Light; Electrostatic Interference; Magnetic Fields - Tektronix Keithley 6517B Reference Manual

Model 6517B Electrometer Reference Manual

Light

Some components, such as semiconductor junctions and MOS capacitors on semiconductor wafers,
are excellent light detectors. Consequently, these components must be tested in a light-free
environment. Many test fixtures provide adequate light protection, but others may allow enough light
penetration to affect the test results. Areas to check for light leaks include doors and door hinges,
tubing entry points, and connectors or connector panels.

Electrostatic interference

Electrostatic interference occurs when an electrically charged object is brought near an uncharged
object, inducing a charge on the previously uncharged object. Usually, effects of such electrostatic
action are not noticeable because low impedance levels allow the induced charge to dissipate
quickly. However, the high impedance levels of many 6517B measurements do not allow these
charges to decay rapidly, which may result in erroneous or unstable readings. These erroneous or
unstable readings may be caused in the following ways:
•
DC electrostatic field can cause undetected errors or noise in the reading.
•
AC electrostatic fields can cause errors by driving the input preamplifier into saturation or through
rectification that produces dc errors.
Electrostatic interference is first recognizable when hand or body movements near the experiment
cause fluctuations in the reading. Pick-up from ac fields can also be detected by observing the 6517B
preamplifier output on an oscilloscope. Line frequency signals on the output are an indication that
electrostatic interference is present.
To minimize electrostatic interference:
•
Use shielding. Possibilities include a shielded room, a shielded booth, shielding the sensitive
circuit, and using shielded cable. Refer to "Shielding and guarding" in the Model 6517B User's
Manual for detail.
•
Reduce electrostatic fields. Move power lines or other sources away from the device under test.

Magnetic fields

A magnetic field passing through a loop in a test circuit generates a magnetic EMF (voltage) that is
proportional to the strength of the field, the loop area, and the rate at which these factors
are changing.
To minimize magnetic fields:
•
Locate the test circuit as far away as possible from magnetic field sources such as motors,
transformers, and magnets.
•
Avoid moving any part of the test circuit within the magnetic field.
•
Minimize the loop area by keeping leads as short as possible and twisting them together.
6517B-901-01 Rev. E August 2022
Section 4: Measurement considerations
4-15