Checks before using a multimeter to measure
The multimeter is a multi-functional and multi-range measuring instrument, and it is always inseparable from the electronic and electrical technology. General multimeters can measure DC current, DC voltage, AC current, AC voltage, resistance and audio level, etc., and some can also measure capacitance, inductance and some parameters of semiconductors (such as β). If it is simply distinguished by the display method, the multimeter can be divided into a pointer multimeter and a digital multimeter.
The three basic functions of the multimeter are to measure resistance, voltage, and current, so the old-timers call it a three-purpose meter. Many new functions have been added to the current multimeter, especially the digital multimeter, such as measuring capacitance value, transistor magnification, diode voltage drop, etc. There is also a talking digital multimeter that can broadcast the measurement results in language.
Steps
Check whether the battery voltage and power generation are normal and whether the battery pile head is seriously rusted. Many car owners think that the result of the leakage is a battery problem or a generator problem;
Ask the car owner if they have repaired, installed anything or disassembled in a collision recently;
Remove the negative pole of the battery, turn the multimeter to the maximum current range, connect the red test lead to the negative line, and connect the black test lead to the battery pile head and fix it;
Turn off all electrical appliances inside and outside the car, lock the door, observe the current level, adjust to the appropriate gear, and record;
Wait for about 20 minutes; after all the modules of the vehicle enter the dormant state, read the accurate static discharge current;
The quiescent current is generally 0.03A (ie 30mA), please refer to the maintenance manual for details, and it should not exceed 50mA;
If the quiescent current is too large (as shown in the figure above), we can check by pulling out the insurance and the relay, that is, unplug the insurance one by one, and observe the magnitude of the quiescent current;
Check before measurement
Observe whether the pointer of the multimeter is set to 0. If it is not at 0, turn the zero adjustment screw to set it to 0.
Check the integrity of the two test leads and leads. This point is especially critical when measuring higher AC voltages to prevent electric shock accidents.
Check the lead wire plug, if it is loose, try to fasten it. Sometimes the looseness is caused by the looseness of the fastening nut of the socket. At this time, the watch case must be opened and repaired.
