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How to properly use a multimeter, a shake meter, a clamp meter, and a multimeter?
The concept of multimeter: it is also called multimeter, three-use meter, multiplex table, it is a multi-function, multi-range measuring instrument, general multimeter can measure DC current, DC voltage, AC voltage, resistance and audio level, etc. It can also measure AC current, capacitance, inductance, and some parameters of the semiconductor (eg, β).
1. The structure of the multimeter (500 type) multimeter consists of three main parts: measuring circuit, header, and switch.
(1) Measurement circuit The measurement circuit is a circuit that converts various measured DC currents that are suitable for meter measurement. It consists of a resistor, a semiconductor element, and a battery.
It can convert all kinds of different measured (such as current, voltage, resistance, etc.) and different ranges through a series of processes (such as rectification, shunting, partial pressure, etc.) into a certain amount of tiny DC current. Header for measurement.
(2) Header: It is a high-sensitivity magnetoelectric DC current meter. The main performance indicators of a multimeter basically depend on the performance of the meter head. The sensitivity of the meter refers to the value of the DC current flowing through the meter when the meter pointer is full-scale deflection. The smaller the value, the higher the meter's sensitivity. The greater the internal resistance when measuring the voltage, the better the performance. There are four tick marks on the meter. Their functions are as follows: The first (from top to bottom) is marked with r or ω, indicating the resistance value. When the switch is in the ohmic range, it reads the tick mark. The second bar marked with ∽ and va indicates the AC and DC voltage and DC current value. When the switch is in the AC and DC voltage or DC current range, the range reads other than the AC 10V. line. The third is marked with 10v, which indicates the AC voltage value of 10V. When the switch is in AC and DC voltage range, and the range is in AC 10V, read the tick mark. The fourth bar, labeled db, indicates the audio level.
(3) The function of the change-over switch is to select various measurement lines to meet the measurement requirements for different types and different ranges. There are generally two switchers, each marked with a different gear and range.
2. Symbol Meaning (1) 45-65-1000hz indicates that the frequency range of use is below 1000hz, and the standard frequency range is 45-65hz.
(2)2000ω/vdc indicates the sensitivity of the DC block is 2000ω/v
The symbols on the Clamp and Dial are similar to the above symbols (otherwise, because the symbol format is incorrect, not all of the “representing magneto-mechanical rectification mechanical counterforce instruments†means that the third-grade anti-magnetic field “denotes horizontal placementâ€).
(3) a-v-ω means measurable current, voltage and resistance (4) ∽ indicates AC-DC (5) v-2.5kv 4000ω/v means that for AC voltage and 2.5kv DC voltage block, the sensitivity is 4000ω/v
3. The use of a multimeter (1) According to the type and size of the measurement, select the gear and range of the switch to find the corresponding tick.
(2) Select the location of the test leads.
(3) Familiar with the meaning of each symbol on the dial and the main role of each knob and selector switch.
(4) Measuring voltage: When measuring voltage (or current), choose a good range. If you use a small range to measure a large voltage, there is a danger of burning the meter; if you use a large range to measure a small voltage, then the pointer deflection is too small. Unable to read. The range should be chosen so that the pointer is deflected to about 2/3 of full scale. If you do not know in advance the size of the measured voltage, you should first select the highest range of gear, and then gradually reduce to the appropriate range.
a. AC voltage measurement: put one switch of the multimeter into AC and DC voltage block, and the other switch is placed on the appropriate range of AC voltage. The two pens of the multimeter and the circuit under test or load can be connected in parallel.
b. Measurement of DC voltage: Place one switch of the multimeter on the AC and DC voltage block, and another switch on the appropriate range of DC voltage, and the “+†meter (red pen) receives high potential. -" The test pen (black pen) receives a low potential, that is, let the current flow from the "+" meter pen and out of the "-" meter pen. If the test leads are reversed, the head pointer will be deflected in the opposite direction and it is easy to knock the pointer.
(5) Measuring the current: When measuring the DC current, place one of the multimeter's switches in the DC current block and the other switch in the proper range of 50 ua to 500 mA. The current range selection and reading methods are the same as the voltage. During the measurement, the circuit must be disconnected first. Then follow the direction of the current from “+†to “-†to connect the multimeter in series to the circuit under test. That is, the current flows in from the red meter and flows out from the black meter. If you accidentally connect the multimeter in parallel with the load, the internal resistance of the meter will be too small and it will cause the short circuit to burn the instrument. Its reading method is as follows:
Actual value = indication value × span / full deflection (6) Resistance measurement: When using a multimeter to measure resistance, the following methods should be used:
a. Select the appropriate override block. The scale of the ohmmeter of the multimeter is not uniform, so the selection of the override should make the pointer stay in the dilute part of the scale. The closer the pointer is to the middle of the scale, the more accurate the reading. In general, the pointer should be between 1/3 and 2/3 of the scale.
b. Zero the ohms. Before measuring the resistance, the two test leads should be short-circuited and the “ohm (electrical) zero adjustment knob†should be adjusted at the same time so that the pointer just points to the zero position to the right of the ohmic graticule line. If the pointer cannot be set to zero, the battery voltage is insufficient or there is a problem inside the instrument. And every time you replace the override block, you must perform ohmic zero again to ensure accurate measurement.
c. Reading: The reading of the meter multiplied by the magnification is the resistance of the measured resistance.
(7) Perform mechanical zero adjustment.
(8) Precautions:
a. When measuring current and voltage, it is not possible to electrify the range. b. When selecting the range, select the largest one and then the smallest one. Try to make the measured value close to the range. c. When measuring the resistance, the live measurement cannot be performed. Because the multimeter is powered by the internal battery when measuring resistance, if it is charged, it is equivalent to connecting an extra power supply, which may damage the meter.
d. After use, the switch should be in the maximum gear or neutral gear of AC voltage.
Digital multimeters have become mainstream, with the trend of replacing analog meters. Compared with analog meters, digital meters have high sensitivity, high accuracy, clear display, strong overload capacity, easy portability, and simpler use. The following uses the vc9802 digital multimeter as an example to briefly introduce its use methods and precautions.
(1) How to use:
Before use, you should carefully read the relevant operating instructions, familiar with the power switch, range switch, jack, special socket role.
Set the power switch to the on position.
* AC and DC voltage measurement: According to the needs of the range switch dial to dcv (DC) or acv (AC) of the appropriate range, red table pen into the v / ω hole, black table pen into the com hole, and the test lead in parallel with the line under test, The reading is displayed.
* Measurement of AC and DC current: Set the range switch to the appropriate range of DCA or aca (AC), insert the red meter pen into the MA hole (<200ma) or 10a hole (>200MA), and insert the black pen into the com hole. And the multimeter can be connected in series in the circuit under test. The digital multimeter automatically displays polarity when measuring dc quantities.
*Measurement of resistance: Set the range switch to the appropriate range of ω, insert the red meter pen into the v/ω hole, and insert the black meter pen into the com hole. If the measured resistance value exceeds the maximum value of the selected range, the multimeter will display “1†and a higher range should be selected at this time. When measuring the resistance, the red pen is positive and the black pen is negative, which is exactly the opposite of an analog multimeter. Therefore, when measuring polar components such as transistors and electrolytic capacitors, the polarity of the test leads must be observed.
(2). Usage notes:
a. If it is impossible to estimate the magnitude of the measured voltage or current in advance, you should first dial the highest range and measure once, and then gradually reduce the range to the appropriate position. After the measurement is completed, set the range switch to the highest voltage level and turn off the power.
b. It is prohibited to change the range when measuring high voltage (above 220v) or high current (above 0.5a) to prevent arcing and burn the switch contacts.
c. When "", "batt" or "lowbat" is displayed, the battery voltage is lower than the operating voltage.
d. When measuring the voltage, connect the digital multimeter in parallel with the circuit under test. When measuring the current, it should be connected in series with the circuit under test. When measuring the amount of DC, it is not necessary to consider the positive and negative polarity.
e. At full scale, the meter only displays the digit "1" at the highest position, all other digits are gone, and a higher range should be selected.
f. When the AC voltage is used to block the measurement of DC voltage, or if the DC voltage is used to block the measurement of AC voltage, the display will show “000â€, or the digits on the lower digit will appear to jump.
Clamp meter is a meter used to measure the current of the running electrical circuit. It can measure the current without power.
1. Structure and principle The clamp meter essentially consists of a current transformer, a pliers wrench, and a rectifying magnetoelectric system with counteracting force.
2. Precautions (1) The voltage of the circuit under test should be lower than the rated voltage of the clamp meter.
(2) When measuring the current of the high-voltage line, wear insulating gloves, wear insulated shoes, and stand on the insulation mat.
(3) The jaws must be closed tightly without live switching.
3. Use method (1) Before measurement, mechanical zero adjustment (2) Measurement should be made in the center of the jaws of the wire under test, and close the jaws to reduce errors.
(3) After the measurement is completed, place the transfer switch at the most range.
(4) Choose a suitable range, select the largest, then select a small range or look at the value of the nameplate.
(5) When using the minimum range measurement, if the reading is not obvious, you can wind the measured wire several times. The number of turns should be based on the number of turns in the center of the jaw. Reading = indication value × range / full deviation × åŒnumber