Is the multimeter measuring voltage in parallel and how to measure it
First of all, we can find a dry cell battery, we all know that a 5 dry cell battery can provide 1.5 volts of DC voltage, at this time we just need to adjust the multimeter gear to DC voltage 2V gear can be, and then the red needle of the multimeter will be inserted into the VΩ holes, the black pen is inserted into the COM holes, with the black pen connected to the negative terminal of the battery, the red pen is connected to the positive terminal of the battery, the display should appear on the screen 1.5V or so, this is the voltage of this dry cell.
As for the potential in the board, we need to estimate the size of the measured potential first, and choose a range larger than the estimated potential, such as DC 5V, we need to choose DC 20V range, so as to avoid the measured potential higher than the range caused by the damage of the multimeter. Connect the black pen to the earth wire on the board, the earth wire can be found by checking the copper foil, which usually appears in pieces, and connect the negative pole of the electrolytic capacitor used for filtering to find the earth wire, then connect the red pen to the measured potential point and read the value. (The difference between potential and voltage can be found in my article).
Measuring 220V AC, this is a bit dangerous, so we need to keep our mind highly concentrated to avoid electric shock. Because it is AC power, we need to adjust the multimeter gear to AC voltage 750V gear, and then use the red and black pens of the multimeter to connect the fire line and zero line respectively, and read the value on it.
How to measure the main board of a gas water heater with a digital multimeter
Gas ignition is generally two battery-powered DC ignitors. Rarely bad, the situation is the iron tip no arc (spark). The reason is that the rust is not conductive, take out a few touches with sandpaper. Or change a copper wire is more resistant to burning. Because in the use of burning hot water, that fire mouth is always burning, time often rust. Output voltage 5 to 9v, multimeter to DC gear, the line is positive, inside the "s" bend is negative. You can also use the black pen to hit the negative pole of the battery and the red pen to hit the ignition line (the line that spits sparks). In some cases, the oxidised and rusted tube inside also leads to the absence of sparks (because it is the negative pole). (Because it is negative). The above test is normal, is the problem of water pressure is too small.
