MIL-STD-202H.pdf - 第268页

MI L - S TD - 202 - 308 CO NT E N T S PARAGRAPH PAG E FOREW ORD … ………………………………………………………. ii 1. SCOPE 1 1.1 Purpose …… ………………… …………………. …… .. …………. 1 1.2 Precaution s …………………… …………. ……. ……. . …………. 1 1.3 Checks for c o nf…

MIL-STD-202-308

FOREWORD

1. This standard is approved for use by all Departments and Agencies of the Department of Defense.

2. This entire standard has been revised. This revision has resulted in many changes to the format, but the most

significant one is the splitting the document into test methods. See MIL-STD-202 for the change summary.

3. Comments, suggestions, or questions on this document should be emailed to std202@dla.mil or addressed to:

Commander, Defense Logistics Agency, DLA Land and Maritime, ATTN: VAT, P.O. Box 3990, Columbus, OH

43218–3990. Since contact information can change, you may want to verify the currency of this address

information using the ASSIST Online database at https://assist.dla.mil.

北测（上海）电子科技有限公司

联系方式：xuyj@beice-sh.com 13917165676

MIL-STD-202-308

CONTENTS

PARAGRAPH PAGE

FOREWORD…………………………………………………………. ii

1. SCOPE 1

1.1 Purpose………………………………………….……..…………. 1

1.2 Precautions……………………………….…….……..…………. 1

1.3 Checks for conflicts………………..……………………………. 1

2. APPLICABLE DOCUMENTS 1

3. DEFINTIONS 2

4. GENERAL REQUIREMENTS 2

4.1 Apparatus……………….…….……..…………….….........……. 2

4.1.1 Test system............................................................................ 2

4.1.1.1 DC measurement considerations…….………………..………. 2

4.1.1.2 AC measurement considerations….…………………..………. 2

4.1.1.3 Calibration technique…………………..…………………….…. 2

4.1.2 Synopsis…….….…….………….………….………...…………. 2

4.2. Procedure…………….………………………..….….………….. 3

4.2.1 Operating conditions………………………..……..……………. 3

4.2.2 Measurements…….……………………………….…………….. 3

4.2.2.1 Calibration….……………………………………….…………….. 3

4.2.2.2 System noise (S)…………………………………..…………….. 5

4.2.2.3 Total noise (T)………....…………………………..…………….. 5

4.2.3 Determination of the "microvolts-per-volt-in-a-decade" index.. 6

4.3 Errors…………………………………………………………….. 6

5. DETAILED REQUIREMENTS 8

5.1 Summary…………………………………………..…..…………. 8

5.2. Examination and measurements…………………………....…. 8

5.2.1 Marking resistance to solvents…….……………..……………. 8

5.2.2 Component protective coating, encapsulation material

and sleeve material resistance….……………..………………. 8

6. NOTES 8

6.1 Supersession data………………………………………………. 8

FIGURES PAGE

1. Block diagram of system …..……………………….……………………… 3

TABLES PAGE

1. Standard operating conditions …..………………….……………….…… 4

2. Correction factor for presence of "system noise".………………….…… 7

iii

北测（上海）电子科技有限公司

联系方式：xuyj@beice-sh.com 13917165676

MIL-STD-202-308

METHOD 308

CURRENT-NOISE TEST FOR FIXED RESISTORS

1. SCOPE

1.1 Purpose. This resistor noise test method is performed for the purpose of establishing the "noisiness" or "noise

quality" of a resistor in order to determine its suitability for use in electronic circuits having critical noise requirements.

This method is intended as a standard reference for the determination of current noise present in a resistor, for use in

an application with specific current-noise requirements. It is not intended as a general specification requirement.

Interference caused by the generation of spurious noise signals in parts tends to mask the desired output signal, thus

resulting in loss of information. For low-level audio frequency and other low-frequency circuits, where low-noise parts

are used, resistors may become an important source of interfering noise. One source of noise in a resistor is

molecular thermal motion which generates a fluctuation voltage termed "thermal noise". It is not necessary to

determine the magnitude of thermal noise by measurement since the mean-square value of the fluctuation voltage is

predictable from Nyquist's equation, which shows the mean-square value to be proportional to the product of

resistance, temperature, and the pass band of the measuring system. Generally, an increase in fluctuation voltage

appears when direct current (dc) is passed through resistive circuit elements. The increase in fluctuation voltage is

termed "excess noise" or "current noise". The magnitude of current noise is dependent upon many inherent

properties of the resistor such as resistive material and other factors such as processing, fabrication, size and shape

of resistive element, etc. Since there is no apparent functional relationship between current noise and many of these

factors, current noise generally cannot be predicted from physical constants. Therefore, it is necessary to measure

current noise to determine its magnitude. The method employed in this test has been designed to evaluate

accurately the "noisiness" or "noise quality" of individual resistors in terms of a noise-quality index. The noise-quality

index, expressed in decibels (dB), is a measure of the ratio of the root-mean-square (rms) value of current-noise

voltage, in microvolts (µv), to the applied dc voltage, in volts. The pass band associated with the noise-quality index

is one frequency decade, geometrically centered at 1,000 hertz (Hz). This index is termed the "microvolts-per-volt-in-

a-decade" index. In the design of circuits, an added advantage accrues from the definitiveness of the index which

allows the estimation of interference attributable to current noise. Conversely, for a given limit of current-noise

interference in a particular circuit design, a maximum acceptable value of the index may be established. Ordinarily, it

is not necessary to duplicate the operating conditions of the particular circuit design when measuring the current

noise. The noise quality of populations of resistors may be reasonably estimated by measurement of the index of

representative groups of resistors using suitable sampling procedures. Measurements on sample groups tend to

have a normal distribution and once representative parameter values for the distribution have been established (the

mean and standard deviation), such parameter values would serve as norms in judging "noisiness" and product

uniformity insofar as noise is concerned.

1.2 Precautions. Adherence to the ambient temperature specified in 4.2.1 is emphasized as an important

consideration of this method. It is also necessary, in making noise measurements, using the apparatus of this

method, to delay reading the noise meter for a period of time no less than four times the effective time constant of the

detector to allow the meter sufficient time to reach at least 98 percent of the representative average value. The

effective time constant of the apparatus is normally adjusted to a value close to 1 second and therefore, a minimum

time delay of 4 seconds is normally required for the noise meter to indicate a valid average. Immediately after this 4

second delay, the meter should be read even though it continues to fluctuate as the noise signal varies. Normally,

the operator in making a visual reading of the fluctuating meter pointer, should estimate an average for a short

duration, in the order of 1/2 to 1 second.

1.3 Checks for conflicts. When this test is referenced, care should be exercised to assure that conflicting

requirements, as far as the properties of the specified finishes and markings are concerned, are not invoked.

2. APPLICABLE DOCUMENTS

This section not applicable to this standard.

北测（上海）电子科技有限公司

联系方式：xuyj@beice-sh.com 13917165676