الرئيسية
ELECTROSTATIC VOLTMETER SYSTEMS
Many voltage measurement applications cannot be made using conventional contacting
voltmeters because they require charge transfer to the voltmeter, thus causing loading and
modification of the source voltage. For example, when measuring voltage distribution on a
dielectric surface, any measurement technique that requires charge transfer, no matter how
small, will modify or destroy the actual data. In these types of applications a new approach to
voltage measurement is needed.
An instrument that measures voltage without charge transfer is called an electrostatic
voltmeter. A primary characteristic of an electrostatic voltmeter is that it accurately measures
surface potential (voltage) on any kind of material without physical contact and therefore, no
charge transfer and loading of the voltage source can occur.
In practice, an electrostatic probe is placed close (1 mm to 5 mm) to the surface to be
measured. The electrostatic voltmeter functions to drive the potential of the probe body to the
same potential as the measured unknown. This achieves a high accuracy measurement that
is virtually insensitive to variations in probe-to-surface distances, as well as preventing arcover
between the probe and measured surface.
Scientific, industrial, or research applications for Trek electrostatic voltmeter systems include:
Research and development of electrophotographic processes
Light decay measurements of photoreceptors
High-speed measurements of photoreceptor characteristics
Contact potential measurements
Material evaluation
Charge accumulation monitoring of LCD production processes
Monitoring surface potentials in electrostatic painting processes
Measuring electrostatic potential on polymers, rubber, fabrics, and paper
Charge accumulation monitoring in clean rooms
Radiation effect studies
Measuring electrostatic potential on moving objects or surfaces
THEORY OF OPERATION
OF THE TREK ELECTROSTATIC VOLTMETER
To measure an unknown voltage on a test surface, the electrostatic probe is positioned close
to the test surface at a spacing of approximately 1 mm to 5 mm. The sensitive electrode
having a small surface area “views" the test surface through an aperture in the body of the
probe. The use of a small area electrode and aperture serves to increase the spatial
resolution of the probe to a relatively small area on the test surface. For the present
explanation, we consider the surface under test to be a large conductive surface with a uniform
potential. (Refer to block diagram below.)
The probe housing is constructed of a conductive material which serves as a reference surface
and is connected to the output of the high-voltage amplifier (A), which adjusts the voltage
applied to the probe reference surface.
The sensitive electrode is electromechanically vibrated to produce capacitive modulation
between the electrode and the test surface. If the voltage of the test surface is different than
the voltage of the reference surface (probe housing), the difference in voltage induces an AC
signal on the electrode by modulating the capacitance between the electrode and test surface.
The amplitude and phase (either 0° or 180°) of the AC signal are related to the magnitude and
polarity of the voltage difference.
The signal induced on the electrode is then fed to a preamplifier (B) in the probe.
The amplified electrode signal and the output voltage of the oscillator (M) which drives the
electromechanical modulator are connected to a phase sensitive demodulator whose output is
a DC voltage whose magnitude and polarity are related to the difference in voltage.
The signal from the phase sensitive demodulator is connected to the input of an integrating DC
high-voltage amplifier (A), the output of which is the probe housing reference potential, which
is thus driven toward the potential of the test surface.
This process continues until the probe housing has been driven to the same potential as the
potential on the test surface. At this point, the electrostatic field of the test surface will be
reduced to zero. When the electric field has been nulled, the signal induced upon the
electrode is reduced to zero, thereby reducing the demodulated signal to the integrating DC
amplifier to zero. Thus the high-voltage amplifier (A) output and the probe housing are
maintained at the potential of the test surface.
The output of the high-voltage amplifier (A) is divided down to low voltage to drive buffer
amplifier (C) for accurate monitoring and display of the measured electrostatic potential on the
test surface.
TREK ELECTROSTATIC VOLTMETER ADVANTAGES
NONCONTACTING MEASUREMENT:
Trek Electrostatic Voltmeters accomplish voltage measurement without touching the surface
under test. This technique ensures no charge transfer from the surface and therefore no
modification of the measured voltage. This technique also permits measurements of voltages on moving surfaces.
LARGE SIGNAL STRENGTH:
The patented design of Trek probes gives a large signal output to reduce noise and drift, and
to maintain performance at wide probe-to-surface distances. In Trek probes, the electrode is
located on a vibrating reed. This places the electrode in motion in the aperture, close to the surface for maximum signal output.
INSENSITIVITY TO PROBE-TO-SURFACE SPACING:
The field-nulling technique for noncontacting measurement achieves DC stability and high
accuracy even if the probe-to-surface spacing changes. This permits measurements on either
stationary or moving surfaces without the need to establish a fixed spacing to maintain
accuracy. In addition, arcing between the probe and test surface is avoided, even at very
close spacings, due to this field-nulling technique.
Many voltage measurement applications cannot be made using conventional contacting
voltmeters because they require charge transfer to the voltmeter, thus causing loading and
modification of the source voltage. For example, when measuring voltage distribution on a
dielectric surface, any measurement technique that requires charge transfer, no matter how
small, will modify or destroy the actual data. In these types of applications a new approach to
voltage measurement is needed.
An instrument that measures voltage without charge transfer is called an electrostatic
voltmeter. A primary characteristic of an electrostatic voltmeter is that it accurately measures
surface potential (voltage) on any kind of material without physical contact and therefore, no
charge transfer and loading of the voltage source can occur.
In practice, an electrostatic probe is placed close (1 mm to 5 mm) to the surface to be
measured. The electrostatic voltmeter functions to drive the potential of the probe body to the
same potential as the measured unknown. This achieves a high accuracy measurement that
is virtually insensitive to variations in probe-to-surface distances, as well as preventing arcover
between the probe and measured surface.
Scientific, industrial, or research applications for Trek electrostatic voltmeter systems include:
Research and development of electrophotographic processes
Light decay measurements of photoreceptors
High-speed measurements of photoreceptor characteristics
Contact potential measurements
Material evaluation
Charge accumulation monitoring of LCD production processes
Monitoring surface potentials in electrostatic painting processes
Measuring electrostatic potential on polymers, rubber, fabrics, and paper
Charge accumulation monitoring in clean rooms
Radiation effect studies
Measuring electrostatic potential on moving objects or surfaces
THEORY OF OPERATION
OF THE TREK ELECTROSTATIC VOLTMETER
To measure an unknown voltage on a test surface, the electrostatic probe is positioned close
to the test surface at a spacing of approximately 1 mm to 5 mm. The sensitive electrode
having a small surface area “views" the test surface through an aperture in the body of the
probe. The use of a small area electrode and aperture serves to increase the spatial
resolution of the probe to a relatively small area on the test surface. For the present
explanation, we consider the surface under test to be a large conductive surface with a uniform
potential. (Refer to block diagram below.)
The probe housing is constructed of a conductive material which serves as a reference surface
and is connected to the output of the high-voltage amplifier (A), which adjusts the voltage
applied to the probe reference surface.
The sensitive electrode is electromechanically vibrated to produce capacitive modulation
between the electrode and the test surface. If the voltage of the test surface is different than
the voltage of the reference surface (probe housing), the difference in voltage induces an AC
signal on the electrode by modulating the capacitance between the electrode and test surface.
The amplitude and phase (either 0° or 180°) of the AC signal are related to the magnitude and
polarity of the voltage difference.
The signal induced on the electrode is then fed to a preamplifier (B) in the probe.
The amplified electrode signal and the output voltage of the oscillator (M) which drives the
electromechanical modulator are connected to a phase sensitive demodulator whose output is
a DC voltage whose magnitude and polarity are related to the difference in voltage.
The signal from the phase sensitive demodulator is connected to the input of an integrating DC
high-voltage amplifier (A), the output of which is the probe housing reference potential, which
is thus driven toward the potential of the test surface.
This process continues until the probe housing has been driven to the same potential as the
potential on the test surface. At this point, the electrostatic field of the test surface will be
reduced to zero. When the electric field has been nulled, the signal induced upon the
electrode is reduced to zero, thereby reducing the demodulated signal to the integrating DC
amplifier to zero. Thus the high-voltage amplifier (A) output and the probe housing are
maintained at the potential of the test surface.
The output of the high-voltage amplifier (A) is divided down to low voltage to drive buffer
amplifier (C) for accurate monitoring and display of the measured electrostatic potential on the
test surface.
TREK ELECTROSTATIC VOLTMETER ADVANTAGES
NONCONTACTING MEASUREMENT:
Trek Electrostatic Voltmeters accomplish voltage measurement without touching the surface
under test. This technique ensures no charge transfer from the surface and therefore no
modification of the measured voltage. This technique also permits measurements of voltages on moving surfaces.
LARGE SIGNAL STRENGTH:
The patented design of Trek probes gives a large signal output to reduce noise and drift, and
to maintain performance at wide probe-to-surface distances. In Trek probes, the electrode is
located on a vibrating reed. This places the electrode in motion in the aperture, close to the surface for maximum signal output.
INSENSITIVITY TO PROBE-TO-SURFACE SPACING:
The field-nulling technique for noncontacting measurement achieves DC stability and high
accuracy even if the probe-to-surface spacing changes. This permits measurements on either
stationary or moving surfaces without the need to establish a fixed spacing to maintain
accuracy. In addition, arcing between the probe and test surface is avoided, even at very
close spacings, due to this field-nulling technique.
