To use a multimeter as an ohmmeter, follow these steps
① When measuring, zero should be set first. Directly touch the two probes (short circuit), adjust the dial - the zero ohm adjuster below to correctly point the pointer at zero ohm. This is because as the use time of the internal dry battery increases, the power supply voltage it provides will decrease. When Rx=0, the pointer may not reach full bias. At this time, it is necessary to adjust Rw to reduce the shunt current of the meter head, in order to meet the requirement of full bias current Ig.
② In order to improve the accuracy of testing and ensure the accuracy of the tested object, it is necessary to select the appropriate range range correctly. When measuring resistance, it is required that the pointer be within the range of 20% to 80% of the full scale, so that the testing accuracy can meet the requirements.
③ Due to different range ranges, the magnitude of the test current flowing through only Rx also varies. The smaller the range range, the greater the test current; otherwise, the opposite is true. So, if the small range ohmic range RX1 and RX10 of a multimeter are used to measure the small resistance Rx (such as the internal resistance of a milliampere meter), a large current will flow through Rx. If this current exceeds the allowed current of Rx, Rx will burn out or bend the pointer of the milliampere meter. So when measuring resistance that does not allow large currents to pass, the multimeter should be placed on the ohmic range with a large range. The larger the range range range, the higher the voltage of the dry battery connected to the internal resistance. Therefore, when measuring resistance that cannot withstand high voltage, the multimeter should not be placed on the Ohm range with a large range. When measuring the inter pole resistance of a diode or transistor, the ohm range should not be set to the Rxl0k range, otherwise it is easy to cause inter pole breakdown of the transistor. Only lower the range range and let the pointer point at the high resistance end. But as mentioned earlier, the resistance scale is non-linear, and the scale at the high resistance end is very dense, which can easily cause an increase in error,
When using a factory made ohmmeter, connect it to a dry battery, the negative pole of the battery, and the black probe to the positive pole of the dry battery. For external circuits, the red probe is connected to a dry battery
When measuring a large resistance, hands should not touch both ends of the measured resistance at the same time. Otherwise, the human body resistance will be connected in parallel with the measured resistance, resulting in incorrect measurement results and a significant reduction in the test value. In addition, when measuring the resistance on a circuit, the power supply of the circuit should be cut off. Otherwise, not only will the measurement result be inaccurate (equivalent to connecting an external voltage), but it will also cause a large current to pass through the microampere meter head, causing the meter head to burn out. At the same time, one end of the measured resistance should be soldered off the circuit before measurement, otherwise the total resistance of the circuit at that two points will be measured.
(6) Do not place the range switch on the ohm range after use.
In order to protect the microampere meter head and prevent accidental burning of the meter head during the next measurement. After the measurement is completed, attention should be paid to turning the range switch to the maximum range position of DC or AC voltage, and never place it on the ohm range to prevent the internal dry battery from being completely depleted when the two probes are short circuited.
