Three Critical Precautions and Operating Principles for Measuring Variable Resistors Using a Multimeter
There are many issues that need to be paid attention to when using adjustable resistor products, such as when using a multimeter to measure adjustable resistors. Here are three precautions for measuring adjustable resistance with a multimeter, as follows:
Note 1: The measuring range should be determined based on the measured resistance value, so that the pointer indicates the middle section of the scale line for easy observation;
Note 2: Do not touch the two ends of the resistor or the metal part of the probe when inspecting the heating element resistor. Otherwise, it may cause testing errors;
Note 3: After confirming the range of the resistance range through inspection, we need to perform zero adjustment. The method is to short-circuit the two probes (directly touch each other), adjust the "zero adjustment" device so that the pointer accurately points to the "0" on the Ω scale line, and then measure the resistance value of the resistor.
Tag: multimeter
Three precautions for measuring adjustable resistance with a multimeter
Principle of measuring capacitance with a multimeter
Use a multimeter to measure the capacitance value based on the current variation over time during capacitor charging, and use a stopwatch to measure the time from the moment the capacitor is turned on to the selected end point to calculate the capacitance value. Firstly, set the multimeter to the resistance range and adjust the mechanical and zero settings. Then connect the capacitor and start timing until it reaches a point close to ∞, at which point the timing will end.
i=i0e-t/τ(τ=RC)
C=t/{r0 × [- ln (i final/i0)]}...... ①
C=- t/{r0 × ln [r0/(r0+r final)... ②
Where t: Time from the moment the capacitor is connected to the selected end point (in seconds)
R0: Multiply the center resistance value of the selected resistance range of the multimeter by the multiplier of that range (e.g. R × 10 range, multiply the center resistance value by 10 to obtain r0) Unit: Ω
R-terminal: The resistance value at the selected end point during capacitor charging. (Unit: Ω)
End: The multimeter selects the full current value of the resistance range, which is the open circuit voltage value E of the resistance range divided by the center resistance value multiplied by the multiplier of that range. (Unit: A)
I0: End current point of capacitor charging [i0=E/(r0+r-terminal] (unit: A)]
Method for selecting the endpoint:
The capacitance value can be calculated using equation ② with a digital resistance scale line close to ∞; Or use the first grid point of the voltage and current range as the ending point, and calculate using equation ① (iTerminal/i0=1/5. A multimeter usually has 50 grids)
