Structure of pointer multimeter and measurement of current and voltage
Multimeter is a multifunctional, multi-range measurement instrument, general multimeter can measure DC voltage, DC current, AC voltage, resistance and audio level and other electrical quantities. Some multimeters can also measure AC current, capacitance and inductance, as well as some parameters of semiconductors (diodes, etc.), and with the emergence of digital display multimeters, measurement is more convenient. Pointer multimeters are still widely used because of their simple structure, cost-effectiveness, and intuitive performance. The following on its structure and the current, voltage measurement methods and some brands with you to exchange a little.
Structure of pointer multimeter
Meter head:
And used to display the value of the part, is a high sensitivity magneto-electric DC ammeter, the multimeter "heart" is called, is used to indicate the measured value, the main performance indicators of the multimeter basically depends on the performance of the head. The sensitivity of the head refers to the DC value flowing through the head when the pointer of the head is deflected to full scale, the smaller this value is, the higher the sensitivity of the head is, and the higher the internal resistance is when measuring voltage, the better the performance of the multimeter is.The sensitivity of the MF series pointer multimeter is around 10~1000 microamps.
Measurement circuit: The measurement circuit is used to convert various measured quantities into DC micro-current suitable for meter measurement, which consists of resistors, semiconductor components and batteries, and it will be a variety of different measured quantities, different ranges, after a series of processing, such as rectification, shunt, etc., and united into a certain amount of DC current limit is sent to the meter head for measurement.
Transfer switch: the role of the transfer switch is used to select a variety of different measurements of the circuit to meet the requirements of different types and different ranges of measurement. When the switch is in a different position, its corresponding fixed contacts are closed, the multimeter can become a variety of different ranges of electrical measuring instruments.
The shape of the pointer multimeter can be seen on the panel of the multimeter is equipped with a scale, the switch knob, zero knob and the measurement of the pen socket and so on.
The use of pointer multimeter
When using the multimeter, you should be familiar with the meaning of various symbols on the instrument panel and the main role of each knob and selector switch, you should check whether the pointer is pointing at zero, such as not at zero, you can adjust the mechanical zero adjuster on the table cover, so that the pointer to restore the zero position. Then according to the measured type and size, rotate the selector switch to the corresponding gear and find out the corresponding scale on the dial of the pointer.
Measurement of voltage and current
As with measuring voltage and current with a voltmeter and ammeter, a pointer multimeter should be connected in parallel in the line when measuring voltage, and a multimeter should be connected in series in the line when measuring current. Also, when measuring DC voltage and current, note the polarity of the 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 get an accurate reading. The range should be greater than the value being measured or the meter may be damaged.
Measurement of resistance
Select the appropriate magnification gear: when measuring resistance, the choice of magnification gear so that the pointer stays in the thinner part of the scale is appropriate. The closer the pointer is to the middle of the scale, the more accurate the reading; the more to the left, the more crowded the scale line, the worse the accuracy of the reading. The multiplier block should be smaller than the measured value. Zero: Before measuring resistance, the test pens should be touched together, colleagues rotate the "zero knob" (as shown in the figure above the right edge of the multimeter on the right edge of the larger knob), so that the pointer just points to the zero position of the ohm scale, this step is known as the ohm file "zero". ". Every time you change the multiplier block to measure the resistance before, have to repeat this step, which is to ensure the accuracy of the measurement of essential steps. If the pointer can not be adjusted in place, indicating that the battery voltage is insufficient or the instrument circuit has a problem. Can not be charged resistance measurement: measurement of resistance, the multimeter powered by the battery, the measured resistance must not be able to be charged, because charged measurement is equivalent to access to an additional power supply, not only do not get the correct measurement data, but also may damage the head. The actual value of the measured resistance which comes: the actual value of the measured = multiplier × pointer reading. Such as in the 1000 multiplier block on the measurement of resistance readings for 25, then the measured resistance value of 25 × 1000 = 25000 ohms.
