Programming instructions

Chapter 4 Performance Verification Tests 35
• Ground Loops: Ground loops arise when the multimeter and the circuit
under test are grounded at physically different points. A typical example
of this is when a number of instruments are plugged into a power strip
in an equipment rack. If there is a potential difference between the
ground points, a current will flow through this ground loop. This
generates an unwanted voltage in series with the circuit under test. To
eliminate ground loops, ground all equipment/circuits at the same
physical point.
• Internal Temperature: The internal temperature of the 3458A
under test must be within 5°C of its temperature when last adjusted.
If the multimeter's temperature is not within 5°C first check the
multimeter's fan operation and clean the filter. Also, make sure
that you adjust the operating environment such that the ambient
temperature is at or very near 25°C. You will achieve the best
results if you maintain your environment close to 25°C. If you
choose to verify performance when the temperature is not within
5°C, you must recalculate all test limits based on the temperature
variation beyond the 5°C limitation. The published test limits were
calculated without additional temperature coefficient errors added.