such a measuring device is for example in the German patent specification DT-PS 1 056 403 described. With the help of a quotient network, this device forms the quotient from the Fluctuation amplitude and the mean value of the pulse train over time. The accuracy and the scope of the measuring range are determined by the built-in magnetic switch and the quotient stage are severely limited. With sequential operation of the measuring device with The device has too long a response time for several measuring points.

The main object of the invention is therefore to improve this measuring device is based. In particular, the operational safety, the measurement accuracy, the measurement scope and the Calibration stability can be increased.

This object is achieved in the device described above according to the invention in the following way: The quotient network consists of an amplifier with a logarithmic characteristic, whose input is _{supplied with the long-term mean value of the direct voltage U m} and the fluctuation amplitude U and whose output is followed by a switchable high-pass filter.

A further development of the invention provides _1, that the output of ratio network is connected via a voltage-controlled locking member T ₂ with the high-pass filter R ₁ C _1, and the time constant of the high pass filter is automatically reduced when the long-time mean value U at the output of ratio network changes, while the output _{alternating voltage U as} (T) of the quotient network is automatically separated from the input of the high-pass filter _{by the blocking element T 2.} An R / C element can be used as a blocking element and a C / R element can be used as a high-pass filter. In both cases the resistors are bridged with field effect transistors so that the time constants can be switched.

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Further improvements of the device, for example the installation a display lock and a limit value display are described in more detail in the claims.

With the new device, a significantly higher temperature stability becomes a greater one. Frequency range, a lower offset and better linearity. Another advantage lies in the extended; Measuring range with improved accuracy at the same time. A measurement accuracy of approx. + 1 % is achieved. Since a logarithmic function can be represented precisely even over long periods of time, there is no need to recalibrate the measuring device. · ■ "■" .- ■ ^;

With the switchable high-pass filter you can achieve a shorter one Reloading time of the high-pass filter and thus a reduction in the response time to ^. 5 s.

In the following, an embodiment of the invention is based on described in more detail by drawings. Thereby also the principle the circuit explained in more detail .; Show it:

Figure T :. .A block diagram of the measuring arrangement Figure 2: The principle of the F / U conversion Figure 3: The mode of operation of the quotient network and Figure 4: The switchable high-low-pass filter with ■. Display lock and speed value display.

The measurement object, e.g. a rotating shaft 1, is provided with a photoelectric encoder 2 mechanically coupled directly. the The time function of the speed n (t) can be divided into two components:

^{n (t)} = ⁿ

decompose, a constant component η (mean speed) and "a fluctuation component η (t) _.: - -

The time function of the pulse frequency f (t) of the encoder 2 is .proportional to the time function n (t) of wave 1:

".. f (tW n (t). (2)

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This frequency-time function is generated by the frequency-voltage converter 3 (F / U conversion) converted into a proportional voltage-time function U (t):

UCtW f (t) (3).

Because between the output voltage of the F / U converter and the speed according to Relationship (2) proportionality results:

n (t) (4)

and taking into account equation (1):

U (t) = U _m + U _s (t) (5)

The following quotient stage 4 forms the quotient from the fluctuation function U _g (t) and the mean voltage U _m :

• This quotient is given by the relationship (4) and the equation (1) proportional to the speed fluctuation based on the average speed;

U _s (t) n _s (t)

that is, the desired measurand.

The alternating voltage occurring at the output of the quotient network 4 is then a switchable high-low-pass filter 5 and displayed after amplification in the amplifier 6 by the display instrument or the recorder 7. The individual function groups 2 to 6 are described in more detail below.

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■■, ■. ■■ "■" ■■ Γ - - - ■ -.-.

1st encoder,;

The encoder 2 has the task of a rotary movement or a Another process depicted as a rotary movement, one of the angles to generate a proportional number of electrical impulses.

It is designed, for example, as a photoelectric transmitter and consists of a rotatably mounted impulse disc, which is divided into slits or bar marks arranged in the shape of a spoke high pitch accuracy is provided. The pulse disc periodically interrupts a light beam with its graduation marks, which is directed from a fixed light source onto a fixed photodiode. The photodiode converts converts the light pulses into voltage pulses.

2. F / tr converter,

In the F / U converter 3 (Figure 2), the voltage pulses of the Encoder 2 is converted into voltage pulses of constant pulse height U and constant pulse duration by a monostable multivibrator. If the following active low-pass filter suppresses all frequency components above a limit frequency, see above the following is obtained as the output voltage Ü_ of the low-pass filter:

thus one proportional to the speed or speed Tension. -

3. Quotient network

In the quotient network (FIG. 3), a non-linear characteristic curve with the output voltage of the is obtained by modulating F / U converter 3 according to equation (8) according to the quotient Equation (6). The logarithmic function serves as the non-linear characteristic:

uv = K.mu _e (9)

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At the operating point A of the characteristic, which is set by the voltage U, the output alternating voltage U _as (t) results as:

u _as (t) = v (u _m ). . ü _a (t) (10)

The gain V (U) of the quotient level is equal to the slope of the characteristic curve at operating point A (tr = U):

With equation (9) now becomes

d (k. In U _e )

this gives equation (10):

(t)

u _as (t) = k.

^U m

i.e. the required quotient according to equation (7)

4. Switchable filter with amplifier (FIG. 4) The alternating output voltage U (t) of the quotient network 4

do ..

is decoupled by a high-pass filter R ^ C ^, amplified in V ^, in a further amplifier V ₉ to a proportional to U __ (t)

i - CLO

Converted electricity and fed to a recorder calibrated in%. For the detection of very low-frequency modulated pulse train fluctuations (A ^ speed fluctuations) here 0.01 Hz - R ^, (L = 16 s is dimensioned; however, this means, for example, when the device is operated sequentially with several encoders with different average speeds, one of R ₁ C, dependent, unreasonably long transient response of the device.

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This is why the time constant R ₁ C ₁ is reduced with T ₁ so that C ₁ can adjust to U_ in a few seconds. At the same time, U (t) is passed through a low-pass filter that can be switched on _{with T 9}

as. £ L.

R ₂ Cp separated from the input of the high pass filter. ;

The operation of the device under frequently changing operating parameters (continuous or spontaneous changes in the long-term mean value U, exceeding the measuring range

by U _ (t)) required to avoid overloads as

of the recording device as well as later inexplicable diagram recordings a control of the device by a display lock. As long as the pulse generator does not deliver a pulse train, the display of the device is locked by the flip-flop FF, i.e. T ₁ conductive and T ₂ locked (the source of T ₁ is virtually on 0).

One of 0 to increasing pulse repetition frequency cancels the retriggerable mono-flip-flop-side lock of the unit MF via the OR-gate R, when a set "pulse train frequency is exceeded * At the same time via the impedance converter I to capacitor C ₁ to U is loaded and holds that

ι dm -..---

Device with the flip-flop FF via the charging current detector Z- .. - D with the logic output Ι _β1 0 blocked via R until no more charging current flows via C. If C _{1 is} loaded, the logic signal appears. I _c1 = 0. The logic signal I ₂ = 0 appears when U __ (t) goes through 0. Both signals are processed in the AND gate U

el S -

ties and releases the flip-flop FF. This means that T _{1 is} blocked and T _{2 is switched} on after a delay Z.

A limit value detector GW 1 generates a logic at its output

signal, if-U „ _a (t) is the measuring range limit of the device, there- fore. as

represents by a Schwellspänhung U ^ ₁ exceeds. One

Blocked again, the device can now only be upgraded using the. Limit value detector GW 1 initiated - and possibly via the logic signal. I _Λ ^ O can be maintained in the sense described above. ^{If U __ (. T) exceeds} a second (digitally adjustable) threshold voltage O ^ 2 ^ ¹¹ GW 1 ' ^{s0 (äiXl} gt the limit value detector GW 2 at its output a logic signal that has

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a retriggerable mono flip-flop switches on the fast feed of a recorder. If the relative pulse train fluctuations or speed fluctuations with U (t) exceed the threshold voltage IL ^ ₂ P ^r0 time unit several times, an alarm signal is triggered.

5. Control and calibration generator

Since an operational functional test and calibration of the device is not possible with artificially generated defined pulse train fluctuations on the encoder, this function takes over built-in digital - frequency-modulated pulse generator of the can optionally be connected to the input of the F / U converter - even during the actual measurements. Generated here a quartz generator via a frequency divider with a finely graded digitally selectable division factor a pulse repetition frequency. By continuously digitally changing the division factor in very small binary steps in a time-constant sequence between Two digitally defined limits result in a quasi-linear triangular frequency modulation of the pulse repetition frequency absolutely defined frequency deviation. The stroke frequency is expediently chosen so that it is well below the cutoff frequency of the scribe lies.

6. Technical data for an exemplary embodiment

The one with the described device for measurement and registration Outstanding data from relative pulse train fluctuations for a measuring range U (t) = + 10 96 are:

~ u _s (t)

a) The formation of the quotient | j over a range of

1 U _m to U ^ 40 _m. ^m

b) Measuring range of the fluctuation frequency 0.01 Hz to 100 Hz (-3dB) for f (t) ^ -300 Hz (for the definition of f (t) see Eq. 2).

c) Measurement accuracy over the quotient measurement range <£ + 1 % for f (t) ^ 1300 Hz

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509818/0623

Claims (9)

Claims M ^ N device for measuring and registering relative frequency fluctuations in a pulse train, using a frequency-voltage converter and an electronic quotient network in which the fluctuation amplitude U_ and the mean value U of the pulse train are related to each other, characterized in that the quotient network "(4) consists of an amplifier with a logarithmic characteristic, whose input is _{supplied with the long-term mean value of the direct voltage U m} and the fluctuation component U_ and whose output is followed by a high-pass filter (5) that can be switched with respect to its time constant. 2. Device, in particular according to claim 1, characterized in that the output of the quotient network (4) is connected to the high-pass filter (5) via a voltage-controlled blocking element and the time constant of the high-pass filter is automatically reduced when the long-term average value U _n at the output The quotient network (4) changes, while the output AC voltage U _ (t) of the quotient network (4) is automatically separated from the input of the high-pass filter (5) by the blocking element. 3. Apparatus according to claim 1-2, characterized in that the Blocking element is an RC low-pass filter (RpjCp), the time constant of which by means of of a field effect transistor Tp is switchable. 4. Apparatus according to claim 1-3, characterized in that the high-pass filter is a CR element (C ₁ R ₁ ), the time constant of which can be switched to lower values _{by means of the field effect transistor T 1.} .. " 5. Apparatus according to claim 1-4, characterized in that the display of the device is _{blocked for the duration of the charge reversal of the capacitors C 1} and Cp. , A-G 1164 - 9— 509018/0623 6. Apparatus according to claim 1-5, characterized in that the low-pass filter is switched by means of the field effect transistor T ₂ later than the high-pass filter with the field effect transistor T ^ "' 7 «Device according to claims 1-6, characterized in that a display lock is provided - which comes into operation when the fluctuation _{amplitude U g} (t) exceeds the limit value U ^ ^ of the measuring range. 8. Apparatus according to claim 1-7, characterized in that a further limit value switching device is provided which only releases the measured value registration for a defined time when the fluctuation amplitude U_ (t) exceeds a digitally adjustable limit value U _n ^ r _o. 9. Apparatus according to claim 1-7, characterized in that a digital frequency-modulated calibration generator (8) is also installed for control and calibration. A-G 1164 - 10 - 509818/0 623 Blank page