Verification plan of universal counter (frequency meter)

Based on the general purpose counter JJG349-2014 verification regulation, this paper briefly explains the functions and tests of the universal counter, analyzes its measuring method in its measuring standard system, perfected the recording function of the measuring data, and formed a set of interrelated data system analysis under the original test category, which is favorable for the market to optimize and test the universal counter conveniently.

Measuring frequency, cycle time interval, frequency ratio, cumulative count, timing and so on, together with the corresponding plug-in, can also measure phase, voltage and so on. Its basic working principle is to accumulate the oscillating frequency of the input signal in the predetermined standard time (gate time) with the appropriate logic circuit, or to measure the number of the standard time (Shi Ji) signal in the time interval to be measured, and to measure the frequency, period and time interval; the basic circuit is composed of input channel, Shi Ji generation and transformation unit, main gate, control unit, counting and display unit, etc. it has many measuring functions, mainly including frequency, cycle and time interval measurement, and usually includes frequency ratio, pulse count in any time interval and accumulating count. General counter can

The following is the verification of general counters, mainly taking the SYN5636 type high precision general counter as an example. The universal counter is equipped with TCXO time base, optional OCXO or rubidium clock, and has the functions of frequency, cycle, frequency ratio, input voltage maximum / minimum / peak value, time interval, pulse width, rise time / fall time, duty cycle and phase measurement function, and powerful mathematical operation, statistics (mean value, standard deviation, maximum, minimum, peak value, count, Allen variance) function.

1. Verification items of general counters

The verification range of the general counter specified in the general counter JJG349-2014 verification regulation is applicable to the first verification, subsequent verification and use check of the universal counter whose frequency measurement range is less than 18GHz.

In the various inspections, the main verification items of general counters are as follows:

In the monitoring department of the general counter appearance, the mechanical damage caused by normal work should not be observed through observation. The control knob and key should be able to work normally. The input socket should be solid and reliable. The front or rear panel should have the name of the instrument, the manufacturer's name or commercial standard, the type of the instrument, the serial number or serial number of the instrument, and the power requirement.

2. Equipment for calibrating universal counters

When the universal counter is connected to the power supply at the time of verification, it is operated according to the instructions, and the self checking and self diagnosis functions of the general counters are checked, and all kinds of measuring functions should be normal. At the time of verification, it carried out project tests in accordance with the verification requirements of the first inspection, subsequent verification, and inspection in accordance with the regulations.

A. reference frequency standard

In the requirement of reference frequency standard, the output signal frequency should be included 5MHz, 10MHz and so on. The frequency stability should be 3 times the frequency stability of the checked universal counter. Other technical indicators, such as the aging rate and frequency accuracy, should be better than the corresponding technical indicators of the universal counter.

We refer to the reference frequency standard equipment used in the verification of universal counter, refer to the SYN3204 GPS tame rubidium frequency standard, receive the GPS signal (optional GPS BD dual-mode), the device itself synchronize the output frequency of the rubidium oscillator in the GPS satellite (optional GPS Beidou dual-mode) cesium atomic clock signal, improve the long-term stability and accuracy of the frequency signal, provide the high precision time frequency standard of the cesium clock magnitude, and is a high-precision frequency standard equipment for the reference frequency standard in the universal counter measurement verification.

Its reference frequency standard function has been verified, which can meet the design requirements of the test, and can be sent to the Metrology Institute for calibration and calibration, with reference to the JJG292-2009 rubidium atomic frequency standard verification regulation.

B. frequency comparison system

When selecting the frequency comparison system, the input signal frequency should be 5 MHz and 10 MHz. The sampling time includes 1s, 10s and so on. The measurement bandwidth should be 5 times the reciprocal of the corresponding sampling time. The ratio uncertainty should be better than that of the corresponding sampling time, and the frequency stability is 3 times.

The frequency counter comparison system of general counters mainly uses the SYN5609 type frequency stability tester, uses the beat method principle to realize the Allen variance measurement, and tests the frequency accuracy and short-term stability of the input frequency standard signal. It is a frequency standard signal time domain measuring ratio instrument.

The function of frequency standard comparison system has been verified, which can meet the design requirements of the test, and can be sent to the Metrology Institute for calibration and calibration, with reference to the JJG545-2015 frequency comparator protocol.

C. synthetic signal generator

Frequency range: to meet the requirement of frequency measurement.

Frequency accuracy: superior to the accuracy of the checked frequency by an order of magnitude.

Level range: to meet the requirements of the checked input level.

Maximum allowable error of level: 0.5dB (0GHz to 1GHz), soil 1dB (1GHz ~ 18GHz).

The synthesized signal generator is a synthetic signal source, which is used to generate the electrical test signals for specific parameters of the circuit under test. The synthesized signal source is not generated directly by the oscillator. Instead, it uses the high stability quartz oscillator as the standard frequency source, and uses the frequency synthesis technology to form any desired frequency signal, which has the same frequency accuracy and stability as the standard frequency source. The output signal frequency can usually be selected according to the decimal digit, which can reach up to 11 digit high resolution.

We have adopted the SYN5651 type signal generator in the synthetic signal generator for the verification of the universal counter. It adopts direct digital synthesis and phase-locked technology. The output frequency is up to 500MHz, and the modulation function is rich.

The function of its synthesis generator has been verified, which can meet the design requirements of the test. It can be sent to the Metrology Institute for calibration and calibration, with reference to the verification regulation of JJG502-2004 synthetic generator.

D. standard time interval generator

Time interval: to meet the requirements of the time interval of inspection.

Frequency accuracy: superior to the accuracy of the checked frequency by an order of magnitude.

Signal form: single output single positive, negative pulse or positive and negative pulse train; two outputs a single positive, negative pulse or positive and negative pulse train.

The signal level can be adjusted continuously in the range of -5V to +5V, and the resolution should be better than 10mV.

In the verification of universal counters, we choose the SYN5612 type time interval generator as a multi-function time synthesizer. With the oscillation period of high stable quartz oscillator as the standard, we use the digital synthesis technology to generate the set of pulse interval, delay time, pulse width and other time interval signals.

Its standard time interval generator function has been verified, which can meet the design requirements of the test. It can be sent to the Metrology Institute for calibration and calibration, with reference to the JJG723-2008 time interval generator verification regulation.

E. power meter

Frequency range: to meet the requirement of frequency measurement.

Level range: to meet the requirements of the checked input level.

Maximum allowable level error: 0.5 dB.

Power is an important parameter to characterize the characteristics of electric signals. The power meter is an instrument for measuring the active power of electric signals. When we test the general counter, we will configure a dedicated power meter to meet the integrity of the whole test system.

3, general counter verification plan

The general counter is a kind of electronic counter with many measuring functions and various uses. It can measure frequency, cycle, time interval, frequency ratio, accumulating count, timing and so on. It can also measure the phase, voltage and so on. It requires that the verification period is not more than one year.

The preceding section mainly introduces the test equipment needed for the verification of universal counters, and describes the parameter requirements that need to be met in the inspection rules, and makes a brief explanation for the verification test equipment. The following is a brief description of the function test of the main system of the general counter.

As for the verification of general counters, many units should set up standards based on project requirements or development requirements. Our company has done a complete set of universal counter verification system, and developed a verification software based on hardware devices.

As shown in the figure, the whole universal counter verification system is mainly divided into four parts: reference frequency standard, verification / test equipment, inspection equipment, verification results; the whole system consists of rubidium atomic frequency standard, frequency standard comparator, synthetic signal generator, standard time interval generator, power meter, general counter, computer and software.

The software system is specially designed for the verification function of universal counters. The whole system is built into an organic carrier, which connects all the hardware systems with software. All the test data are visually displayed by software, which facilitates the registration of data.

At the same time, the scheme of universal counter verification system is in line with the requirements of JJG349-2014 verification regulation for general counters. Xi'an provides all the equipment and software in the whole verification system synchronously.

4. Verification environment of general counters

ambient temperature

It can be selected at a temperature range of (15---30) C. The change of ambient temperature should not exceed +2 C in the verification process, and there should be no abrupt temperature change.

Environmental relative humidity

Relative humidity: less than 80%.

Power supply

AC supply voltage (220 V 10);

AC power frequency (50 s 1) Hz.

There is no normal influence on electromagnetic interference and mechanical vibration.

5. Verification method of universal counter

A. appearance and working normality check

Visually inspect the appearance of the general counter, touch the switches and input sockets, and correctly operate the electricity and operate according to the instructions, which shall comply with the requirements of the regulations. That is, the general counter should not be affected by normal mechanical damage. The control knob and key should be able to act normally. The input socket should be solid and reliable. The front or rear panel should have the name of the instrument, the name of the manufacturer, the trademark, the type of the instrument, the serial number of the instrument or the serial number, and the power requirement.

After switching on the power supply, it will operate normally according to the instruction manual, and the self checking and self diagnosis function of the general counter and all kinds of measuring functions should be checked.

B. built in time base oscillator

The calibration of the universal counter built-in time base oscillator, according to the type and accuracy of the internal oscillator, checks the boot characteristics, daily frequency fluctuation, daily aging rate, 1s frequency stability, frequency repetition and frequency accuracy of the general counter. A general counter with a built-in time base oscillator frequency output, usually referred to JJG180 "quartz crystal oscillator in electronic measuring instruments" or JJG181 "quartz crystal frequency standard" or JJG292 "rubidium atomic frequency standard" for verification.

C. frequency measurement range, input sensitivity and measurement error verification

It should be noted that the output impedance of the synthesized signal generator matches the input impedance of the universal counter. If the input terminal has an attenuator, the decrement is transferred to the minimum position.When the input signal frequency exceeds 1 GHz, the output level error of the synthesized signal generator is required to be less than 0.5 dB, and the insertion loss of the connection line is less than O. 5 dB. Otherwise, the output level is measured by the power meter. The general counter is selected to select frequency measurement function, and the gate time is selected to be 1 s.

The connection is shown in the following figure:

The output signal frequency of the synthesized signal generator is adjusted to the frequency points, and the output level of each point gradually increases from 10mV. Knowing that the general counter is working normally and the reading is stable and accurate, the output level of the synthesized signal generator is the input sensitivity of the verification point; when the power meter is used to measure the output power, the display value is the input sensitivity of the verification point. At the same time, the effective resolution of the display frequency of the general counter is recorded.

The calibration frequency point of frequency measurement is:

The output signal frequency of the synthesized signal generator is transferred to the upper limit of the measurement channel frequency, and the output level is adjusted to the sensitivity that has been measured. The gate time of the general counter is selected 1s and 10s respectively, and each gate time is measured 3 times. The arithmetic average value is taken as the frequency measurement result of the gate time, and the effective resolution is recorded. The measurement error is calculated according to the formula (1):

Delta = 0

Formula:

Delta - frequency measurement error, Hz;

- frequency measurement results, Hz;

0 - synthesis signal generator output signal frequency value, Hz.

The relative error can be expressed as the measurement error.

D. cycle measurement range, input sensitivity and measurement error

It should be noted that the output impedance of the synthesized signal generator matches the input impedance of the universal counter. If the input terminal has an attenuator, the decrement is transferred to the minimum position.When the input signal frequency exceeds 1 GHz, the output level error of the synthesized signal generator is required to be less than 0.5 dB, and the insertion loss of the connection line is less than O. 5 dB. Otherwise, the output level is measured by the power meter. The general counter is selected to select frequency measurement function, and the gate time is selected to be 1 s.

The connection is shown in the following figure:

The output signal cycle of the synthesized signal generator is adjusted to the periodic points listed in Table 4, and the output level of each point gradually increases from 10mV until the checked general counter works normally and the reading is stable and accurate. At this time, the output level of the synthesized signal generator is the input sensitivity of the verification point; when the power meter is used to measure the output power, the display value is the input sensitivity of the verification point. At the same time, the effective resolution of the display frequency of the general counter is recorded.

Calibration period point for periodic measurement

The output signal cycle of the synthesized signal generator is adjusted to 1s, and the output level is adjusted to higher than the measured sensitivity. The gate time of the general counter is selected 1s and 10s respectively, and each gate time is measured 3 times. The arithmetic average value is taken as the periodic measurement result of the gate time, and the effective resolution is recorded. The measurement error is calculated according to the formula (2):

Delta T=T-To

Formula:

Delta T - periodic measurement error, s;

T - periodic measurement results, s;

To - synthetic signal generator output signal cycle value, s.

The relative error Delta T/ To can also be used to indicate the measurement error.

Note: the lPPS signal of rubidium clock or clock must be used as the standard periodic signal.

E. time interval measurement range and measurement error

Starting from the minimum value of measurement, then a measuring point is measured every 10 times in principle until the maximum value of measurement. If the range of the general counter is divided, the lowest gear is selected according to the upper method, and the other files only select the maximum value of the file.

Each check point was measured 3 times (the maximum value was measured 1 times). The arithmetic mean was taken as the measurement result of the point, and the effective resolution was recorded. The error was calculated according to the formula.

Delta t=t-to

Formula:

Delta T time interval measurement error, s;

T one time interval measurement result, s;

To one time interval generator output interval value, s.

The relative error of delta T / to can also be used to indicate the measurement error.

1) pulse width measurement as shown in Fig.

Positive / negative pulse width measurement: time interval generator outputs single or continuous positive / negative pulse signals, and adds two input terminals to the checked universal counter with time interval measurement function. The input slope (positive channel) triggers the slope to be positive / negative, and the input end (stop channel) triggers slope to be negative / positive (according to figure 2 (a) / graph (b)). For a counter with single channel pulse width measurement, the positive / negative pulse signal is selected after the positive / negative pulse signal is added to the channel, and the positive / negative pulse width measurement function is selected (according to figure 2 (b)). The trigger level is usually set at the middle value of the maximum input level and adjusted according to the actual situation.

Block diagram of positive and negative pulse width measurement error

2) two positive / negative pulse interval measurements are connected by graph.

Two positive pulse time interval measurements: the time interval generator outputs two single output or continuous positive / negative pulse signals to two input terminals with the time interval measurement function of the checked general counters respectively, and the triggering slopes of the two input terminals are all positive / negative. The trigger level is usually set at the middle value of the maximum input level and adjusted according to the actual situation.

Two block diagram for measuring error of positive or negative pulse time interval

6, summary

The general quality supervision, inspection and Quarantine Bureau issued the verification regulation of People's Republic of China general specification for measuring and verification JJG349-2014, which clearly stated the verification requirements and verification methods of general counters.

Xi'an is committed to the professional R & D and production of time and frequency industries and devotes itself to the research and development of various time and frequency related test instruments. At present, the SYN5301 type time tester is in line with the JJG237-2010 "stopwatch verification regulation". The SYN5302 type day difference detector is in line with the verification regulation of the JJG488-2008 calibration meter. The SYN5602 type electronic parking timing charging device calibrator meets the JJG1010-2013 "electronic parking time meter" verification schedule and other kinds of time and frequency testing equipment, and has been certified in several national metrology institutes.

Based on the verification regulation of JJG349-2014 general counters, general purpose counter verification has carried out more advanced software input. When used, it can directly display the display results on the computer. It is a set of more complete and convenient system. The efficiency in the long-term verification and utilization has been significantly improved, and its advanced nature will have more room for expansion in the future market.

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