Practical Measuring Skills of Analog Multimeters
① Testing Speakers, Headphones and Dynamic Microphones: Use the R×1Ω range. Connect one test lead to one terminal, and briefly touch the other terminal with the second test lead. A clear and loud "click" sound will be heard for good components. If no sound is produced, the coil is broken. If the sound is faint and sharp, coil rubbing occurs and the component cannot be used. There are generally three methods, which are described in detail below.
Method 1: For meters without an hFE socket, or when the transistor package is too large to fit into the socket, this method may be used. For an NPN transistor, first identify the base b (it is easy to determine whether the transistor is NPN or PNP and locate its base pin). Set the meter to the R×1kΩ range. Connect the red test lead to the presumed emitter e (note: the hand holding the red lead must not touch the probe tip or transistor pin), and the black test lead to the presumed collector c. Hold the transistor and grip the probe tip and transistor pin with a finger. Touch the base b with your tongue; the meter pointer will deflect to a certain extent. If the leads are connected correctly, the deflection will be large; if the connection is wrong, the deflection will be small. The difference is obvious. You need to swap the leads and take two measurements, then compare readings to make the final judgment. This method applies to transistors of all package types and is convenient and practical. The amplification capability of the transistor can also be estimated according to the deflection amplitude of the pointer, which relies on experience.
Method 2: For analog multimeters equipped with an hFE socket for transistor testing. After identifying the base b, insert the transistor into the socket freely (the base pin must be inserted correctly), measure the hFE value, then reverse the transistor and measure again. The pin placement that yields the larger hFE reading is the correct connection.
Method 3: After determining whether the transistor is NPN or PNP and identifying its base b, set the meter to the R×10kΩ range. For an NPN transistor, when the black test lead connects to emitter e and the red test lead connects to collector c, the pointer may deflect. For a PNP transistor, when the black test lead connects to collector c and the red test lead connects to emitter e, the pointer may deflect. No deflection will occur with reversed connections. This can also be used to distinguish collector c and emitter e of the transistor.
Note that Method 3 cannot be used for high-voltage transistors. Special reminder here.
