PLC的工作方式为扫描加中断，这既可保证它能有序地工作，避免继电控制系统常出现的"冒险竞争"，其控制结果总是确定的；而且又能应急处理急于处理的控制，保证了PLC对应急情况的及时响应，使PLC能可靠地工作。

为监控PLC运行程序是否正常，PLC系统都设置了"看门狗"（Watchingdog）监控程序。运行用户程序开始时，先清"看门狗"定时器，并开始计时。当用户程序一个循环运行完了，则查看定时器的计时值。若超时（一般不超过100ms），则报警。严重超时，还可使PLC停止工作。用户可依报警信号采取相应的应急措施。定时器的计时值若不超时，则重复起始的过程，PLC将正常工作。显然，有了这个"看门狗"监控程序，可保证PLC用户程序的正常运行，可避免出现"死循环"而影响其工作的可靠性。

PLC还有很多防止及检测故障的指令，以产生各重要模块工作正常与否的提示信号。可通过编制相应的用户程序，对PLC的工作状况，以及PLC所控制的系统进行监控，以确保其可靠工作。

PLC每次上电后，还都要运行自检程序及对系统进行初始化。这是系统程序配置了的，用户可不干预。出现故障时有相应的出错信号提示。

正是PLC在软、硬件诸方面有强有力的可靠性措施，才确保了PLC具有可靠工作的特点。它的平均无故障时间可达几万小时以上；出了故障平均修复时间也很短，几小时以至于几分钟即可。

ACE CONTROLS SHOCK ABSORBER MC600 PSI

ARO PNEUMATIC AIR POWERED ELECTRODE DRESSER TOOL MODEL 8040

NUMATICS F30B-04AC / C30D-04ACG PNEUMATIC FILTERS NNB

BIMBA FOD-501 PNEUMATIC CYLINDER NNB

UNKNOWN MANUFACTURER * BUTTON HEAD GREASE FITTING * UNKNOWN

NUMATICS R22R-04G REGULATOR, NNB

NUMATICS 120V, 50/60Hz, 150PSIG, SOLENOID VALVE 081SS400K000030

UNKNOWN MANUFACTURER * SS HEX HEAD BUSHING ASSORTED * UNKNOWN

PARKER 250PSI BORE-3.25 STR-12.000 PNEUMATIC CYLINDER CJAUS13C

MAC 110/120V 26.8W 50/60HZ 150 PSI PNEUMATIC SOLENOID VALVE COIL, PID-111CAAA

PARKER * PNEUMATIC CYLINDER * 32CBCMPRS14MC

BIMBA PNEUMATIC CYLINDER 174-DP

NUMATICS AIR CYLINDER 08-28733

MAGNATROL 120V 60Hz SOLENOID VALVE 14L32-ZM

YUKEN HYDRAULIC CYLINDER CJT70-FA32B370B?-BDA 11 A

NUMATICS 150 PSIG SOLENOID VALVE 122BB572MN00061

FESTO CPV14-VI N702 DISTRIBUTION MANIFOLD NO CONNECTOR PLATE

FESTO 40mm BORE 400mm STROKE PNEUMATIC CYLINDER DNG-40-400-PPV-?A

PHD SKC74 X 205 -DB-PB CYLINDER 06634821-02 NNB

DRAIN-ALL SERIAL 40420 COMPRESSED PNEUMATIC AIR DRAIN TRAP LIQUID VALVE 1500

FESTO 180 PSI 100MM BORE 100MM STROKE PNEUMATIC CYLINDER, DNG-100-100-PPV?-A, NNB

TRABON / LUBRIQUIP 0.015IN3 (0.246CM3) MODULAR DIVIDER VALVE MSP-15T

FESTO 50MM BORE 100MM STROKE PNEUMATIC CYLINDER, DNC-50-100-PPV-?A, NNB

FESTO 40MM BORE 125MM STROKE PNEUMATIC CYLINDER, DNU-40-125PPV-A?, NNB

BELLOWS-VALVAIR LTD AIR CYLINDER B0511 0041 70

PNEUTRONICS DIGITAL PNEUMATIC CONTROL BOARD 990-004765-011

NUMATICS 120V .12A 150 PSIG-AIR SOLENOID VALVE W/ BASE, 082SA43AK

NUMATICS 150 PSIG-MAX SOLENOID VALVE ISO5599/11 / I34BB400KP14D

ZIMMER PNEUMATIC CLAMPING ELEMENT MKS3501A NIB

NUMATICS 24VDC 6.0W PNEUMATIC SOLENOID VALVE 225-372B

YUKEN HYDRAULIC CYLINDER CJT70-FA32B31B-?ABA-EK

SMC CYLINDER CDNAFN63N-220-D

PARKER SCHRADER BELLOWS 150PSI SOLENOID COIL NNB AL41533BJN5300B 103644

AEROQUIP A-T-J DIVISION HYDRAULIC CYLINDER TE22CAXD

ROTAC ROTARY ACTUATOR DUEL SHAFT LP-24-IV

NUMATICS LINEAR SLIDE LC10602H16DXX

BOSCH PNEUMATIC STOP GATE 3842 525 109 *NNB*

SMC JAF140-30-150 FLOATING JOINT, NIB

SMC PNEUMATIC CYLINDER CNDAFN80N-125-D

PARKER K065 N035 PILOT VALVE, NNB

NUMATICS .916" NPT FILTER F30B-06

SMC CYLINDER CLAFN80-75-D-XC?18

SMC PNEUMATIC CYLINDER MYH32-K5232-400

FESTO 63MM BORE 300MM STROKE PNEUMATIC CYLINDER, DNC-63-300-PPV-?A-KP, NNB

ASCO 24DC-FT 11.2W SOLENOID N262.444 E / 400-425-142

NUMATICS 100-120V .30A 150 PSIG-AIR SOLENOID VALVE, I35SA415K

PARKER HYDRAULIC FILTER 926988Q NIB

EATON AEROQUIP FJ9122-1212 37JIC FEMALE SWIVEL ,NNB

BIMBA PNEUMATIC CYLINDER 245-DP

DEZURIK CYLINDER ACTUATOR 941816R001 44482

HOWA ROTATING HYDRAULIC CHUCK CYLINDER HH11C 80

PMV 800kPA ELECTRO-PNEUMAT?IC DOUBLE ACTING VALVE POSITIONER P-2020 NIB

WHITEY 200PSI MAX 90 PNEUMATIC SPRING RETURN ACTUATOR 133 SR W/ MB-133

CMT 80 PSI, 2.5" STROKE DOUBLE ACTING IMPACT MARKER 288SUBK.OB.25.R

YUKEN CYLINDER CJT70-TC40B320B?-ABA-EK 20A

PARKER SCHRADER BELLOWS 24 VDC SOLENOID PNEUMATIC VALVE W2154L579B

YUKEN HYDRAULIC CYLINDER CJT70-FA32B325B?-BCB-EK 20A

FESTO PNEUMATIC CYLINDER DZH-50-200PPV-A

NUMATICS 120V, .16A, 50/60Hz, SOLENOID VALVE 554BB43AK

PHD PNEUMATIC PARALLEL GRIPPER 7980-03-0201

FESTO CYLINDER DKE-100-350-PPV?-A

NUMATICS 24VDC 4.0W 150 PSIG-AIR PNEUMATIC SOLENOID VALVE, I24BB415MP56Y

NUMATICS 110/120V .06A 150 PSIG-AIR DOUBLE SOLENOID VALVE, I34BB400KP14D

MAC 24VDC 2.5W 25-150 PSI PNEUMATIC SOLENOID VALVE, 6313D-611-PM-59?1DA

PARKER PNEUMATIC 150PSI 1000KPA FILTER/REGULATO?R 07F41BC 104112

ENERPAC STLS-121 2400LB THREADED BODY SWING CYLINDER, NNB

CKD SSD-ML-40-40 PNEUMATIC CYLINDER

PARKER E-43-B-0500 INSTRUMENT GRADE POLYETHYLENE TUBING .170" X 500', NIB

NUMATICS 110/120V .08A SOLENOID VALVE, 237-325B

SMC CYLINDER CDLAFN100-175-E

BIMBA SS PNEUMATIC CYLINDER SS311-R

PARKER * SAE CODE 61 FLANGE HEAD * 11571-16-16

NUMATICS SOLENOID AIR PILOT ACTUATED VALVE R20BB500MP00061 / R20BBD00MP00061

SMC 3.5MPa PNEUMATIC CYLINDER CHDAL40-400-J59?WL

INTEGRAL HYDRAULIK HYDRAULIC CYLINDER1009882?1 160BAR 018-1354-062-00?3

NUMATICS 238610 110/120V 50/60HZ SOLENOID VALVE COIL, MP-C-080-032-D

MILCO PNEUMATIC CYLINDER CCC-204-4.0 REV B 100712

90 BRASS ELBOW ASSORTMENT, LOT OF 9

NUMATICS SERIES ISO5599/11 150 PSIG SOLENOID VALVE I24BB415MP

PARKER JIC P 16 SS FLUID CONNECTING NUT, LOT OF 17

HYDRAULIC THREAD NUT HMV 134/A-101