A megohmmeter, also known as a shaker or insulation resistance tester, is a simple and commonly used direct reading instrument for measuring high resistance. It can be used to measure the insulation resistance of circuits, motor windings, cables, electrical equipment, etc. On the megohmmeter, there are three terminals labeled with grounding (N), circuit (U), and protective ring (G). When using, not only should the wiring be correct and the terminals be tightened, but also the following precautions should be taken:

1、 Before measurement, conduct an open circuit and short circuit test on the megohmmeter to check if it is functioning properly. The specific operation is: open the two connecting wires, shake the handle pointer to point to infinity, and then short the two connecting wires again, the pointer should point to zero.  

2、 The tested equipment must be disconnected from other power sources, and after the measurement is completed, the tested equipment must be fully discharged (about 2-3 minutes) to protect the equipment and personal safety.  

3、 The megohmmeter and the tested equipment should be separately connected using a single wire, and the surface of the circuit should be kept clean and dry to avoid errors caused by poor insulation between wires.  

4、 During shake testing, place the megohmmeter in a horizontal position and ensure that there is no short circuit between its terminals when the handle rotates. When shaking capacitors and cables, the wiring must be disconnected only when the handle is turned, otherwise reverse charging will damage the megohmmeter.  

5、 When shaking the handle, it should gradually increase in speed and accelerate evenly to 120r/min, and be careful to prevent electric shock. During the shaking process, if the pointer has already reached zero, it cannot continue shaking to prevent the coil inside the watch from heating up and being damaged.  

6、 To prevent surface leakage resistance of the tested equipment, when using a megohmmeter, the middle layer of the tested equipment (such as the inner insulation between cable shell cores) should be connected to the protective ring.  

7、 Suitable insulation resistance testers should be selected based on the voltage level of the tested equipment. For equipment with a rated voltage below 500 volts, a 500 volt or 1000 volt megohmmeter should be used; For equipment with a rated voltage of 500 volts and above, a megohmmeter with a voltage range of 1000~2500 volts should be used. The selection of measuring range should generally be careful not to exceed the insulation resistance value of the measured equipment too much, in order to avoid significant errors in readings.  

8、 It is prohibited to use a megohmmeter for measurement in thunderstorm weather or near equipment with high-voltage conductors.