Modification of the pointer AC clamp current table, CLAMP Meter
Keywords: modification of pointer AC clamp current table
Modification of pointer AC clamp current table
Author: He Jiahua
The AC clamp current table is relatively convenient and safe, but the lower limit of the measurement is high. Generally, the small pointer clamp current table has a measurement current of 1A. If the 30V home appliance or appliance power is 220W, it is difficult to distinguish. It is necessary to measure the standby power consumption of the TV. In order to measure the smaller current of 10mA of the electrical equipment, it is necessary to add an amplifier. Here is the MG26 type clamp table produced by the modified Hang-out L., which can measure 10mA to 30A current and 300V AC voltage for your reference.
As shown in FIG. 1, the current is measured by the current transformer L, and the quantial switch is connected in parallel with one of the shunt resistors RL to R5, and the generated pressure drop is sent to A0 amplification, and the RLO can change the magnification, The overall value of the current meter, A1, VDL, VD2, VD3, and R15, etc. constitutive linear rectifier circuits, and rectify the signal from C2. This circuit is more than a common circuit, and R15 is added to enhance the compensation effect of small signals, and then filter through the filter composed of R16 and C3, and then output indication of the current table. R17, R18 is a static zero circuit. Vim, VD5, R19 and current tables form an AC voltmeter.
Installing the measurement data for some large currents in the unmarkable to note the measurement data of some large currents to modify the calibration. The surface scale, current and voltage of the modified clamp table are shared with the original voltage reading, and the original current scale is not used. To reduce the trouble and unrestrained. The mutual control coil L uses the original, the button switch K2 is placed under the jaw spring, and the shunt resistors R1 to R5 are mounted to the routine switch, and the range switch is connected to the double-knife six case to reduce the switch contact resistance when the measurement 30A is measured. The error caused. The battery is placed on the circuit board in the position of the original circuit board, and the battery uses a 23A type φ10mmx29mm 12V small battery section.
The debug is based on 60mA blocking benchmark. R10 uses 100kΩ, R15 with 20KΩ, R17 with a 200Ω adjustable resistor replace, the power source does not input the measurement current, and the R17 is adjusted to zero N position, which indicates that the table needle indicates 0, indicating The output offset voltage is small. At this time, the R17, R18 can be removed, and the VD5 and the current table negative are directly grounded, otherwise the adjustable R17 allows the output indication to 0. The (1) foot voltage is then measured is around 1/2 of the power supply voltage. If the deviation is too far, adjust the resistance of R8. Then enter the measured current (as shown in Figure 2). Note that the clamp table jaw is left away from the transformer over 60 cm or more, otherwise the transformer's leakage will generate interference. The jaws do not clamp the wires will have an output indication (using this phenomenon to compare the magnetic size of the transformer), the measured line is in the center of the jaw. If the 60mA current is measured, the R10 indicates the output indication, then measures 2, 4, 6, 8, 10, 20 mA current, respectively. If the indication is large, if the indication is large, it is necessary to adjust the R15 resistance; indication is small, turn the R15 resistance, and must be re-calibrated each time the R15 must be re-calibrated, repeat it several times until adjustment, replace it Fixed resistance.
The corresponding current values are measured separately, and the RL ~ R5 is adjusted, and it is accurate.
Measure the 300V voltage gear and input with the original socket. Do not press the power switch K2 when used, and the current score switch can be placed at any gear. When adjusting the digital multimeter and the main meter simultaneously measure the mains, adjusting R19 makes its indication. R19 uses 100KΩ resistor and LMΩ adjustable resistance series, pay attention to safety when debugging.
The power supply voltage from 6V to 12V can be compressed from 6V to 12V, and the current is about 580 μA when using 12V.
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