Diagnostic Fundamentals with a DMM
A Digital Multimeter (DMM) is the primary diagnostic tool for any engineer. Understanding its limitations, such as burden voltage and input impedance, is crucial.
A typical DMM has a 10MΩ input impedance on voltage ranges. While usually negligible, measuring a high-impedance node (like a 1MΩ voltage divider) will skew the reading due to the parallel resistance of the meter.
Key Specifications Data
| Measurement | Meter Connection | Circuit State |
|---|---|---|
| Voltage | Parallel | Powered On |
| Current | Series | Powered On |
| Resistance/Continuity | Parallel | Powered Off (Discharged!) |
Frequently Asked Questions
What is burden voltage?
The voltage drop across the multimeter itself when measuring current. It can cause a circuit operating at low voltages to fail when the meter is inserted.
Why did my meter blow a fuse on the mA setting?
You likely tried to measure voltage while the probes were plugged into the current jacks, effectively shorting out the power supply.
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