Safety points regarding implementation of overall inspection
Cut off the current
Stick stickers prohibiting throwing the switch
Have an accurate knowledge of the nature of electricity and know how to handle it correctly
Electricity at fist sounds scary. However, when the nature of electricity and how to handle is well known, electricity ceases to be scary.
However, one cannot afford to be careless about electricity. When performing general inspection of electric control system, a basic condition is that the inspection be witnessed by a person specially trained in low-tension electricity
Overall inspections of electric control systems must be performed on the secondary side.
Overall inspections of electric systems vary according to the equipment, but generally one draws a flowehart based on the equipment specifications and drawings to establish the locations to be inspected. The locations that are to be inspected by operators are usually the secondary electric system as shown in the figure below.
Dirt, dust, water, rust, etc…, which impede the passage of current, must be thoroughtly cleaned away and their eniry must be prevented.
Electricity is the nervous system that gives equipment instructions to move. It takes a lot of time to find malfunctions of the nevous system, and many problems on safety arise.
What is the target to inspect?
What is proper condition or ideal condition as it should be?
IS proper condition or ideal condition maintained?
Air their function and construction understood?
Are inspection method and judgment of abnormal understood?
Is ameasure understood?
Overall inspection of main switch of equipment
Defect in main switch
Cause leakage, lower the conductivity, and lower safety and quality
Overal inspection of control panel
Defects in control panel
Cause variation and non-uniformity in control function, quality defects, and invite failures and stoppages
Also invite leakage and lower safety
Overall inspection of operation panel
Defect in operation panel
Cause variation and non-uniformity in control function, quality defects, and invite failures and stoppages
Also invite leakage and lower safety
Overall inspection of external wiring
Defects in external wiring
Cause worsened insulation resistnce and shorts, also cause leakage incidents and equipment failures.
Overall inspection of relay box
Defect in relay box
Cause defective contact, invite sparks and heating, poor conduction, and malfunctions, as well as quality defects.
Also cause failures and stoppages due to noise
Overall inspection of motor
Defects in electric motor
Cause worsened insulation resistance and conduction, irregular operator of electric motor, and invite quality defects.
Cause leakage, lower safety, and failure and stoppage
Overall inspect of sensor
Defect in sensor
Prevent accurate measurements, cause quality defects and failures and stoppage due to maifunctions, and worsen safety.
Electricity flows like water. This flow is called current
The strength with which current flows is called voltage.
The voltage used in plants is usually 200v, and is used for such things as equipment, are welders, and obtained from general purpose electric outlets.
DC và AC
Voltage and current are divided into direct current and alternative current
Direct current flows only in one direction, and is abbrevisted as the symbol DC. Alternative current changes in the direction and intensity of its flow at fixed cycles. This type of current is abbreviated as the symbol AC. The number of cycles per second is expressed in Hz. ( Plants receive their electricity as 50 Hz or 60 Hz. Within equipment, direct current of 12 V or 24 V is used)
Insulation resistance
When voltage is applied to an insulator, an infinitesimal current passes, as the resistance is not unlimited, The parameter measuring insulation performance is called insulation resistance. The higher this valure, the better the performance of the insulator.
The unit used to represent insulation resistance is the ohm and megohm, which is 1 millin ohms. ( Generally, the insulation resistance passes, as the resistance of electric tools should be 01M
Or higher in 100 V circuits, and 2 M or higher in 200 V circuits
Risk of electrocution
The risk of electrocution exists regardless of the voltage level, and is determined by the following.
Current value
The human body can feel 1 mA
Voltage levels m or 15 mA or more required care.
Voltage levels of 250 mA or more present a danger to life
Electrocution length
Naturally, the longer the electrocution, the greater the danger, Even 100 V cause a danger to life even for o period of only 1 sec.
Types of power supplies
DC current of 60 Hz is about 4 to 5 times more dangerous than direct current
Electric circuits
Generally, an electric short k with 100 V at 2mA will cause a slight pricking sensation. However, this becomes 20 mA if one is sweating, and 50 mA if the current leaks in water, which is extremely dangerous.
Handling electricity and safety points
Electricity is a useful form of energy that also contains an element of danger. As a result, various efforts are made to ensure safety with regard to equipment, such as keeping wires from touching one another and insulating or molding charged parts so that they cannot be touched dicrectly, yet it is not possible to completely mold all charged parts. Furthermore, insulators are prone to degradation, and thus persons handling electricity should take the folloeing handling precautions.
Do not touch electric equipment with wet hands ( especially switches)
Use gloves
Do not touch bare parts
Prior to inspecting electric equipment, be sure to turn off electric switches, and make sure that parts are not changed ( using electroscope)
Turn on switches from the power source side, and turn off switches from the load side.
Do not touch cut wires that hang down
Do not splash water on electric equipment, not place dirt on such equipment, do not obstruct grounding, and do not apply heat.
Electroscopes serve to detect the presence of voltage using discharge of a neon tube, and come in various types, such as low voltage, high voltage, and very high voltage.
Low voltage electroscopes are of two types, driver type and pecil tupe, Electroscopee from a circuit through the passage of current from the electric discharge tube into the human body. When using them, one must be sure to wear a grounding electrode clip. Exposing the electroscope to water in cuch a case is dangerous.
Electroscopes phục vụ để phát hiện sự hiện diện của điện áp sử dụng xả ống neon, và có nhiều kiểu khác nhau, chẳng hạn như điện áp thấp, điện áp cao và điện áp rất cao.
Electroscopes điện áp thấp có hai loại, loại xe và loại pecil, Electroscopes từ một mạch qua đoạn hiện nay từ các ống phóng điện vào cơ thể con người. Khi sử dụng chúng, người ta phải chắc chắn để mặc một clip nền tảng điện cực. Phơi bày cái điện nước trong trường hợp như vậy là nguy hiểm.
Important Guidelines
Cut off the current, Stick stickers prohibiting throwing the switch
Clearly indicale to all what equipment will be inspected that day.
Fully understand primary and secondary sides.
Know how to use an electroscope.
Is maintenance power supply taken from primory side?
Are the clothes worn adequate? ( bare skin not exposed)
Is the use of testers known?
Inexperienced persons must work in learns ( with experienced person)
Are hands wet with water or oil?
Use specified electric tools.
Inspection of tools at start of inspection ( how many types are used)
Inspection of tools a end of inspection ( Check all tools are there)
At end of inspection, switch on current
Limit switch consist of a case made of metal or resin that protects micro switches from environmental factors such as external force, water, oil, dust, eye, Moreover, they include an actuator mechanism for detecting mechanical motion.
Head in the case of limit switches, have an independent mechanism as actuator mechanism.
Actuator applied external force is transmitted to an internal spring mechanism and moves a traveling contact causing closing or opening of the switch.
Contact detection switches
Micro switch ( position, displacement)
Doll micro switch (position, displacement)
…
Non-contact switch
Photo switch ( position, displacement)
...
Points regarding installation
The surrounding environment is an important factor to consider to ensure the proper operation of limit switches. The table below list failures of limit switches.
Based on this, the following considerations are required when installing limit switches.
Penetration of water or oil
Defective contacts, grounding, short circuit
Change installation location. Provide a cover
Machine insufficiently strong
Excessive speed of actuated object
Brocken lever or spring, loose mounting
Correct cutting of limit seat, survey of physical charateristics of actuated object
Unfavorable installation lacation
Failures srising because inspections are not possible
Change installation location
Excessive ambient temperature
Deteriorated wiring, corrodert contact
Change installation location. Install double cover and cooling
Accumilation of dust
Operation defects in actuator, defective contact, short circuits
Change installation location. Implement dustproof measure.
Operation by human operators
Manfunction
Install manfunction prevention fence
Defective wiring
Brocken wires
Don’t apply strees to wires
Points Regarding Installation of limit switches
Design of dog
To ensure the proper operation of limit switches and prevent the breakage of actuators, it is important to select the proper speed and angle for the dog. Generally, an operation speed of 0.5 m/s or lower, and an angle of 30 to 45 are considered to be adepuate.
Electric Safety Guiderlines Checklist
Overall inspections of electric systems should be performed only after low voltage electricity technicians has verified the safety of the entire facilitiesnand t
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