Calculate The Internal Dmm Resistance R Using The Following Equation:
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Reviewed by Calculator Editorial Team
When measuring resistance with a digital multimeter (DMM), the internal resistance of the meter affects the measurement. This calculator helps you determine the internal resistance R using the standard equation for DMM measurements.
The Formula
The internal resistance R of a DMM can be calculated using the following equation:
Formula
R = (Vs - Vm) / Im
Where:
- R = Internal resistance of the DMM (Ω)
- Vs = Source voltage (V)
- Vm = Measured voltage (V)
- Im = Measured current (A)
This formula accounts for the voltage drop across the internal resistance of the meter when measuring current. The difference between the source voltage and the measured voltage is divided by the measured current to find the internal resistance.
Assumptions
- The DMM is in current measurement mode
- The source voltage is stable and constant
- The meter's internal resistance is constant for the measurement range
- No significant loading effects from the meter
Worked Example
Let's calculate the internal resistance of a DMM using the following measurements:
- Source voltage (Vs): 5.00 V
- Measured voltage (Vm): 4.95 V
- Measured current (Im): 0.01 A
Using the formula:
R = (5.00 V - 4.95 V) / 0.01 A = 0.05 V / 0.01 A = 5.0 Ω
Therefore, the internal resistance of the DMM in this example is 5.0 ohms.
FAQ
What is the internal resistance of a DMM?
The internal resistance of a DMM is the resistance that the meter presents when measuring current. It affects the accuracy of current measurements, especially at low current levels.
Why is the internal resistance important?
The internal resistance affects the accuracy of current measurements. A higher internal resistance can cause significant errors in low-current measurements.
How can I reduce the effect of internal resistance?
To minimize the effect of internal resistance, use a DMM with lower internal resistance for your measurement range, and ensure your source voltage is stable and constant.
What units are used for internal resistance?
Internal resistance is measured in ohms (Ω), the same unit used for electrical resistance.