西門子1FK7伺服電機維修作為一種數字式執(zhí)行元件，在運動控制系統(tǒng)中得到廣泛的應用。在使用西門子電機的時候，感覺電機工作時有較大的發(fā)熱。實際上發(fā)熱是電機的一個普遍現(xiàn)象，但怎樣的發(fā)熱程度才算正常，以及如何盡量減小步進電機發(fā)熱呢?

　　1、將西門子電機發(fā)熱控制在合理范圍內、1FK7042-5AF71-1TH0維修
　　電機發(fā)熱允許到什么程度，主要取決于電機內部絕緣等級。內部絕緣性能在高溫下(130度以上)才會被破壞。低于130度，電機不會損壞，表面溫度會在90度以下。表面溫度在70-80度都是正常的。滴幾滴水迅速氣化，則90度以上了;當然也可以用測溫槍來檢測。
　　2、西門子電機發(fā)熱隨速度變化的情況
　　采用恒流驅動技術時，電機在靜態(tài)和低速下，電流會維持相對恒定，以保持恒力矩輸出。速度高到一定程度，電機內部反電勢升高，電流將逐步下降，力矩也會下降。
　　3、發(fā)熱帶來的影響
　　電機發(fā)熱雖然一般不會影響電機的壽命，對大多數客戶來說沒必要理會。嚴重的發(fā)熱會帶來一些負面影響。如電機內部各部分熱膨脹系數不同導致結構應力的變化和內部氣隙的微小變化，會影響電機的動態(tài)響應，高速會容易失步。
　　4、減少電機的發(fā)熱
　　減少發(fā)熱，就是減少銅損和鐵損。 減少銅損有兩個方向，減少電阻和電流，這就要求在選型時盡量選擇電阻小和額定電流小的電機，對兩相電機，能用串聯(lián)的電機就不用并聯(lián)電機。細分驅動器由于電流波形接近正弦，諧波少，電機發(fā)熱也會較少。 減少鐵損的辦法不多，電壓等級與之有關，高壓驅動的電機雖然會帶來高速特性的提升，但也帶來發(fā)熱的增加。

西門子編碼器壞維修,西門子編碼器故障維修,西門子伺服電機維修,西門子伺服馬達維修,1FT5伺服電機維修,1FK6伺服馬達維修,1FT6電機維修,1FK7伺服電機維修,伺服電機1PH維修,西門子伺服電機離合器壞維修,西門子伺服電機剎車壞維修,西門子伺服電機軸承壞維修,西門子伺服電機電流高維修,西門子伺服電機電壓高維修、1FK7042-5AF71-1TH0維修

西門子伺服電機維修,西門子定制特制的非標電機,低壓電機維修,直流電機維修,西門子2KG電機維修,伺服電機維修,主軸電機維修,電機零部件(風扇,編碼器):

1PH系列維修 1FT5系列維修 1FT6系列維修 1FK6系列維修 1K7系列維修

ERN系列維修 EWN系列維修 ROD系列維修 2CW系列維修

1PA6105-4HF02-0BB3維修 1PA61054HF020BB3

1PA6133-4NF00-0BA3維修 1PA61334NF000BA3

1PA6163-4HF03-0BA3維修 1PA61634HF030BA3

1PA6163-4NF00-0BA3維修 1PA61634NF000BA3

1PH7101-2HF00-0BA3維修 1PH71012HF000BA3

1PH7101-2HF00-0BB3維修 1PH71012HF000BB3

1PH7101-2HF02-0BA3維修 1PH71012HF020BA3

1PH7101-2HF22-0BB3維修 1PH71012HF220BB3

1PH7101-2HF30-0BA0維修 1PH71012HF300BA0

1PH7101-2MF00-0BA3維修 1PH71012MF000BA3

1PH7101-2MF22-0BB3維修 1PH71012MF220BB3

1PH7101-2NF03-0BA0維修 1PH71012NF030BA0

1PH7103-2AD02-0BB3維修 1PH71032AD020BB3

1PH7103-2AD03-0BC3維修 1PH71032AD030BC3

1PH7103-2AF20-0BJ3維修 1PH71032AF200BJ3

1PH7103-2AG20-0BJ3維修 1PH71032AG200BJ3

1PH7103-2HD02-0BA0維修 1PH71032HD020BA0

1PH7103-2HD02-0BB3維修 1PH71032HD020BB3

1PH7103-2HD03-0BC3維修 1PH71032HD030BC3

1PH7103-2HF32-1KA3維修 1PH71032HF321KA3

1PH7103-2HG00-0BB3維修 1PH71032HG000BB3

1PH7103-2HG22-0BC3維修 1PH71032HG220BC3

1PH7103-2HG22-0BD3維修 1PH71032HG220BD3

1PH7103-2JF00-0BA3維修 1PH71032JF000BA3

1PH7103-2NF00-0BJ0維修 1PH71032NF000BJ0

1PH7103-2NF02-0BC0維修 1PH71032NF020BC0

1PH7103-2NF02-0BJ0維修 1PH71032NF020BJ0

1PH7103-2NF03-0BJ0維修 1PH71032NF030BJ0

1PH7103-2NF22-0BA0維修 1PH71032NF220BA0

1FE1051-6WN10-1BA0維修 1FE10516WN101BA0

1FE1052-6WN10-1BC2維修 1FE10526WN101BC2

1FE1082-4WN11-1BA2維修 1FE10824WN111BA2

1FE1092-6WN10-1BB0維修 1FE10926WN101BB0

1FE1092-6WN10-1BB2維修 1FE10926WN101BB2

1FE1116-6WR11-1BC2維修 1FE11166WR111BC2

1FK6032-6AK71-1SG0維修 1FK60326AK711SG0

1FK6032-6AK71-1SH0維修 1FK60326AK711SH0

1FK6032-6AK71-1TA2維修 1FK60326AK711TA2

1FK6032-6AK71-1TG0維修 1FK60326AK711TG0

1FK6040-6AK71-1AG0維修 1FK60406AK711AG0

1FK6040-6AK71-1AG2維修 1FK60406AK711AG2

1FK6040-6AK71-1AH0維修 1FK60406AK711AH0

1FK6040-6AK71-1TA0維修 1FK60406AK711TA0

1FK6042-6AF71-1AA2維修 1FK60426AF711AA2

1FK6042-6AF71-1AB0維修 1FK60426AF711AB0

1FK6042-6AF71-1AG0維修 1FK60426AF711AG0

1FK6042-6AF71-1AH0維修 1FK60426AF711AH0

1FK6042-6AF71-1EA0維修 1FK60426AF711EA0

1FK6042-6AF71-1EG0維修 1FK60426AF711EG0

1FK6042-6AF71-1EG2維修 1FK60426AF711EG2

1FK6042-6AF71-1EH0維修 1FK60426AF711EH0

1FK6042-6AF71-1GB2維修 1FK60426AF711GB2

1FK6042-6AF71-1GG0維修 1FK60426AF711GG0

1FK6042-6AF71-1GH2維修 1FK60426AF711GH2

1FK6042-6AF71-1SA0維修 1FK60426AF711SA0

1FK6042-6AF71-1SG0維修 1FK60426AF711SG0

1FK6042-6AF71-1SG2維修 1FK60426AF711SG2

1FK6042-6AF71-1SH0維修 1FK60426AF711SH0

1FK6042-6AF71-1TA0維修 1FK60426AF711TA0

1FK6042-6AF71-1TB0維修 1FK60426AF711TB0

1FK6042-6AF71-1TG0維修 1FK60426AF711TG0

1FK6042-6AF71-1TH0維修 1FK60426AF711TH0

1FK6060-6AF71-1AA2維修 1FK60606AF711AA2

1FK6060-6AF71-1AB0維修 1FK60606AF711AB0

1FK6060-6AF71-1AG0維修 1FK60606AF711AG0

1FK6060-6AF71-1AH0維修 1FK60606AF711AH0

1FK6060-6AF71-1EA0維修 1FK60606AF711EA0

1FK6060-6AF71-1EG0維修 1FK60606AF711EG0

1FK6060-6AF71-1EH0維修 1FK60606AF711EH0

1FK6060-6AF71-1TG0維修 1FK60606AF711TG0

1FK6063-6AF71-1AA2維修 1FK60636AF711AA2

1FK6063-6AF71-1AB0維修 1FK60636AF711AB0

1FK6063-6AF71-1AB2維修 1FK60636AF711AB2

1FK6063-6AF71-1AG0維修 1FK60636AF711AG0

1FK6063-6AF71-1AG2維修 1FK60636AF711AG2

1FK6063-6AF71-1AH0維修 1FK60636AF711AH0

1FK6063-6AF71-1AH2維修 1FK60636AF711AH2

1FK6063-6AF71-1EG0維修 1FK60636AF711EG0

1FK6063-6AF71-1EH0維修 1FK60636AF711EH0

1FK6063-6AF71-1GH2維修 1FK60636AF711GH2

1FK6063-6AF71-1SA0維修 1FK60636AF711SA0

1FK6063-6AF71-1TB0維修 1FK60636AF711TB0

1FK6063-6AF71-1TG0維修 1FK60636AF711TG0

1FK6063-6AF71-1TH0維修 1FK60636AF711TH0

1FK6080-6AF71-1AG0維修 1FK60806AF711AG0

1FK6080-6AF71-1TH0維修 1FK60806AF711TH0

1FK6083-6AF71-1AB0維修 1FK60836AF711AB0

1FK6083-6AF71-1AG0維修 1FK60836AF711AG0

1FK6083-6AF71-1AG2維修 1FK60836AF711AG2

1FK6083-6AF71-1AH0維修 1FK60836AF711AH0

1FK6083-6AF71-1EA0維修 1FK60836AF711EA0

1FK6083-6AF71-1EB0維修 1FK60836AF711EB0

1FK6083-6AF71-1EG0維修 1FK60836AF711EG0

1FK6083-6AF71-1EH0維修 1FK60836AF711EH0

1FK6083-6AF71-1TB0維修 1FK60836AF711TB0

1FK6083-6AF71-1TH0維修 1FK60836AF711TH0

1FK6100-8AF71-1AH0維修 1FK61008AF711AH0

1FK6100-8AF71-1SA0維修 1FK61008AF711SA0

1FK6100-8AF71-1TA0維修 1FK61008AF711TA0

1FK6101-8AF71-1AA0維修 1FK61018AF711AA0

1FK6101-8AF71-1AG0維修 1FK61018AF711AG0

1FK6103-8AF71-1AB2維修 1FK61038AF711AB2

1FK6103-8AF71-1AH0維修 1FK61038AF711AH0

1FK6103-8AF71-1EH2維修 1FK61038AF711EH2

1FK7015-5AK71-1AB0維修 1FK70155AK711AB0

1FK7022-5AK21-1DA0維修 1FK70225AK211DA0

1FK7022-5AK21-1DA3維修 1FK70225AK211DA3

1FK7022-5AK21-1DB0維修 1FK70225AK211DB0

1FK7022-5AK21-1DB3維修 1FK70225AK211DB3

1FK7022-5AK21-1DG0維修 1FK70225AK211DG0

1FK7022-5AK21-1DG3維修 1FK70225AK211DG3

1FK7022-5AK21-1DH0維修 1FK70225AK211DH0

1FK7022-5AK21-1DH3維修 1FK70225AK211DH3

1FK7022-5AK21-1LA0維修 1FK70225AK211LA0

1FK7022-5AK21-1LA3維修 1FK70225AK211LA3

1FK7022-5AK21-1LB0維修 1FK70225AK211LB0

1FK7022-5AK21-1LG0維修 1FK70225AK211LG0

1FK7022-5AK21-1LG3維修 1FK70225AK211LG3

1FK7022-5AK21-1LH0維修 1FK70225AK211LH0

1FK7022-5AK21-1LH3維修 1FK70225AK211LH3

1FK7022-5AK21-1PA0維修 1FK70225AK211PA0

1FK7022-5AK21-1PA3維修 1FK70225AK211PA3

1FK7022-5AK21-1PB0維修 1FK70225AK211PB0

1FK7022-5AK21-1PB3維修 1FK70225AK211PB3

1FK7022-5AK21-1PG0維修 1FK70225AK211PG0

1FK7022-5AK21-1PG3維修 1FK70225AK211PG3

1FK7022-5AK21-1PH0維修 1FK70225AK211PH0

1FK7022-5AK21-1PH3維修 1FK70225AK211PH3

1FK7022-5AK21-1SA0維修 1FK70225AK211SA0

1FK7022-5AK21-1SA3維修 1FK70225AK211SA3

1FK7022-5AK21-1SB0維修 1FK70225AK211SB0

1FK7022-5AK21-1SB3維修 1FK70225AK211SB3

1FK7022-5AK21-1SG0維修 1FK70225AK211SG0

1FK7022-5AK21-1SG3維修 1FK70225AK211SG3

1FK7022-5AK21-1SH0維修 1FK70225AK211SH0

1FK7022-5AK21-1SH3維修 1FK70225AK211SH3

1FK7022-5AK21-1TA0維修 1FK70225AK211TA0

1FK7022-5AK21-1TA3維修 1FK70225AK211TA3

1FK7022-5AK21-1TB0維修 1FK70225AK211TB0

1FK7022-5AK21-1TB3維修 1FK70225AK211TB3

1FK7022-5AK21-1TG0維修 1FK70225AK211TG0

1FK7022-5AK21-1TG3維修 1FK70225AK211TG3

1FK7022-5AK21-1TH0維修 1FK70225AK211TH0

1FK7022-5AK21-1TH3維修 1FK70225AK211TH3

1FK7022-5AK21-1UA0維修 1FK70225AK211UA0

1FK7022-5AK21-1UA3維修 1FK70225AK211UA3

1FK7022-5AK21-1UB0維修 1FK70225AK211UB0

1FK7022-5AK21-1UB3維修 1FK70225AK211UB3

1FK7022-5AK21-1UG0維修 1FK70225AK211UG0

1FK7022-5AK21-1UG3維修 1FK70225AK211UG3

1FK7022-5AK21-1UH0維修 1FK70225AK211UH0

1FK7022-5AK21-1UH3維修 1FK70225AK211UH3

1FK7022-5AK71-1AA0維修 1FK70225AK711AA0

1FK7022-5AK71-1AA5維修 1FK70225AK711AA5

1FK7022-5AK71-1AB0維修 1FK70225AK711AB0

1FK7022-5AK71-1AG2維修 1FK70225AK711AG2

1FK7022-5AK71-1DA0維修 1FK70225AK711DA0

1FK7022-5AK71-1DG0維修 1FK70225AK711DG0

1FK7022-5AK71-1HG0維修 1FK70225AK711HG0

1FK7022-5AK71-1HH0維修 1FK70225AK711HH0

1FK7022-5AK71-1HH3維修 1FK70225AK711HH3

1FK7022-5AK71-1LA3維修 1FK70225AK711LA3

1FK7022-5AK71-1LG0維修 1FK70225AK711LG0

1FK7022-5AK71-1LG3維修 1FK70225AK711LG3

1FK7022-5AK71-1PA0維修 1FK70225AK711PA0

1FK7022-5AK71-1PA3維修 1FK70225AK711PA3

1FK7022-5AK71-1PG3維修 1FK70225AK711PG3

1FK7022-5AK71-1SG0維修 1FK70225AK711SG0

1FK7022-5AK71-1SG3維修 1FK70225AK711SG3

1FK7022-5AK71-1TA0維修 1FK70225AK711TA0

1FK7022-5AK71-1TG0維修 1FK70225AK711TG0

1FK7022-5AK71-1TH0維修 1FK70225AK711TH0

1FK7032-5AK71-1AB0維修 1FK70325AK711AB0

1FK7032-5AK71-1AG0維修 1FK70325AK711AG0

1FK7032-5AK71-1AG2維修 1FK70325AK711AG2

1FK7032-5AK71-1AG3維修 1FK70325AK711AG3

1FK7032-5AK71-1AH0維修 1FK70325AK711AH0

1FK7032-5AK71-1DA0維修 1FK70325AK711DA0

1FK7032-5AK71-1DA5維修 1FK70325AK711DA5

1FK7032-5AK71-1DG3維修 1FK70325AK711DG3

1FK7032-5AK71-1HA2維修 1FK70325AK711HA2

1FK7032-5AK71-1HG0維修 1FK70325AK711HG0

1FK7032-5AK71-1HH0維修 1FK70325AK711HH0

1FK7032-5AK71-1LG3維修 1FK70325AK711LG3

1FK7032-5AK71-1LH3維修 1FK70325AK711LH3

1FK7032-5AK71-1PA0維修 1FK70325AK711PA0

1FK7032-5AK71-1PA3維修 1FK70325AK711PA3

1FK7032-5AK71-1PG0維修 1FK70325AK711PG0

1FK7032-5AK71-1PG3維修 1FK70325AK711PG3

1FK7032-5AK71-1SA0維修 1FK70325AK711SA0

1FK7032-5AK71-1SG0維修 1FK70325AK711SG0

1FK7032-5AK71-1SH0維修 1FK70325AK711SH0

1FK7032-5AK71-1TA0維修 1FK70325AK711TA0

1FK7032-5AK71-1TG0維修 1FK70325AK711TG0

1FK7032-5AK71-1TG2維修 1FK70325AK711TG2

1FK7032-5AK71-1TH0維修 1FK70325AK711TH0

1FK7033-7AF21-1PA3維修 1FK70337AF211PA3

1FK7033-7AF21-1PB3維修 1FK70337AF211PB3

1FK7033-7AF21-1PG0維修 1FK70337AF211PG0

1FK7033-7AF21-1PG3維修 1FK70337AF211PG3

1FK7033-7AK71-1AA0維修 1FK70337AK711AA0

1FK7033-7AK71-1HG0維修 1FK70337AK711HG0

1FK7033-7AK71-1HH3維修 1FK70337AK711HH3

1FK7033-7AK71-1PG3維修 1FK70337AK711PG3

1FK7033-7AK71-1TA0維修 1FK70337AK711TA0

1FK7033-7AK71-1TG0維修 1FK70337AK711TG0

1FK7033-7AK71-1TH0維修 1FK70337AK711TH0

1FK7034-5AK71-1AG3維修 1FK70345AK711AG3

1FK7034-5AK71-1AH0維修 1FK70345AK711AH0

1FK7034-5AK71-1DG0維修 1FK70345AK711DG0

1FK7034-5AK71-1PA0維修 1FK70345AK711PA0

1FK7034-5AK71-1PG0維修 1FK70345AK711PG0

1FK7034-5AK71-1TH0維修 1FK70345AK711TH0

1FK7040-5AK71-1AG0維修 1FK70405AK711AG0

1FK7040-5AK71-1AG8維修 1FK70405AK711AG8

1FK7040-5AK71-1DA5維修 1FK70405AK711DA5

1FK7040-5AK71-1DB2維修 1FK70405AK711DB2

1FK7040-5AK71-1EA0維修 1FK70405AK711EA0

1FK7040-5AK71-1EG0維修 1FK70405AK711EG0

1FK7040-5AK71-1EH0維修 1FK70405AK711EH0

1FK7040-5AK71-1SA2維修 1FK70405AK711SA2

1FK7040-5AK71-1SH0維修 1FK70405AK711SH0

1FK7040-5AK71-1TA0維修 1FK70405AK711TA0

1FK7040-5AK71-1TA2維修 1FK70405AK711TA2

1FK7040-5AK71-1TA3維修 1FK70405AK711TA3

1FK7040-5AK71-1TG0維修 1FK70405AK711TG0

1FK7040-5AK71-1TH2維修 1FK70405AK711TH2

1FK7042-5AF21-1PA3維修 1FK70425AF211PA3

1FK7042-5AF21-1PB3維修 1FK70425AF211PB3

1FK7042-5AF21-1PG3維修 1FK70425AF211PG3

1FK7042-5AF21-1SG3維修 1FK70425AF211SG3

1FK7042-5AF71-1AA0維修 1FK70425AF711AA0

1FK7042-5AF71-1AA2維修 1FK70425AF711AA2

1FK7042-5AF71-1AB0維修 1FK70425AF711AB0

1FK7042-5AF71-1AG0維修 1FK70425AF711AG0

1FK7042-5AF71-1AG2維修 1FK70425AF711AG2

1FK7042-5AF71-1AG5維修 1FK70425AF711AG5

1FK7042-5AF71-1AH0維修 1FK70425AF711AH0

1FK7042-5AF71-1AH2維修 1FK70425AF711AH2

1FK7042-5AF71-1DG3維修 1FK70425AF711DG3

1FK7042-5AF71-1EA0維修 1FK70425AF711EA0

1FK7042-5AF71-1EA2維修 1FK70425AF711EA2

1FK7042-5AF71-1EA3維修 1FK70425AF711EA3

1FK7042-5AF71-1EA5維修 1FK70425AF711EA5

1FK7042-5AF71-1EB2維修 1FK70425AF711EB2

1FK7042-5AF71-1EG0維修 1FK70425AF711EG0

1FK7042-5AF71-1EG2維修 1FK70425AF711EG2

1FK7042-5AF71-1EG3維修 1FK70425AF711EG3

1FK7042-5AF71-1EH0維修 1FK70425AF711EH0

1FK7042-5AF71-1EH2維修 1FK70425AF711EH2

1FK7042-5AF71-1FA5維修 1FK70425AF711FA5

1FK7042-5AF71-1FB0維修 1FK70425AF711FB0

1FK7042-5AF71-1FG5維修 1FK70425AF711FG5

1FK7042-5AF71-1FH3維修 1FK70425AF711FH3

1FK7042-5AF71-1GA5維修 1FK70425AF711GA5

1FK7042-5AF71-1GB0維修 1FK70425AF711GB0

1FK7042-5AF71-1GB2維修 1FK70425AF711GB2

1FK7042-5AF71-1GG0維修 1FK70425AF711GG0

1FK7042-5AF71-1GG3維修 1FK70425AF711GG3

1FK7042-5AF71-1GH2維修 1FK70425AF711GH2

1FK7042-5AF71-1GH5維修 1FK70425AF711GH5

1FK7042-5AF71-1KA3維修 1FK70425AF711KA3

1FK7042-5AF71-1KA5維修 1FK70425AF711KA5

1FK7042-5AF71-1KB0維修 1FK70425AF711KB0

1FK7042-5AF71-1KG0維修 1FK70425AF711KG0

1FK7042-5AF71-1KG3維修 1FK70425AF711KG3

1FK7042-5AF71-1PA0維修 1FK70425AF711PA0

1FK7042-5AF71-1PA3維修 1FK70425AF711PA3

1FK7042-5AF71-1PB3維修 1FK70425AF711PB3

1FK7042-5AF71-1PG0維修 1FK70425AF711PG0

1FK7042-5AF71-1PG3維修 1FK70425AF711PG3

1FK7042-5AF71-1TG2維修 1FK70425AF711TG2

1FK70425AF711TH0

1FK7042-5AF71-1TH2維修 1FK70425AF711TH2

1FK7042-5AF71-1UA0維修 1FK70425AF711UA0

1FK7042-5AF71-1UA3維修 1FK70425AF711UA3

1FK7042-5AF71-1UB0維修 1FK70425AF711UB0

1FK7042-5AF71-1UG0維修 1FK70425AF711UG0

1FK7042-5AK71-1AB2維修 1FK70425AK711AB2

1FK7042-5AK71-1AB5維修 1FK70425AK711AB5

1FK7042-5AK71-1AH5維修 1FK70425AK711AH5

1FK7042-5AK71-1EB5維修 1FK70425AK711EB5

1FK7042-5AK71-1EG0維修 1FK70425AK711EG0

1FK7042-5AK71-1EH0維修 1FK70425AK711EH0

1FK7042-5AK71-1EH2維修 1FK70425AK711EH2

1FK7042-5AK71-1EH5維修 1FK70425AK711EH5

1FK7042-5AK71-1FA0維修 1FK70425AK711FA0

1FK7042-5AK71-1FG0維修 1FK70425AK711FG0

1FK7042-5AK71-1FH0維修 1FK70425AK711FH0

1FK7042-5AK71-1GB2維修 1FK70425AK711GB2

1FK7042-5AK71-1KB0維修 1FK70425AK711KB0

1FK7042-5AK71-1PA0維修 1FK70425AK711PA0

1FK7042-5AK71-1PG3維修 1FK70425AK711PG3

1FK7042-5AK71-1SA0維修 1FK70425AK711SA0

1FK7042-5AK71-1TA0維修 1FK70425AK711TA0

1FK7042-5AK71-1TA2維修 1FK70425AK711TA2

1FK7042-5AK71-1TA3維修 1FK70425AK711TA3

1FK7042-5AK71-1TG0維修 1FK70425AK711TG0

1FK7042-5AK71-1TG2維修 1FK70425AK711TG2

1FK7043-7AF21-1PA0維修 1FK70437AF211PA0

1FK7043-7AF21-1PG3維修 1FK70437AF211PG3

1FK7043-7AF21-1PH3維修 1FK70437AF211PH3