What issues need to be addressed when using the ohm range of a multimeter for measurement?
(1) Before measuring the resistance, it must be zeroed. Especially when changing the magnification of the ohm range, it is necessary to zero it. This is an essential step to ensure measurement accuracy. When the zero knob cannot make the pointer reach the zero position of ohms, it indicates that the battery voltage in the meter is too low and a new battery should be replaced.
(2) When measuring resistance, the tested circuit must not be energized. Otherwise, not only will the measurement results be inaccurate, but there is also a high possibility of burning out the meter head.
(3) The measured resistor cannot have parallel branches, otherwise the measurement result will be the equivalent resistance of the measured resistor in parallel with the parallel branch, rather than the resistance value of the measured resistor. For this reason, when measuring resistance, never touch the metal part of the probe with your hand to avoid unnecessary errors caused by parallel connection of human resistance to the two ends of the measured resistance, as shown in the figure (incorrect resistance measurement method).
(4) When measuring transistor parameters using Ohmic mode, considering that the voltage and current that the transistor can withstand are relatively small, it is generally recommended to choose a magnification mode of R × 10 or R × 1k. This is because the internal resistance of the low magnification gear is smaller and the current is larger; The battery voltage in high magnification mode is higher. So it is generally not suitable to measure the parameters of transistors in low or high magnification mode. It should be noted that the red probe of the pointer multimeter is connected to the negative terminal of the battery inside the meter, while the black probe is connected to the positive terminal of the battery inside the meter. This is different from a digital multimeter.
(5) The ohm range of a multimeter cannot directly measure instruments such as microampere meter heads, ammeters, standard batteries, etc. (because these instruments have extremely low internal resistance, they are prone to burning out when measured with the ohm range). During intermittent use, do not short-circuit the two probes to avoid wasting the battery.
