MIL-STD-202H.pdf - 第279页

MI L - S TD - 202 - 30 9 CO NT E N T S PARAGRAPH PAG E FOREW ORD … ………………………………………………………. ii 1. SCOPE 1 1.1 Purpose …… ………………… …………………. …… .. …………. 1 1.2 Precaution s …………………… ……………. ……. . ……. ………. 1 2. APPLICABLE D O C …

MIL-STD-202-309

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.

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MIL-STD-202-309

CONTENTS

PARAGRAPH PAGE

FOREWORD…………………………………………………………. ii

1. SCOPE 1

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

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

2. APPLICABLE DOCUMENTS 1

3. DEFINTIONS 1

4. GENERAL REQUIREMENTS 1

4.1 Procedure…………..…….………………………..….….…..….. 1

5. DETAILED REQUIREMENTS 2

5.1 Summary…………………………………………..…..…………. 2

6. NOTES 2

6.1 Supersession data………………………………………………. 2

iii

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MIL-STD-202-309

METHOD 309

VOLTAGE COEFFICIENT OF RESISTANCE DETERMINATION PROCEDURE

1. SCOPE

1.1 Purpose. Certain types of resistors exhibit a variation of resistance with changes in voltage across the resistor.

This is a measurable characteristic; a test to determine the magnitude of such a characteristic is the Voltage

Coefficient of Resistance Determination Procedure.

1.2 Precautions. Adherence to 4.1, applying voltage intermittently for not more than the total of 0.5 seconds in any

5 second interval is emphasized as an important consideration of this method. Failure to comply would result in a

voltage coefficient of vast variations. A resistance measuring device capable of withstanding high voltage

applications should be used. Certain types of resistors exhibit a variation of resistance with changes in potential

difference, this effect being separate and distinct from the change in resistance due to heating effect whether from

applied voltage or ambient conditions.

2. APPLICABLE DOCUMENTS

This section not applicable to this standard.

3. DEFINTIONS

This section not applicable to this standard.

4. GENERAL REQUIREMENTS

4.1. Procedure. The voltage coefficient is applicable only to resistors of 1,000 ohms and over. Unless otherwise

specified in the individual specification, all measurements and tests shall be made at a temperature of 25°C ±5°C.

Adjust the resistance measuring device to apply 0.1 X rated continuous working voltage to the resistor. Measure the

resistance by applying this voltage intermittently for not more than the total of 0.5 second in any 5 second interval.

Readjust the resistance measuring device to apply 1.0 X rated continuous working voltage to the resistor and repeat

the above intermittent measuring procedure. Compute the Voltage Coefficient (VC) as follows:

9.0

100)( −

Where:

R = Resistance at rated continuous working voltage.

r = Resistance at 0.1 rated continuous working voltage.

E = Rated continuous working voltage.

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