So what are the safety protection designs for multimeters?
The multimeter is connected in parallel with the component under test. The multimeter acts as a shunt, which requires a large internal resistance. The multimeter is connected in series with the device under test to function as a voltage divider, and the internal resistance of the multimeter is required to be small. Once the connection is wrong, for example, in the current test mode, put the multimeter at both ends of the device under test. The branch where the multimeter is located will short-circuit the circuit because of the small internal resistance. The fuse may be blown, causing danger.
The other type is potential safety hazards, such as electric shock caused by accidental contact with live parts, transient high voltage caused by switching and load startup, etc. As power distribution systems and loads become more complex, the possibility of instantaneous overvoltage increases greatly. Equipment such as motors, capacitors, power converters, and variable frequency speed regulators are the main sources of spikes. In addition, lightning strikes on outdoor transmission lines can also cause very dangerous high-energy instantaneous high voltages. When measuring power systems, this instantaneous high voltage is often invisible, but it does exist and is difficult to avoid, and its potential dangers are also greater. These situations are often encountered even in low-voltage measurements, and the instantaneous voltages generated can reach several thousand volts or more. Therefore, when operating a multimeter, you must not only pay attention to correct wiring to reduce unnecessary danger or damage, but also avoid potential dangers through some safety designs.
So what are the safety protection designs for multimeters?
The first category is the external protection of the multimeter, such as double-layer isolation insulation protective sleeve, probe anti-contact protection, insulation protection of plugs and sockets, etc. However, to avoid the harm caused by instantaneous high voltage, safety must be deep inside the digital multimeter. In other words, there must be sufficient safety design inside the digital multimeter. Therefore, the IEC (International Electrotechnical Commission) has defined a new set of international safety standards specifically for testing instruments. Previously, the IEC348 standard was used, which has been replaced by IEC1010. The safety indicators of multimeters designed based on the new standard IEC1010 are much higher than those based on IEC348.
