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1、 - _ . I . - EIA 421-A 3 3234b00 0068345 O W U I ANSI/EIA RS-421-A-1983 APPROVED JANUARY 3, 1983 O S I A STANDARD EIAINARM STANDARD FOR DRY REED SWITCHES RS-42 1-A (Revision of RS-421) MARCH 1983 Engineering Rep Low Air Pressure IEC 68-2-14 Testr N: Change of Temperature IEC 68-2-17 IEC 68-2-20 Tesi
2、 Q: Sealing Test T: Soldering IEC 68-2-ZOA First Supplement: Test Tb: Resistance to- Soldering Heat, Method 1 Copyright Electronic Components, Assemblies bounce usually implies the motion resulting from contact impact. Bounce Time (IEC) The interval of time between Che instant of the first physical
3、closing (or opening) and the instant of the final physical closing (or opening) of a reed contact unit. Br ea k-Be f o r e-Ma ke Contact which interrupts one circuit before closing another circuit; Form C. W e w i t of conta built up be tween between themc metallic protrusion or brjdge is es to caus
4、e an electrical path (2) A form of conta inductance circu and resolidifyin of bridge. the break of a low voltage, low aration, that results in melting e form of a metallic protrusion (3) Make-before-break action, as when a wiper touches two successive cont eously while moving from one to the other.
5、Chatter, Contact The undesired inter contacts. It may o when the switch is osure of open contacts or opening of closed the switch is operated tir released, or ernal shock or vibration. a Copyright Electronic Components, Assemblies magnetic lines of force across this gap cause contact elosure. Hyster
6、esis The amount of magnetization of a ferrous material, lags the magnetizing force due to molecular reluctance. Insulation Resistance The resistance of the glass body of the switch. Measured with an electrometer with the switch deenergized. Latching Contacts (Bistable) Contacts that lock in either p
7、osition until reset. Normally Closed (NC) Contacts See Form B. Normally Open (NO) Contacts See Form A. Operate The condition attained by a switch when all contacts have functioned, Operate Time See Time, Operate. Operate Time (Total) Form A Contact - The total elapsed time from the instant power is
8、applied to the energized quantity urd1 the contact has functioned and all contact bounce has ended, Form B Contacts - Thetotal elapsed time from the instant power i s removed from the energizing quantity until the contact has functioned and all. contact baunce has ended. * See Pickup Value- Qperate
9、Value, Must (IEC) The stated limit of the applied energized quantity at which the reed contact unit shall physically -operate (ii-t ese charkwterlstias Eire not normally tested for during lot inspection and are considered to be relatively uniform for any given switch type. .AAfthough not intentional
10、ly alterable -without modifying the basic des witch, there is a rangeaof variationthat does exist, and while t characteristics are normally specif ied by the manufacturer Cas l.or maximum values), in some cases a value within the normal range ban be specified and supplied. , - Y Copyright Electronic
11、 Components, Assemblies three-dimensional foreign material or burrs that cannot be moved are cause for rejection only if they are in the contact area, 5.2.2.9 Any visible moisture or condensation within the capsule is cause for rejection. 5.2.2.10 Interior reed plating shall be free from corrosion,
12、peeling, and flaking. Discoloration or stains are not rejectable unless visible to the unaided eye or in the contact area. The nominal mass shall be determined if so required by the Detail Specification. 5.2.3 OPERATIONAL PARAMETERS Pickup, Dropout, Contact Resistance, Dwell (Single Pole - Double Th
13、row, SPDT) 6.1 General All switches procured in accordance with this specification, or a detailed drawing shall have been 100% sorted for the proper pickup range, minimum dropout, and contact resistance specified herein or on the detailed drawing. The specified AQL shall apply to these parameters co
14、nsidered collectively. Each switch type should be tested using the standard test coil specified in paragraphs 19.3 and 19.4, so that the values of pickup or dropout obtained may be directly compared by the supplier and user. An example of this is that a sample IA switch (19.3) when tested using Stan
15、dard Coil I may exhibit an operate of 30 ampere turns (At) and .a release of 18 At; but when tested using Standard Coil II, shows a 44 At operate and 31 At release point. It is important to note that the pickup and dropout values obtained from testing a given component will change if the ferromagnet
16、ic leads of the device are cut to some length other than the manufacturers standard. The overall length of the defined standard switches is not specified in this document because the lengths vary somewhat from manufacturer to manufacturer. Each manufacturer must provide a curve plotting pickup value
17、 vs. cut length for any switch provided under this Standard so as to allow the user to correlate sensitivity values of devices obtained from different sources. A sample cut switch curve is provided as a guide in the application notes with an explanation as to its use. Care must be taken in obtaining
18、 accurate pickup or dropout values. A shift of the contact gap away from the center line of the coil winding will produce an apparent rise in pickup. Earths magnetic field will add to or subtract from the apparent pickup if the coil axis is parallel to the local earth field rather than perpendicular
19、 to it. Since the reed material does exhibit minor hysteresis after being acted on by a magnetic field, saturation of the reeds with a known polarity field is required to erase reed history and obtain correlatable pickup or dropout values. The reed contact unit may be demagnetized prior to testing i
20、f it is of the remanent variety. Copyright Electronic Components, Assemblies - 1 ampere-turn per millisecond for must-not-release, must- release, must-not-operate and must-operate values. Test leads and their clips, when attached to a dry reed switch under test, must be non-magnetic. Magnetic fields
21、 and materials should be kept a sufficient distance from the switch under test to make effects incon- sequential (less than 0.5 ampere-turn or 2%, whichever is higher). This applies regardless of contact form. Contact loads for these measurements shall be .O50 V dc, 10 mA for low level type switches
22、 (Level I rating) and 6-12 V dc, 10-100 mA for all other types. Accuracy of measurement equipment shall be +3% of full scale for At and +5% for contact resistance. Certain switches rated and intended for use niy on power loads may utilize higher test voltage or currents, but these conditions must be
23、 listed on the manufacturers Detail Cpecif ication. 6.2 Procedure 6.2.1 Measurement - Form A Switches The reed switch shall be characterized after magnetic saturation. Because of possible asymmetries in the reed switch and test set, the reed switch is characterized in both polarities of test coil cu
24、rrent. 6.2.1.1 The reed switch shall be placed in the standard test coil with the magnetic gap centered in the coil winding and the longitudinal coil and switch axis perpendicular to the local earths magnetic field. The coil is then energized sufficiently to magnetically saturate the reed material a
25、fter which the coil drive is reduced to zero. The coil drive is then increased until the normally open contacts close; this value is the first pickup. Coil drive is then increased 25% or 10 At, whichever is greater. Coil drive is then reduced to zero. The ampere-turn value on the decrease at which t
26、he normally open contacts open is the first dropout. Coil polarity is then reversed and drive increased to saturation and then.reduced to zero. Coil drive is then increased until switch contacts close; this is the second pickup. Coil drive is again increased 25% or 10 At, whichever is greater, then
27、reduced to zero; during this decrease the second dropout is increased. Copyright Electronic Components, Assemblies e method that will allow the buyer to make an accurate determination of the true dielectric strength of a reed switch. Both methods utilize preioni- zation of the internal atmosphere of
28、 the switch. The preionization technique of the standard method is independent of the operator, but that of the alternate is somewhat subject to the control of the operator and the ambient illumination. When using the alternate method, care must be exercised to obtain maximum accuracy and uniformity
29、. Accuracy of measurement shall be - +3%. Procedure 7.2.1 The standard test procedure for dielectric strength is conducted by placing the switch to be measured in a suitable holding fixture with the switch electric gap in close proximity and parallel to a radioactive or other suitable ionization sou
30、rce. The ionization source must induce preionization to ensure that the first gap breakdown will be the correct value for dielectric strength. A Strontium 90 source having a minimum radiation level of 80 micro curies with the gap of the contact located in line with the source window at a maximum dis
31、tance of one inch is satisfactory. The voltage source shall be sinusoidal, 45 Hz to 65 Hz, with less than 5% distortion. The voltage shall not drop more than 5% when the load is increased from zero (O) to 100 pA. For go/no-go testing with the switch inserted into the test fixture, the selected level
32、 of test voltage is instantaneously applied to the test switch and the leakage current is monitored. The indicator used to detect failures shall have a response time of 25 milliseconds (ms) maximum at a current of 100 PA. It shall be adjusted to operate when the leakage current exceeds 100pA. Accept
33、ance or rejection shall be based on 100 PA leakage current using instantaneous application or test voltage. .Duration of test is not less than 1 second. For evaluation testing for actual breakdown value, the test voltage is increased gradually until arcing or breakdown occurs or leakage current incr
34、eases to 100 PA. Copyright Electronic Components, Assemblies 0.r for evaluation testing, voltage is increased to the breakdown value. CAUTION Care must be taken to prevent damage to contact surfaces during arcing period. Reduced switch life or increased contact resistance may result depending on the
35、 type of switch and the current limitations of the testing equipment. Preferably, the arcing current should be limited to one pA or less. 8.0 OPERATE, BOUNCE, RELEASE AND TRANSFER (SPDT) TIME 8.1 General This test method specifies the procedure to be used in the measurement and evaluation of the pri
36、ncipal dynamic characteristics of a reed switch using an oscilloscope. Because of the nature of the characteristics, they are inherently somewhat dependent upon the controlling magnetic field; thus, to a large degree, the measured values will be dependent upon coil configuration, overdrive level, an
37、d actuating speed. Therefore, when attempting to measure and correlate these characteristics, it is very important to operate the switch under identical conditions. Accuracy of measurements shall be - +3%. 8.2 Procedure 8.2.1 The reed switch is placed in the test coil with the magnetic gap cantered
38、in the coil winding, The longitudinal axis of the test coil and test switch shall be vertical. The following operational parameters shall apply: test switch contact load shall be .O50 V dc, 10 mA for dry circuit and low level switches, or 6 V dc, 10-100 mA for all other types; coil drive shall be le
39、ss than five cycles per second with single pulse operation preferred, coil overdrive shall be adjusted to the pickup value plus 50%; oscilloscope connections shall be as shown in Figure 4. 8.2.2 Operate time is measured by setting oscilloscope time base to trigger on the leading edge of the coil dri
40、ve pulse, and is measured from the instant of coil energization to the instant of the first contact closure of the last contact to function. Copyright Electronic Components, Assemblies or 6 V dc, 10-100 mA for all other types; coil drive shall be less than 5 Hz with single pulse operation preferred,
41、 coil overdrive shall be adjusted to. the pickup value plus 50%; oscilloscope connections shdl be s shoivn in Figure 5. Solid lines show the connections normally open contact transfer time and the broken line for measuring normally open to normally- closed contact transfer time. Cpecif ication. , -
42、-. Copyright Electronic Components, Assemblies an aluminum cube with the test coil encapsulated into a cavity is ideal. Switch mounting in the test coi1 shall be by means of rubber spacers to force glass capsule securely against either top or bottom of coil bobbin. UBBER BAND SWITCH FIGURE 6 MOUNTIN
43、G FIXTURE Switch leads shall be firmly attached to insulated support terminals by soldering or other suitable method _- as close as practical to the body of the switch. Copyright Electronic Components, Assemblies to standardize other similar coils by using Tive switches selected per above and .estab
44、IiShing cbrrelation between standard -cori and cai1 under test, -Cails may be used es secondary standards if they *correlate to e primay standard .cai1 within + -2 At or - + 1% (whichever is greater) for -all iformly divide and span the range intended for standard, as statistical base. ,ln each coil
45、 using technique described calibration purposes. values .af :swttdh alosure measured. . . _- . - - “ Copyright Electronic Components, Assemblies & Materials Association Provided by IHS under license with ECA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/29/2007 02:17:51 MDT
46、No reproduction or networking permitted without license from IHS -,-,- _- E I A 42L-A 3 m 3234600 00b8397 m RS-421-A Page 50 27.0 APPLICATION NOTES The following Section is intended to be used as a guide for the application of reed switches in various end products. Information is for most part gener
47、el in nature, but can help prevent misapplication or use in marginal situations. Proper use of the data can guide the user in design of his product and minimize attendant costs. 27.1 Cutting of Leads and Effects on Pickup Cutting the leads of a reed switch removes low reluctance iron and introduces
48、high reluctance air into the magnetic circuit, much the same as adding resistance to an electrical circuit. The result is that a greater number of equi,valent ampere turns is required to close a switch of a given sensitivity after cutting. Figure 12 illustrates typical results. EFFECT OF CUTTING ON
49、PICKUP STANDARD LENGTH TO MINIMUM TRIM LENGTH LEADS CUT SYMMETRICALLY ABOUT THE GLASS PICKUP RANGE: 17.5 - 52.5 A t e 3 e OVERALL SWITCH LENGTH (INCHES) FIGURE 12 All suppliers furnishing switches to this Standard must provide a curve similar to the above for each switch type. A user may then compare sensitivity values of various manufacturers for corresponding length switches. Copyright Electronic Components, Assemblies & Materials Association Provided by IHS under license with ECA Licensee=IHS Employees/1111111