外文翻譯--高精度頻率計(jì)（英文）

1、PRECISION FREQUENCY METER B. A. Furman and I, I. Verzin UDC 621.31%76 Frequency is becoming an increasingly widespread parameter used for control, conversion, and measurement purposes at the present development stage

2、 of automatics, measurements, and the display and conversion techniques, Digital methods for measuring and converting frequency are the most precise. There exist methods for improving considerably the precision class of

3、analog frequency converters and frequency meters. The circuit of a high-fre- quency to adc signal converter is described in this article. The converter is used as a frequency meter with an out- put to a class 0.1 pointer

4、 instrument. The basic principle of analog instruments, used in designing this frequency meter, consisted of detecting the mean value of the voltage by integrating the measured frequency pulses which were calibrated with

5、 respect to their duration and amplitude. The error of such devices depends virtually on their calibration stability with a varying sup- ply voltage and temperature. A high precision was attained in this circuit by shapi

6、ng the duration of the integrated pulses by means of a crystal-stabilized generator in combination with a high-precision voltage stabilizer. The application of this method [1] made it possible to reduce the basic error o

7、f the frequency meter to 0.01%. However, the additional errors of actual circuits prevent the attainment of this precision. Below we analyze the pos- sibilities of applying such circuits for designing a frequency meter.

8、The frequency meter (Figs. i and 2) consists of a pulse-duration shaping circuit, a pulse-amplitude shaping cir- cuit, and an integrating unit. The duration shaping circuit consists of a synchronizing gate controlled by

9、clock fre- quency generator CG. In the absence of an input signal trigger 1Tr is in position 1, gate AND is blocked and trigger 2Tr is in position O. The duration shaping circuit (trigger 2Tr) has a low output potential.

10、 On receiving a pulse of the measured fre- quency, trigger 1Tr is tripped, the AND gate becomes conducting, and the routine clock pulse sets trigger 2Tr to po- sition 1. The following clock pulse returns trigger 2Tr and

11、then trigger 1Tr into their initial positions. Thus, every received pulse of the measured frequency produces a potential difference at the output of trigger 2Tr. This differ- ence lasts one period of the dock frequency.

12、The stability of the duration shaping circuit is determined by that of the clock frequency generator and the edges of the voltage drop pulse at the output of trigger 2Tr. A crystal-stabilized generator maintains its freq

13、uency over a wide temperature range without thermostatic con- trol with a precision of 10-s. The basic instability in shaping the pulse duration thus depends on the switching time of the cimUit transistors. The switching

14、 time of a saturated transistor consists of the duration of the effective pulse edges and the time required to switch from the saturated state. It should be noted that, since the output transistor 2Tr and the input trans

15、istor of switch S operate in phase opposition, a partial or complete compensation of the effect of their lagging and the output pulse duration can be obtained. In practice it is difficult to attain complete com- pensatio

16、n, especially over a wide temperature range. /t input AND Fig. 1. Block schematic of the frequency meter. r , - , - 2g V From the out- ~ fa 1, ~ ~, (stab,) putof2Tr , Y 2^ “ ~r2 ~“ Fig, 2. Output pulse shaping

17、circuit. Translated from Izmeritel'naya Tekhnika, No. 4, pp. 31-33, April, 1968. Original article submitted July 14, 1967. 470 A further raising of the saturation ratio has a beneficial effect on the operation of the

18、 amplitude shaping cir- cuit, but it impairs the stability of the duration shaping circuit. The above pulse duration determines the frequency measuring limit. Thus, fmax <2500 Hz for tp = 200 #sec (taking into conside

19、ration the possibility of the measurements being delayed by one period according to the operating conditions of the synchronizing element). The above temperature error can be reduced, by means of a previously described p

20、arametric compensation, by a factor of 5-7 to a value not exceeding 0.0012%/~ in the temperature range of 20-50~ The total maximum er- ror of the pulse duration and amplitude shaping circuits in the above temperature r

21、ange will then remain below 0.07% (and rise to 0.1~ for a range extended up to +60~ The measured frequency range can be raised to 10 kHz for the same precision by using high-frequency transistors MP401-MP403. The exte

22、nsion of the frequency range is produced mainly by reducing the desaturation time. The limitation of the temperature range by +50~ in this case is due to a sharply rising effect of the uncontrolled collector current of

23、germanium transistors on the total error of the transducer, Our industry has developed recently the production of new types of silicon stabilitrons with a high thermal sta- bility of their stabilized voltage. The tempera

24、ture coefficient of voltage for stabilitrons D818D-D818E amounts re- spectively to 0.002 and 0.001%/~ for a nominal dynamic resistance of 18 f~. Their application leads toa simplifi- cation of the frequency meter circui

25、t without impairing its high stability or wide frequency range, In the improved version of the circuit the special stabilizer of the voltage compensation type is replaced by a simple two section parametric stabilizer wit

26、h stabilitrons D1-D2 (D816D-D818E) in the collector circuit of the shap- ing-switch transistor T I (Fig. 4). In this circuit the output resistance of the switch is determined in its open condi- tion by the resistance of

27、 saturated transistor TI, and in its closed condition by the dynamic resistance of the stabili- iron over its stabilizing range, Thus, the instability of the voltage level at the output of the closed switch is now deter-

28、 mined by the temperature coefficient of voltage of stabilitron D z instead of current variations with heat, This makes it also possible to use high-frequency transistors MP401-MP403 over a wide temperature range up to

29、+ 60~ The collector voltage of a saturated transistor type MP401-MP403 is lower than that of MP20-MP106. This can be used for improving the voltage compensation by means of transistor Tz (of the same type) in order to o

30、btain a zero voltage at the frequency meter output. The above circuits were tested out with a digital frequency meter 4~3-4 and potentiometer PPTV1, The out- put pointer instrument consisted of class 0.1 millivoltmeter t

31、ype GOERZ-134420 (with a range up to 60 mV and a re- sistance of 10 t~). The precision class of the frequency meter is then determined virtually by that of the output instru- ment. Its total additional error did not exce

32、ed 0,107o for temperature variations in the range of 20-60~ and supply voltage changes of i 10%. The initial drift amounted to 0,3% in 3-5 rain after switching in the supply voltage, The lower frequency measuring limit

33、of 20 Hz is determined by the frequency properties of the integrating unit. Should it be necessary to raise the time constant of the output instrument an additional inductance is connected in series with its moving coil.

34、 The use of capacitive filters at the output of the switch impairs the transducer's linearity since it becomes difficult to obtain strictly equal time constants for the charging and discharging circuits of the ca- pa

35、citance. The above circuits for converting frequency into a dc current can serve as a basis for designing mass-produced analog frequency meters with a precision class of 0.t-0.2. The production of such instruments wilt s