Metrological provision Means of Measurement Technic (MMT) for measuring frequency of infosignals

 

The purpose of the work

1.1 Preview of the scientific, legal and technical basis of metrological support of MMT for measuring the frequency.

1.2 Examine methods of verification of electronic frequency counters (EFC) and metrology operations for verification.

1.3 Acquire practical skills for the verification of EFC.

 

Key statements

2.1 EFC verifiable characteristics.

Subject to verification are the following parameters:

- the range of measured frequency sinusoidal and pulse signals

-the error of measuring the frequency

-the frequency range in the measurement period, sinusoidal and pulse signals

-the period of measurement error

-the measuring range of the frequency ratio

-error measuring ratio of frequencies, etc.

2.2 Means of measurements used for calibration.

When checking EFC, the following reference and auxiliary means of verification:

- receiver reference frequencies

- rubidium frequency standards with nominal values ​​of the frequencies of 100 kHz, 1 and 5 MHz with the relative instability of 10^-11-

- quartz-crystal generator with the same values ​​of nominal frequency and the relative instability of the order of 10^-8

- frequency standards and quartz-crystal generators are measures of the standard frequency, and if there is a possibility and necessity, the accuracy of these measures is controlled by the receiver reference frequencies

- frequency synthesizers, covering the frequency range 0.01 Hz -50 MHz

- Frequency Multipliers

- Frequency Comparators

- universal generators, voltmeters, oscilloscopes, and AC voltage.

2.3 Conditions of verification and preparation for it.

In carrying out verification operations subject to the following conditions:

- the unit that came in fact, subjected to external examination. We should pay attention to the availability, serviceability and cleanliness of the entire property, the condition of paint and clear labeling. The presence of dirt and rust is unacceptable. The instrument must not be mechanical damage that could affect its operation, such as looseness of control knobs, damaged terminals, poor fixation switches

- devices having a fault, in actual fact are not accepted.

- Verification of device parameters is performed at a nominal supply voltage under normal conditions:

- ambient temperature is 293 ± 5 ° K (20 ± 5 ° C)

- Relative humidity of 65 ±15%, atmospheric pressure is 100 ± 4 kN / m² (750 ± 30 mm. Hg. Art.)

- Voltage Mains 220 V ± 4,4 V.

Before the operations of checking, you must make the following preparations:

- place the unit under verification in the workplace, providing comfort and eliminating getting it out of direct

- connect wire terminals that are under verification and reference devices used for verification, to the ground bus,

- to make a connection, the device under verification to model devices with regular cables and adapters;

- connect devices to an AC voltage of 220, 50Hz

- plug-in devices to the network and give them a warm-energized for 1 hour.

2.4 Transactions verification.

Visual inspection

When conducting an external examination must be verified: the

● absence of mechanical damage, affecting the accuracy of the readings, the

● presence and strength of attachment of controls and switching, the clarity of fixing their positions, smooth rotation of knobs settings;

● arrows showing the correct installation of devices against the zero marks of the scale,

● the purity of sockets, connectors and terminals

● the state of wires, cables, adapters,

● paint condition and clarity of markings

● the absence of detached or weakly attached circuit elements and foreign objects (defined by ear when bending device).

If the appliance defects, due verification shall be cancelled and direction for repair.

Testing

Verifying the device in the "Self-control" mode on the device control frequencies.

Calibration range of measured frequencies and periods of

Verification range of measured frequencies and periods is carried out according to the scheme shown in Fig. 1, by direct measurement of the frequency (period), given by the measuring generators (MG) of the respective ranges and types.

Measurements were carried out at both ends of the range of frequencies f _n (T_n) and f _in (T_s) and 5- 6 points within range. If necessary, check the minimum values ​​of the input voltage to the output of the generator voltmeter connected by means of which, and establish the minimum voltage input signal. At the same time observed EFC has to have stable results.

 

Figure 1 – Calibration frequency bands (periods) by the method of direct measurements.

The basic definition of the relative error of frequency measurement is performed according to the expression:

	,	(1)
	,

 

where ;

δ_qg – the relative error of the reference oscillator,

T _count – measurement time (time accounts);

f _s – measured frequency.

 

Determining the relative error of the measurement period is made ​​according to the

	,	(2)
	,

 

where ,

T _qg – the period of the reference oscillator signal,

T_c – as measured by the period;

n = 10^ν, ν = 0, 1, 2, 3, 4,.... – a multiplier signal period;

m = 10^ε ε,= 0, 1, 2, 3, 4,.... – frequency multiplier of crystal oscillator.

 

In determining the errors of δ _f and δ _T is checked separately:

- the relative error of the reference frequency crystal oscillator (δ_qg)

- components of the measurement error due to the frequency and period of discontinuity (the second terms in equations (1) and 2)).

 

Determination of the relative error by the reference frequency of quartz-crystal generator

Relative accuracy of the reference oscillator frequency is determined by comparison with the comparator circuit shown in Fig. 2.

 

Figure 2 – Determination of the relative error in frequency reference oscillator by comparison

Output of the reference oscillator under verification EFC connected to the input of a comparator. Frequency of the source model, which is the standard rate n₁-type, the signal of the same frequency at the input of the comparator 2 and the connector "5 MHz" frequency of type H3, which uses this signal instead of its own reference clock signal.

And the comparator output signal frequency f _t is input auxiliary EFC, operating in the frequency measurements at a measurement time of 1 or 10 sec.

To improve the reliability of measurement results is removed at least 10 consecutive readings of the frequency and is their average value:

 

,

(3)

 

where f_ci – a frequency output of the comparator unit of measurement;

n – the number of single measurements carried out.

 

Relative error of the reference oscillator frequency is determined by the

 

,

(4)

 

where f _c – value of the frequency comparator corresponding to the nominal value of the reference frequency generator;

f _n – nominal frequency of the reference oscillator.

Appendix B shows the NMC frequency standardЧ1-53, the frequency comparator Ч7-12 and frequency synthesizer. In carrying out laboratory work rather than the above model can be used similar devices on the NMC devices.

Determining the relative error δ_qg, shall adjust the frequency of the reference oscillator EFC, after which the slot "frequency correction" sealed.

Determination of components of the error of the measured frequency and period due to the discreteness of the account

Definition data components of the error is carried out by direct measurement of the standard frequency. The source of the reference frequency is used, or a frequency synthesizer or synthesizer with frequency multiplier.

Circuit connection of devices with the operation of verification is given in Figure3.

The synthesizer must be synchronized with verifiable EFC from the reference oscillator device under verification.

The input signal is fed under verification EFC, close to the upper limit frequency and a voltage equal to the minimum input voltage at which the EFC should work fine. In the absence of a graded synthesizer voltage output signal, it is necessary to control the voltage with a voltmeter.

Carry out a series of 10 observations. The results of calibration are considered positive if the 9 cases (reading) the measurement does not differ from f _qg more than ± 1 division accounts.

 

 

Figure 3 – Determination of discrete error consistent.

 

 

For a similar procedure is determined by the component of error due to the discreteness of the measurement period. In this case the input frequency is served frequencies corresponding to the upper and lower frequency range specified for the frequency measurement mode period.

 

 

Key issues

3.1 Define the term "MMT tests."

3.2 How to calibrate (calibration work) EFC.

3.3 State the definition of verification EFC.

3.4 Types of calibration and calibration interval?

3.5 What major are determined by checking the MX EFC?

3.6 List of measuring instruments used in checking EFC.

3.7 Specify the operations during the verification EFC.

Homework

4.1 Examine the basic provisions relating to the verification and calibration of the electronic frequency counter (EFC).

4.2 Write down the metrological characteristics of the frequency comparator.

4.3 Write down the metrological characteristics of a frequency standard.

4.4 Write down the metrological characteristics of the frequency synthesizer.

Laboratory reference

5.1 Familiarize with an equipment in the workplace, collect a measuring chart in obedience to lines. 1 and prepare devices to work.

5.2 In the mode of measuring of frequency define the threshold of sensitiveness (minimum tension which will provide a proof show on a board) and conduct the check of device on the indicated frequencies at tablas. 5.1.

5.3 To expect an absolute error the measured and maximum possible error, it is got results to write down at tablas. 5.1.

(δ_i - choose from passport information of the set generator)

Table 5.1 Verification of the range of measured frequencies

f rkHz	Tc	U min	results on the board	absolute error Δ = F and – f r	maximum permissible error Δi = δi · f i	Output
0.1

 

 

5.4 In the mode of measuring of period to conduct the analogical measurings and calculations. To present results as table. 5.2.

 

 

Table 5.2 Calibration of the measured range of periods

f rkHz (Tr)	T m	n	results on the board	U min	absolute error Δ = T and – T r	maximum permissible error Δi = δi · T i	output
0.1

 

 

5.5 Using technical descriptions of the set cymometer, to choose time of account which provides the least error in the mode of measuring of frequency.. 5.3.

Possible δ in the mode of frequency will expect after a formula 1.

 

Table 5.3 Determination of the relative error of frequency measurement (error discrete)

f i,kHz	T count	results on the board	absolute error Δ = ± 1 / T, count	N	δ	Allowable δ	Output
0.1

 

 

5.6 Using technical descriptions of the set cymometer, to choose the parameters of the mode of measuring of period so that to provide the least error of measuring of period.. 5.4.

Possible δ in the mode of period will expect after a formula 2.

 

Table 5.4 Determination of the relative error of measurement period (error discrete)

f rkHz (Tr)	T m	n	T cq	results on the scoreboard	absolute error Δ = ± T m / n	N	δ	Allowable δ	Output
0.1

 

6. Protocol of the laboratory work (№.... name...)

6.1 The purpose of the experiment.

6.2 List of equipment used in the Table. 6.1.

 

Table 6.1 - List of equipment used

Name of the device	type	serial number	Metrological characteristics
Accuracy	Range	Frequency

 

6.3 Scheme of the measurement

 

 

 

Type of calibrated frequency counter____________________________________

Visual inspection_________________________________________________

Testing_________________________________________________________

 

Calibration settings

 

Ambient temperature ___________________________________ ° C

Relative humidity __________________________________

Pressure mmHg_________________________________________

Time of pre-heating ____________________________________ min.

Supply voltage _________________________________________________ V.

The frequency of voltage _________________________________________ Hz.

 

6.4 Based on these results to draw conclusions about the verification carried out by frequency.

Verification Measurement frequency range investigated EFC _________

Conclusion:

Calibration of the measured range of periods studied EFC _________

Conclusion:

Determination of the relative error of measurement of the frequency of the EFC __________

Conclusion:

Determination of the relative error of the measurement period studied EFC __________

Conclusion:

The overall conclusion

is made ​​__________________________ Checking "___" _________ 20 __ y.

Name

 

Protocol tested: (Signature)

Individual task