Mechanical Pointer Multimeter Measurement of Voltage and Current
As with measuring voltage and current with a voltmeter and ammeter, the pointer multimeter should be connected in parallel in the line when measuring voltage, and the multimeter should be connected in series in the line when measuring current. Also, when measuring DC voltage and current, note the polarity of the meter pens (the general guideline is black for negative and red for positive). What is the maximum value likely to be in the range, or choose the largest range of the meter, and then gradually reduce the range in order to arrive at an accurate reading. The range should be greater than the value being measured or the meter may be damaged.
The actual value of the line being measured is determined by this formula: actual value = pointer reading × range / full bias scale
Where: full scale refers to the maximum scale value on the selected scale. For example: using a pointer multimeter to measure a DC voltage, the range selected as 100V, full bias scale of 50, the pointer points at 20, the actual value = 20 × 100/20 = 40V.
Measurement of AC contactor coil good or bad multimeter to play the ohm block which number is appropriate!
The size of the contactor is different, the parameters are different, in other words, the resistance value of the coil is different. Usually, it is tens of ohms to tens of thousands of ohms, and you can test it with different ohm stops of the multimeter. It's fine as long as it's easy to read the value yourself.
Usually, the coil of the contactor if it is not a short circuit, or open circuit. Is not very good to judge good or bad. Our usual test method, is to take a contactor model and the size of the contactor to be tested exactly the same. The two do a resistance comparison, will be able to judge the coil is good or bad. Because if a short circuit occurs between the turns of the coil, just a little change in the resistance value, using a multimeter simple measurement is unable to judge.
If the multimeter has 200 ohms, use 200 ohms to measure first, if the measurement is more than 200 ohms, use 1000 ohms or 2000 ohms to measure. The above is the domestic multimeter measurement method. If it is Fluke directly to the ohm gear is good!
