The Laws of Circuit - you can learn and practice by just
Copyright. Charles Kim 2006
- Do We Need This?
- The same old and same old problem pops up
once in a while and this semester is not an exception.
The culprit is how to measure current through a resistor
using a digital Multimeter (DMM). DMM could sound like
double coated M&M chocolate candy, but its taste is
not that sweet even in the Valentines' Day. DMM can work
as a voltmeter, ammeter, and ohmmeter. Measuring the
voltage across a resistor seems to be easy to everybody.
However, seemingly easy and honest current measurement
using a DMM seems to be still uneasy an tasks in lab.
Voltage is defined as "voltage across" and
measured across a resistor. No problem. Current is
defined as "current through" and should be
measured through a resistor. Therefore, we have to cut a
branch at the end of the resistor, then we connect the
two probes of the DMM to the two ends of the cutting. Of
course in the DMM, two proper terminals must be selected
for the probes. The point in current measurement is that
current should flow through the resistor and through the
DMM (as Ammeter). In other words, the resistor and the
DMM (as Ammeter) should be in series in a branch.