Problems with Uni-T multimeters

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Problems with Uni-T multimeters [Copy link]

A multimeter is an important tool for maintenance personnel. I personally prefer to use the Uni-T, which is better than the Victory meter.

It is more convenient to use an automatic meter for circuit board repair. I used UT71C, UT171A and UT61E+ meters.

The three meters are different. When measuring the resistance of the same IC pin on the circuit board, the impedance values displayed are different. Of course, when measuring the resistance value, the measured values of the three meters are the same.

When measuring impedance that is not a standard resistor, the measured values of three different models of meters are different, and the measured values of meters from different manufacturers are also different.

When UT71C has saved data, the display value fluctuates once the save button is pressed manually. The number of saved values is 100, which is too small. When using the DC voltage range to measure the high-voltage switch circuit of the power amplifier, the DC voltage range cannot automatically shift and displays a very small voltage value. The manufacturer's solution is to manually select the DC voltage range to measure the DC voltage of the switch.

The industrial-grade UT171A meter measures the capacitance of electronic components, but often there is no measurement value and the capacitance measurement is inaccurate. This was also the case after I sent my meter back for repair.

The buttons for manually saving measurement data are not flexible enough. The buttons on the table have to be pressed hard. Automatic saving is not possible during manual measurement. There is no time prompt during automatic saving, and it is difficult to coordinate the time for manually changing the measurement position with the automatic saving time.

It seems that the manufacturer focuses on automatically saving data and does not consider the inconvenience of manual saving by the operator.

The UT61E+ meter is not accurate when measuring frequency, it cannot automatically shift gears when measuring switch voltage, and it is better to connect a capacitor in series with the meter pen when measuring frequency. When measuring the impedance of the same electronic component, the measurement value of 61E+ is the smallest, and the difference is quite large.

When measuring the components of the circuit board with the resistance range of UT61E+ and UT171A, the measured value always cycles between M and K ohms. There are no large capacitors or inductors on the circuit board, and the impedance value of the component pins is unknown. If the same measurement point or the circuit board has parallel pins, the measured value will be different each time if measured several times.

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Another major disadvantage of the UT meter is that the battery is not durable. If you use it too much, the battery will be worn out in a week.

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Use UT171A to measure the resistance of the chip 74LS245 pin to ground. Turn the meter to the resistance measurement and it is 1.35M ohms. Press the maximum value button and the dial displays MAX. Then measure the same pin and the resistance value displayed on the meter is 2.62M. The circuit board is removed and 245 is bus data transmission, which is equivalent to the chip pin being suspended.

Just by selecting a MAX/MIN button, the measured value changes so much.

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Use UT61E+ to measure the resistance of the 74LS245 pin on the circuit board. The recording order is that the upper row of data is from pin 1 to pin 10, and the measured resistance value is stable. The lower five rows are the resistance values of pins 11 to 20. After repeated measurements, the resistance value is unstable and jumps horizontally.

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This circuit board is good, the IC is also good, and the values of the 8 B pins measured by UT171A are similar and nearly equal.

The output and input of 74LS245 are 74LS273