6.3 Clamp Ammeter
1.Basic Structure and Function of Tong-type Ammeter
(1)Basic structure
Tong-type ammeter,is mainly composed of an electromagnetic ammeter and a throughtype current transformer.The core of the through-type current transformer is made into a movable opening and is tong-shaped,hence it is named as tong-type ammeter.Fig.6-18 shows the structure diagram of tong-type ammeter.
Fig.6-18 Structure Diagram of Tong-type Ammeter
1-Bayonet;2-Data lock button;3-Gear selection;4-Digital display screen;5-Terminal block;6-Wrench
(2)Basic function
Tong-type ammeter is a kind of portable instrument that can directly measures AC current of circuit without disconnecting the circuit,which is very convenient to use in electrical maintenance.
2.Classification and Technical Specifications of Tong-type Ammeter
(1)Classification
①Classified as pointer type and digital type according to the display mode.
②Classified as AC clamp ammeter,multi-purpose clamp ammeter,harmonic digital clamp ammeter,leakage clamp ammeter and AC-DC clamp ammeter according to the function.
③Classified as high-voltage clamp meter and low-voltage clamp meter according to the measured voltage.
④Classified as transformer type and electromagnetic system type according to the structure and application.Commonly used is transformer type tong-type ammeter,which consists of current transformer and rectifier instrument It can only measure alternating current.The deflection of the movable part of the electromagnetic instrument is unrelated to the polarity of current,so it can be used in both AC and DC.
(2)Technical specifications
The accuracy of tong-type ammeter mainly includes 2.5,3.0 and 5.0 grades.
3.Check Contents of Tong-type Ammeter
The tong-type ammeter must be inspected before use as follows.
(1)Check whether the tong-type ammeter has the factory certificate and calibration certificate,and whether it is within the validity period of the test.
(2)Before use,check whether the tong-type ammeter is damaged and whether the pointer points to zero.If it is found that the pointer does not point to the zero position,use a small screwdriver to gently turn the mechanical zero adjustment knob to return the pointer to the zero position.
(3)Check whether the insulation material on the jaw has any damage such as falling off and cracking,and whether there is any obvious gap after closing.If so,it must be repaired before use.
(4)Check the whole shell of tong-type ammeter,including gauge glass,which shall be free of cracking and breakage,because the insulation of the jaw and the integrity of the meter shell are directly related to the safety of measurement and the performance of the meter.
(5)For multi-purpose tong-type ammeter,check whether the test line and meter bar are damaged,and they shall have good conductivity and be free of damage.
(6)For the digital tong-type ammeter,it is also necessary to check whether the battery in the checklist is sufficient or not,and it must be updated if insufficient.
Fig.6-19 shows the inspection of tong-type ammeter.(https://www.daowen.com)
Fig.6-19 Inspection of Tong-type Ammeter
4.Usage of Tong-type Ammeter
(1)Before measurement,the current to be measured shall be estimated first to select appropriate range.If it is not possible to estimate,a large range shall be selected first,and then reduced gradually to the appropriate gear.The shifting of range gear must be done in the case of no electricity or under the opening of the jaw so as not to damage the instrument.
(2)During measurement,the measured conductor shall be placed in the middle of the jaw as far as possible.If there is noise on the joint surface of the jaw,it shall be opened and closed again.If there is still noise,the joint surface shall be treated to make the reading accurate.In addition,the two conductors cannot be clamped at the same time.
(3)The measurement of high-voltage clamp ammeter shall be operated by two persons wearing insulating gloves and standing on insulating pad without touching other equipment to prevent short circuit or grounding.
(4)When measuring the current below 5A,in order to get a more accurate reading,if possible,the conductor should be wound several times before put into the jaw for measurement.The actual current value shall be the instrument reading divided by the number of conductors put into the jaw.
(5)During the measurement,a safe distance shall be kept between all parts of the body and the electrified body.The safety distance of the low-voltage system is 0.1-0.3m.When measuring current of each phase of high-voltage cable,the distance between the cable head and conductor shall be more than 300mm,with good insulation and measuring operation conditions.When observing the meter,a safe distance between the head and the electrified part shall be kept.The distance between any part of the human body and the electrified body shall not be less than the entire length of the clamp meter.
(6)When measuring low-voltage fusible fuse or horizontal arranged low-voltage bus current,each phase fuse and busbar shall be protected and isolated by insulating materials,so as not to cause inter-phase short-circuit.If one phase of cable is grounded,measurement is not allowed,so as to prevent breakdown of the ground due to the low insulation level of the cable head,which shall endanger personal safety.
(7)Before and after each measurement,the switch for regulating current range shall be adjusted to the most advanced position,so as to avoid instrument damage by measuring the instrument without selecting the range.
Fig.6-20 shows the use of tong-type ammeter.
Fig.6-20 Use of Tong-type Ammeter
5.Precautions for Storage of Tong-type Ammeter
(1)The tong-type ammeter shall be stored in a well-ventilated,dry and clean environment,and put on shelves.
(2)Properly maintain instruments and apparatus.
(3)Properly keep technical data and instructions of instruments and apparatus.
(4)The tong-type ammeter shall be maintained regularly.During maintenance,first check whether there is any damage to all components and parts of the meter appearance,wipe off the floating dust with a soft brush or cotton cloth,then carefully wipe and dry it with a little non-corrosive solvent or clean water.During maintenance,the battery box can be opened for inspection or scrubbing,but the meter shell cannot be opened.
(5)If the tong-type ammeter is internally equipped with a battery,it must be taken out to prevent the battery from leaking and damaging the ammeter.
(6)The indoor light for the tong-type ammeter shall not be too strong,and direct sunlight is strictly prohibited on the ammeter,because it will accelerate the aging of its plastic shell under the action of sunlight,while direct sunlight shall be prevented for the liquid crystal display screen.Fig.6-21 shows a tool cabinet for storing tong-type ammeter.
Fig.6-21 Tool Cabinet for Storing Tong-type Ammeter
6.Preventive Test of Tong-type Ammeter
The preventive test type of tong-type ammeter is mainly to check tong-type ammeter regularly.The checking period is usually 3 months,or it shall be checked after the meter is continuously used for multiple times.