How multi meter works. Seek professional 40

This belongs to the meter head modified into a large number of ammeters and voltmeters, the first and second joints you said are modified into a large range of ammeters, in the ammeter modification, it should be noted that the maximum current through the meter head is ig can not be changed, so if more current through the newly modified ammeter, a resistor must be connected in parallel, so that a part of the current passes through the resistor in parallel, which is the so-called shunt effect. Take an example, if the resistance of the meter head is 30 ohms, and now there is a resistance of 1 ohm in parallel with it, then in the case of the same voltage in parallel, when the maximum current through the meter is IG, there will be 30IG current through the resistance of 1 ohm, and a total of 31IG of current will pass through the new meter, and the range will be expanded to 31 times of the original, if it is in ohms in parallel, when the maximum current through the meter head is IG, there will be 300IG of current through the resistance of 300 ohms, which is equivalent to an expansion of 301 times. Therefore, the smaller the resistance of the parallel connection, the more it will be shunted, and the larger the range of the new meter.

What you say can only be theoretically passed, but also in connection with the actual consideration, if you want to measure a large current, you need to use a transformer, maybe the meter you are talking about is the current measured by the transformer.

1.The principle of multi-metering.

1) The use of multi-meter: in the DC power supply circuit, the voltage of a certain two points of the circuit is measured, and the current in the circuit is measured.

The core of the multimeter is composed of a DC sensitive galvanometer g (i.e., the meter head), resistance and toggle transfer switch.

Flip the selector switch to contact 1 or 2 for the DC measurement end.

Flip the selector switch to contact 3 or 4 as the DC measuring end.

Flip the selector switch to contact 5 as the measuring end.

3) Multi-meter voltage block, current block and ohm block.

The principle of measuring DC current and voltage with multiple electric meters is the same as that of ammeters and voltmeters, which is essentially the principle of shunt resistance shunt and series resistance shunt. Note: When reading, read the scale value corresponding to the select switch gear.

r5+r6)=r, which is the zeroing resistance. When the resistor Rx to be measured is connected to the common terminal and the measuring terminal 5, a closed circuit is formed, and the current value on the dial can be changed to the resistance value according to the relationship between Rx and the circuit current i, and the resistance value of the resistor Rx to be measured can be obtained.

When no resistor is connected (open state, rx), the current is i=0, the hand is not deflected, and the leftmost end of the dial indicates the resistor.

ii When the two pens are directly connected (short-circuit state, rx=0), the current i is the full bias current, the hand points to the maximum value, and the rightmost end of the dial indicates that the resistance is 0.

2.Surface structure of a multi-meter:

1) The upper part is the dial, with a total of three tick marks.

The left end of the top tick mark is marked with 0 at the right end, which is used to measure resistance.

The middle tick mark is used to measure DC current and DC voltage, and its scale is evenly distributed.

The left side of the bottom tick mark is used to measure AC voltage, and its scale is uneven.

2) The lower part is a selector switch, and the area and range of the measurement function are marked around it. Rotate the selector switch of the multi-meter to the current block, and the multi-meter will measure the current; When the selector switch is rotated to a different functional area, the voltage or resistance can be measured.

3) There is also a pair of positive and negative jacks on the surface of the multi-meter. Red watch pen plug + jack, black watch pen plug - jack, the knob on the jack is called ohm zeroing, with which the resistance can be zeroed, in addition, there is a mechanical zero adjustment between the dial and the selection switch, with which it can be used for mechanical zeroing, that is, rotating the zeroing screw, so that the pointer (when not connected to the circuit) points to the left end of the 0 engraved line.

The principle and use of multi-meter are as follows:

1. The principle of multi-meter.

1) The principle of measuring DC current and DC voltage is the same as that of DC ammeter and DC voltmeter.

2) Measuring resistance: The principle of the internal circuit is shown in the figure on the right, and its principle is measured according to Ohm's law of the closed loop, that is, i=e (rg+r+r+rx), in which all are fixed-value resistances, and different rx correspond to different currents i (of course, the relationship between current i and the measured resistance rx is not proportional, so the scale of the resistance value is not uniform). If the resistance Rx value corresponding to the current i is directly marked on the dial, the resistance value of the measured resistance can be read directly from the dial.

(3) "Zeroing" principle: when the two meters are in contact, rx=0, the current is adjusted to the full offset value (maximum), and the corresponding resistance value is zero.

4) The median resistance is the internal resistance of the multi-meter resistance file, when the measured resistance rx=rg+r+r, the current through the meter head, that is, the current through the meter head is half of the full bias current, at this time the pointer points to the ** of the dial, so the internal resistance of the resistance file is generally called the median resistance.

2. How to use the multi-purpose table.

1) When measuring the current, like the ammeter, the multimeter should be connected in series in the circuit under test, and for direct current, the current must flow from the red meter pen into the multimeter and out of the black meter pen.

2) When measuring voltage, like the voltmeter, the multimeter should be connected in parallel at both ends of the circuit under test, for direct current, the red meter pen must be connected to the point with higher potential, and the black meter pen must be connected to the point with lower potential.

(3) When measuring the resistance, after selecting the gear, the two watch pens should be in contact with each other, adjust the zero knob of the resistance file, so that the pointer points to the zero position of the resistance scale, and then connect the two watch pens with the two ends of the resistance to be measured. It should be noted that when switching to another range in ohms, the zeroing knob of the resistance level needs to be readjusted in order to take the measurement.

The principle and use of multi-meter are as follows:

1. The principle of multi-meter.

Multi-meter meters can be used to measure current, voltage, resistance, etc., and each measurement has several ranges. The principle on which the current and voltage measurement of multi-meter is based is the characteristics of series and parallel circuits and Ohm's law of some circuits. The ohmmeter is the resistance measurement block of the multimeter.

The principle on which ohmic meters measure resistance is Ohm's law for closed circuits.

2. Instructions for the use of multi-meter:

Mechanical zeroing inserts the red and black watch pens into the "+" jack respectively. Use a small screwdriver to turn the mechanical zeroing knob until the pointer points to zero. When measuring the current, turn the selector switch to the current stop, and select the appropriate range according to the estimated current.

The voltage measurement will connect the meter in parallel at both ends of the circuit to be measured, the red table pen will be connected to the high potential, and the black meter pen will be connected to the low potential.

Measure the resistance of the resistor to be measured, select the appropriate ohmic gear, and make the pointer point to the zero position of the ohmic scale. The measurement and reading will be connected to the red and black watch pens respectively with the two ends of the resistance to be measured, and the number of the watch hand is multiplied by the magnification of the selected ohmic stop, which is the resistance value of the resistor.

Precautions for multi-meter: Do not rotate the range selection knob during the test. The watch pen must be inserted into the jack of the multi-meter in strict accordance with the color, red is "+" and black is "-" When measuring, the human body must not touch the metal parts of the meter pen, so as to ensure the accuracy of the measurement and personal safety.