MIL-STD-202H.pdf - 第296页
MI L - S TD - 202 -3 11 CO NT E N T S PARAGRAPH PAG E FOREW ORD … ………………………………………………………. ii 1. SCOPE 1 1.1 Purpose …… ………………… …………………. …… .. …………. 1 2. APPLICABLE D O C U M EN T S 1 3. DEFINTIONS 1 4. GENERAL RE Q UI R E…
MIL-STD-202-311
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-202-311
CONTENTS
PARAGRAPH PAGE
FOREWORD…………………………………………………………. ii
1. SCOPE 1
1.1 Purpose………………………………………….……..…………. 1
2. APPLICABLE DOCUMENTS 1
3. DEFINTIONS 1
4. GENERAL REQUIREMENTS 1
4.1 Apparatus…………..……………………….……..….….…..….. 1
4.1.1 Test circuit…..……………………………..….….…………..….. 1
4.1.2 Monitoring apparatus……………………..….….…………..….. 2
4.2. Procedure…………………………………..….….…………..….. 2
5. DETAILED REQUIREMENTS 2
5.1 Summary…………………………………………..…..…………. 2
6. NOTES 3
6.1 Supersession data………………………………………………. 3
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北测（上海）电子科技有限公司
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MIL-STD-202-311
METHOD 311
LIFE, LOW LEVEL SWITCHING
1. SCOPE
1.1 Purpose. This test is conducted for the purpose of determining electrical contact reliability under low-level
switching conditions in the environment in which the contacts operate. A low level switching circuit is one in which
the voltage and stored energy are sufficiently small so that the resistance of a pair of contacts is not affected by
electrical phenomena associated with the electrical current flow or the switching. Such a circuit is also one where the
voltage or the current is too low to cause any physical change in the contacts; contact resistance can only be affected
by changes in the contacts caused by mechanical action on the contacts. Electrical loads, which result in arcing
across electrical contacts, affect contact surfaces in many ways, mostly favorable to reduction of contact resistance,
since insulating films and small rough raised areas on the contact are burned away or melted down, to reform as a
more even and larger contact surface. Under low-level conditions, the advantages, as well as the occasional
disadvantages of this arcing will be absent. If low-level loads and intermediate or power loads are to be applied to
different pairs of contacts on the same component part simultaneously, reliability of the low-level conditions can be
impaired due to deposition of foreign materials resulting from vaporization surrounding the contacts operating at
larger loads in the same enclosure or in an adjacent area, because of this fact, and because low-level contacts may
develop films as a function of their environment, the contacts are tested in an environment similar to that in which
they are used. This test in no way reflects the contact capability in the intermediate or "minimum" current area and
shall not be considered as a substitute for testing in this area when specified.
2. APPLICABLE DOCUMENTS
This section not applicable to this standard.
3. DEFINTIONS
This section not applicable to this standard.
4. GENERAL REQUIREMENTS
4.1. Apparatus.
4.1.1 Test circuit. Monitoring of the contact resistance of each pair of contacts shall be accomplished on each
cycle. A separate monitoring indicator shall be used for each pair of contacts. The apparatus, which cyclically
operates the contacts, shall be capable of automatically cycling the contacts at the rate specified. The power source
for the open-circuit voltage shall not exceed 30 millivolts dc maximum or peak ac at 10 milliamperes (mA) maximum.
Open-circuit voltage is defined as the voltage that would appear at the contacts, when the circuit is energized and
when the contacts are open. One means of generating this voltage is to pass a stable adjustable current through a
low-ohmage resistor (such as a shunt resistor for an ammeter). This means will provide the low impedance, low
voltage, controllable, and well defined voltage source necessary. The current shall be adjusted so that the current
through the pair of contacts, when closed is limited to 10 milliamperes, maximum.
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