Method of measuring DC voltage and current with a digital multimeter
Readings should look at the "dc" or "v-ma" symbol of the scale, the knob refers to the value of the maximum limit of DC voltage or current (range). Measurement should be estimated before the size of the measured value, and then turn the switch to the appropriate limit of the gear. The size of the measured value can be read out proportionally. When measuring the voltage between two points on the circuit, the red test pen should be connected to the high potential point and the black test pen should be connected to the low potential point. When measuring DC current, the ammeter should be strung into the branch circuit, so the branch circuit under test must be disconnected first.
If there is no broken branch circuit on the two pens to the two endpoints of the branch, in fact, the ammeter to measure the voltage, the meter that is burned. Judge the quality of capacitors with a multimeter depending on the size of the electrolytic capacitor capacity, usually choose the multimeter r × 10, r × 100, r × 1k block test judgement. The red and black pens are connected to the negative pole of the capacitor (before each test, the capacitor needs to be discharged), by the needle of the pendulum to judge the quality of the capacitor.
If the needle swings up quickly to the right, and then slowly to the left back to the original position, generally speaking, the capacitor is good. If the meter needle swings up and then no longer turns back, it means that the capacitor has been broken. If the meter needle swings up and then gradually returns to a position to stop, it means that the capacitor has been leaking. If the needle does not swing up, the capacitor electrolyte has dried up to push the loss of capacity.
Some leakage capacitors, with the above method is not easy to accurately determine the good and bad. When the capacitor's withstand voltage value is greater than the value of the battery voltage in the multimeter, according to the electrolytic capacitor positive charging leakage current is small, reverse charging leakage current is large characteristics, you can use the r × 10k block, the capacitor for the reverse charging, and observe the meter needle stays at the stability (i.e., whether the reverse leakage current is constant), and thus determine the quality of the capacitor, the accuracy of the higher degree. Black pen connected to the negative terminal of the capacitor, red pen connected to the positive terminal of the capacitor, the meter needle quickly swing up, and then gradually back to a place to stay still, it is good to show that the capacitor, where the meter needle in a position to stay unstable or stay and then gradually and slowly move to the right of the capacitor has been leakage, can not continue to use. The meter needle generally stays and stabilises in the range of 50-200k scale.
