Fluke 8588A Operator's Manual page 130

8588A/8558A
Operators Manual
EM Interference - Noisy or intense electric,
magnetic and electromagnetic effects in the
vicinity can disturb the measurement circuit.
Some typical sources are:
•
Static electric fields
•
Fluorescent lighting
•
Inadequate shielding, filtering or grounding of
power lines
• Transients from local switching
•
Induction and radiation fields of local E-M
transmitters.
•
Excessive common mode voltages between
the source and load.
These disturbances can be magnified by the
capacitance of your hand. Electrical interference
has the greatest effect in high-impedance circuits.
Separation of leads and creation of loops in the
circuit can intensify the disturbances.
Test Lead Resistance can drop significant
voltages between the source and load, especially
at high load currents.
Lead Insulation Leakage can cause significant
errors in measurement circuits at high voltages
and high resistances.
Some insulating materials suffer greater losses
than others, for example. PVC has more leakage
than PTFE.
126
Table 25. Guidelines to Avoid Errors (cont.)
Sources of Inaccuracy Avoiding or Minimizing Inaccuracy
Choose as interference-free a site as possible (a
screened cage may be necessary if interference
is heavy or circuit impedance is high). Suppress
as many sources as possible.
•
Always keep interconnecting leads as short
as possible, especially unshielded lengths.
• Run leads together as twisted pairs in a
common shield to reduce loop pick-up area,
but beware of leakage problems and
excessive capacitance.
•
Where both source and load are floating,
connect LO to ground at the source to
reduce common mode voltages.
• If an external measurement ground
connection has been made, select External
Guarding at the Product in Voltage and
Current functions and deselect External
Guarding in Ohms and PRT functions.
•
When connecting to a multifunction calibrator
such as the Fluke 5730A or 5522A, follow
the Product guarding and grounding advice
and deselect External Guard at the Product.
Keep all leads as short as possible.
•
Use conductors with a good margin of
current-carrying capacity.
•
Use External Guard or 4-wire connections
where necessary.
Choose low loss insulated leads - PTFE is
preferred to PVC. When running leads together in
shielded pairs, avoid large voltages between
leads in the same screen, especially if using PVC
insulation.