IEC 61757-7-3:2024

IEC 61757-7-3 ®
Edition 1.0 2024-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Fibre optic sensors –
Part 7-3: Voltage measurement – Polarimetric method

Capteurs fibroniques –
Partie 7-3: Mesure de tension – Méthode polarimétrique
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IEC 61757-7-3 ®
Edition 1.0 2024-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Fibre optic sensors –
Part 7-3: Voltage measurement – Polarimetric method

Capteurs fibroniques –
Partie 7-3: Mesure de tension – Méthode polarimétrique

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 33.180.99  ISBN 978-2-8322-8756-9

– 2 – IEC 61757-7-3:2024 © IEC 2024
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Components of optical voltage sensor using polarimetric method . 9
4.1 General description . 9
4.2 Classification of Pockels cells . 10
5 Characteristic tests . 11
5.1 General information . 11
5.2 Input-to-output characteristics . 11
5.2.1 General . 11
5.2.2 Test methods . 12
5.2.3 Test procedure . 14
5.2.4 Evaluation . 16
5.3 Warm-up time . 17
5.3.1 General . 17
5.3.2 Test method . 17
5.3.3 Evaluation . 17
5.4 Voltage conditions for obtaining characteristic parameters . 17
5.5 Input parameter dependency . 18
5.5.1 Frequency characteristics . 18
5.5.2 Transient characteristics . 19
5.6 External environment dependency . 21
5.6.1 Test of the steady state temperature characteristics . 21
5.6.2 Test of the transient temperature characteristics . 23
5.6.3 Shock and vibration test . 26
Annex A (informative) Principle of optical voltage sensor . 27
A.1 Outline . 27
A.2 Pockels effect . 27
A.3 Voltage detection method . 29
A.3.1 General . 29
A.3.2 Examples of voltage detection method . 30
Annex B (informative) Features of optical voltage sensor technology . 32
Annex C (informative) Design considerations . 33
C.1 General information . 33
C.2 Performance restricting factors . 33
C.3 Procedure for determining the specifications of the equipment . 34
Annex D (informative) Measurement parameter performance table . 36
D.1 General . 36
D.2 I/O characteristics . 36
D.3 Frequency characteristics . 37
D.4 Transient characteristics . 38
D.5 Steady state temperature characteristics . 39
D.6 Transient temperature characteristics . 40
D.7 Shock test . 41

Bibliography . 42

Figure 1 – Measurement system using optical voltage sensor . 10
Figure 2 – I/O characteristics of a fibre optic voltage sensor . 12
Figure 3 – Measurement setup for the waveform comparison method . 13
Figure 4 – Measurement setup for the AC bridge method . 14
Figure 5 – Transient characteristics of sensors for AC measurements . 20
Figure 6 – Transient characteristics of sensors for AC/DC measurements. 21
Figure 7 – Configuration example for evaluating the steady temperature and transient
temperature characteristics of the sensor part . 22
Figure 8 – Example of a temperature profile. 23
Figure 9 – Birefringence change during temperature change. 24
Figure 10 – Example of temperature program . 25
Figure A.1 – Pockels effect . 28
Figure A.2 – Configuration of a voltage detection system using the Pockels effect . 29
Figure A.3 – Basic configuration of an optical voltage sensor using the intensity
modulation method . 30
Figure A.4 – Basic configuration of an optical voltage sensor using the interferometric
method . 31
Figure D.1 – Example of the transient characteristic . 38
Figure D.2 – Example of the temperature characteristics at voltage 0 . 39
Figure D.3 – Example of the temperature characteristics at rated voltage . 39
Figure D.4 – Example of the transient temperature characteristics at input voltage 0 . 40
Figure D.5 – Example of the transient temperature characteristics at rated voltage . 40
Figure D.6 – Example of the shock test at voltage 0 . 41
Figure D.7 – Example of the shock test at rated voltage . 41

Table 1 – List of parameters to be obtained . 11
Table 2 – Test methods . 13
Table 3 – Voltage conditions for obtaining characteristic parameters . 18
Table A.1 – Direction of electric field with sensitivity . 29
Table D.1 – I/O characteristics . 36
Table D.2 – Frequency characteristics . 37

– 4 – IEC 61757-7-3:2024 © IEC 2024
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
FIBRE OPTIC SENSORS –
Part 7-3: Voltage measurement – Polarimetric method

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
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preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with
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Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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9) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
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shall not be held responsible for identifying any or all such patent rights.
IEC 61757-7-3 has been prepared by subcommittee SC 86C: Fibre optic systems and active
devices, of IEC technical committee TC 86: Fibre optics. It is an International Standard.
The text of this International Standard is based on the following documents:
Draft Report on voting
86C/1873/CDV 86C/1893/RVC
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.

This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
A list of all parts in the IEC 61757 series, published under the general title Fibre optic sensors,
can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn, or
• revised.
– 6 – IEC 61757-7-3:2024 © IEC 2024
INTRODUCTION
This document is part of the IEC 61757 series, which is dedicated to fibre optic sensors. Generic
specifications for fibre optic sensors are defined in IEC 61757.
The individual parts of the IEC 61757 series are numbered as IEC 61757-M-T, where M denotes
the measure and T the technology of the fibre optic sensor. The IEC 61757-7-T series is
concerned with voltage measurements.
Voltage measuring techniques are essential for controlling and diagnosing apparatus that
support industry and society. Optical voltage sensors based on electro-optic effects have been
developed to serve as voltage measuring devices. These sensors enable advanced voltage
measurements without encountering the issues related to conventional electrical voltage
sensors. Hence, they have been applied in various fields including power systems.
Given the expected potential of this new fibre optic voltage sensing technology, several kinds
of optical voltage sensors covering a wide range of applications have been developed by
various manufacturers. The design of these voltage sensors depends on the specific application,
which determines the target voltage to be measured, the configuration of the sensor, the signal
processing method, and the installation method. When developing a new optical voltage sensor,
the sensor performance and characteristics have to be specified and evaluated.
To facilitate the use of fibre optic voltage sensors, it is important to define terms that
characterize the performance and functionality of these sensors. It is also important to clearly
specify how these specifications can be evaluated. Clearly defined terms and evaluation
procedures help to develop more efficient sensors and to smoothly transfer this new sensor
technology from the suppliers to the users. This document defines a set of methods for
evaluating the performance and characteristics of fibre optic voltage sensors. However, this
document does not quantify any performance targets, because these depend on the specific
application of the sensor. It is nevertheless expected that this document helps to define specific
quantitative targets for the sensor performance when a fibre optic voltage sensor is developed
for a given practical application.
This document is based on the standard OITDA FS 02 [1] published by the Optoelectronic
Industry and Technology Development Association (OITDA). All the figures and tables in this
document are identical to those in OITDA FS 02 except for the translation from Japanese to
English.
___________
Numbers in square brackets refer to the Bibliography.

FIBRE OPTIC SENSORS –
Part 7-3: Voltage measurement – Polarimetric method

1 Scope
This part of IEC 61757 defines the terminology, structure, and performance characteristics of
fibre optic voltage sensors using a polarimetric measurement method. The document specifies
test methods and procedures for measuring key performance parameters of these sensors. It
addresses only the voltage sensing element and not the additional devices that are unique to
each application.
The document does not specify the required performance values of optical polarimetric fibre
optic voltage sensors, because these specifications depend on the designated application of
the sensor and are typically defined by the user of the sensor. The required performance values
are usually defined when designing a sensor for a specific application.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 61757, Fibre optic sensors – Generic specification
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 61757 and the
following apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.1
electro-optic effect
change in the optical characteristics of a material under the influence of an electric field
Note 1 to entry: Pockels and Kerr effects are examples of electro-optic effects.
Note 2 to entry: Electro-optic is often erroneously used as a synonym for opto-electronic.
Note 3 to entry: The most common effect results in a change in refractive index.
[SOURCE: IEC 60050-731:1991, 731-01-42]
3.2
intensity modulation method
method of converting birefringence information into light intensity by passing light through a
wave plate, a Pockels cell, and a polarization separation element in this order, and creating an
optical signal corresponding to the measured voltage

– 8 – IEC 61757-7-3:2024 © IEC 2024
3.3
interferometric method
method in which two orthogonal linearly polarized light components are passed through a
Pockels cell and then converted into the same polarization state, so that they interfere with
each other and are converted into light intensity to create an optical signal corresponding to the
measured voltage
3.4
maximum measurable frequency
highest frequency of voltage variations that can be measured by an optical voltage sensor
3.5
maximum measurable voltage
largest voltage that can be measured by an optical voltage sensor
3.6
minimum measurable frequency
lowest frequency of voltage variations that can be measured by an optical voltage sensor
3.7
operating temperature range
range of temperature within which an optical voltage sensor shall satisfy the defined
performance
3.8
optical activity
property of rotating the plane of polarization
3.9
optical part
part consisting of lens, prism, mirror, and optical element, like a phase modulator, in an optical
voltage sensor
Note 1 to entry: While the term "sensor part" focuses on the component position (see Clause 4), the term "optical
part" focuses on the component materials.
3.10
optical voltage sensor
component, module, subassembly, assembly, or device that can detect voltage using the
Pockels effect
Note 1 to entry: The optical voltage sensor consists of a sensor unit, an optical transmission unit, and a signal
processing unit (see Clause 4).
3.11
photo-conductivity
photo-electric effect characterized by a variation of electrical conductivity
[SOURCE: IEC 60050-731:1991, 731-01-62]
3.12
piezoelectric effect
generation of an electric field in response to an applied mechanical stress or generation of a
stress in response to an applied electric field
Note 1 to entry: A more complete definition is given in IEC 60050-121:1998, 121-12-86.

3.13
Pockels coefficient
coefficient that indicates the difference in the refractive indexes of the birefringence that occurs
in response to the electric field applied to the substance
Note 1 to entry: See Annex A for details.
3.14
Pockels effect
electro-optic effect in which an applied electric field makes an optically isotropic substance
birefringent, the difference of refractive indexes being proportional to the magnitude of the
electric field strength
[SOURCE: IEC 60050-121:1998, 121-12-94]
3.15
rated voltage
rated value of the voltage assigned by the manufacturer to a component, device, or equipment
and to which operation and performance characteristics are referred
3.16
required specifications
list of specifications an optical voltage sensor shall satisfy
3.17
transient characteristics
phenomena of changing the voltage value that is output from an optical voltage sensor when
the voltage to be measured deviates from the defined voltage value over a short period of time
3.18
voltage divider
device comprising resistors, inductors, capacitors, or a combination of these components such
that, between two points of the device, a desired fraction of the voltage applied to the device
can be obtained
Note 1 to entry: A voltage divider acquires part of the voltage applied to the entire device between two points of the
device.
[SOURCE: IEC 60050-312:2001, 312-02-32, modified – Removed "transformer(s)" from
definition and added Note 1 to entry]
3.19
warm-up time
duration between the instant after which the power supply is energized and the instant when
the measuring instrument may be used, as specified by the manufacturer
[SOURCE: IEC 60050-311:2001, 311-03-18]
4 Components of optical voltage sensor using polarimetric method
4.1 General description
Figure 1 shows a schematic diagram of the various elements of which an optical voltage sensor
is composed. In this document, the optical voltage sensor is divided into three parts: a sensor
part, an optical transmission part, and a signal processing part. Each of these parts can be
exposed to different physical environments.

– 10 – IEC 61757-7-3:2024 © IEC 2024
The sensor part of the optical voltage sensor contains a Pockels cell that is connected to two
electric conductors whose voltage difference is to be measured. It is connected via two optical
fibres to the signal processing part, which calculates the voltage measured by the sensor part.
While the sensor part is placed adjacent to the electric conductors, the signal processing part
is generally placed in a remote location and thus exposed to a different environment than the
sensor part.
Source: OITDA FS 02 [1], reproduced with the permission of the Optoelectronic Industry and Technology
Development Association (OITDA).
Figure 1 – Measurement system using optical voltage sensor
The optical fibres that connect the sensor part to the signal processing part is called the optical
transmission part.
The light source for generating the optical signal transmitted to the sensor part via optical fibre
is typically included in the signal processing part. Likewise, the light detector for receiving the
optical signal transmitted from the sensor part via optical fibre is included in the signal
processing part, which also contains the power supplies.
More details on the specific functions of each part can be found in Annex A.
NOTE The sensor part can include elements for controlling polarization and phase of the optical signal, and a
voltage divider for adjusting the voltage applied to the Pockels cell. The signal processing part can have elements
for controlling polarization and phase of the optical signal, in addition to the light source, power supply, and light
detector.
A component, module, subassembly, assembly, or device that comprises a sensor part with a
Pockels cell, an optical transmission part, and a signal processing part is called an optical
voltage sensor.
See Annex B for more details on the specific features of polarimetric fibre optic voltage sensors
and Annex C for design considerations and performance specifications.
4.2 Classification of Pockels cells
Pockels cells can be divided into two classes. Some Pockels cells have longitudinal modulation
elements in which the light transmission direction and the voltage application direction are
parallel, whereas other Pockels cells have transverse modulation elements in which the light
transmission direction and the voltage application direction are orthogonal to each other.
More details on the operation of Pockels cells can be found in Annex A.

5 Characteristic tests
5.1 General information
Clause 5 specifies a characteristic test method for the optical voltage sensor.
The input-to-output (I/O) characteristics are described in 5.2 and are the basis of the test.
Subclause 5.3 describes the warm-up time, which is not considered in conventional voltage
sensors. Subclause 5.5 defines the input parameter dependency for each test method and 5.6
the external environment dependency.
Subclause 5.4 describes the voltage conditions for obtaining characteristic parameters. The
parameters to be obtained are listed in Table 1, which specifies for each parameter whether
tests are required or optional. The measurement results are summarized in an inspection report
(see Annex D) and shown to the user.
Table 1 – List of parameters to be obtained
No. Parameters Required or optional
1 I/O characteristics Required
2 Warm-up time Required
3 Parameter dependency Input parameter Frequency characteristic Required for type test
dependency
Transient characteristic Required for type test
External environment Steady state temperature Required for type test
dependency characteristic
Optional for routine test for
outdoor use sensors
Transient temperature Required for type test
characteristic
Optional for routine test for
outdoor use sensor
Shock and vibration Optional
5.2 Input-to-output characteristics
5.2.1 General
The I/O characteristics are the most basic performance parameters of optical voltage sensors.
Figure 2 shows the I/O characteristics of a typical fibre optic voltage sensor. Ideally, the voltage
to be measured is the same as the output voltage reported by the sensor. In practice, the output
voltage can deviate from the voltage to be measured, thus resulting in a measurement error.
These errors are caused by the following three factors:
a) noise,
b) sensitivity change,
c) non-linearity.
There are two types of noise. In some cases, the noise is correlated with the voltage to be
measured, and in other cases it is not. Therefore, these two types of noise shall be
characterized separately. DC offsets in the output voltage should be distinguished from noise.
Sensitivity change is a variation in the proportionality between reported output voltage and the
voltage to be measured.
Non-linearity is the phenomenon that the sensitivity of the voltage sensor changes as a function
of voltage to be measured, so that the relationship between the reported output voltage and the
voltage to be measured deviates from a straight line.

– 12 – IEC 61757-7-3:2024 © IEC 2024
Figure 2 illustrates the effects of noise, sensitivity change, and non-linearity on the reported
output voltage.
Source: OITDA FS 02 [1], reproduced with the permission of OITDA.
Figure 2 – I/O characteristics of a fibre optic voltage sensor
The errors resulting from noise, sensitivity change, and nonlinearities, should be accounted for
separately because they are affected differently by environmental changes, such as
temperature changes (see 5.6.1) and vibration (see 5.6.3). In general, the output voltage of a
sensor saturates when the voltage to be measured exceeds a certain value, which is marked
as maximum measurable voltage in Figure 2. The manufacturer of an optical voltage sensor
specifies the maximum measurable voltage below the value at which the output voltage no
longer increases with input voltage, and defines said value in the specifications. The
manufacturer also determines the rated voltage (see Figure 2) as the largest voltage that can
be measured without being affected by saturation, and defines it in the sensor specifications.
Due to the impacts of noise, sensitivity change, and non-linearity, the actual sensor output
voltage varies between the black solid curve and the black dashed curve in Figure 2.
5.2.2 Test methods
5.2.2.1 General
Table 2 provides a list of test methods for characterizing measurement errors caused by noise,
sensitivity change, and non-linearity of the optical voltage sensor. In general, the tests shall be
performed by a waveform comparison method, using a waveform recording device, like an
oscilloscope. However, when testing non-linearities of 1 % or less with an analogue output, and
if sufficient accuracy is not achieved with a waveform recording device, the bridge method can
be applied in addition to the waveform comparison method. When a photo-conductive Pockels
cell is used (see 3.11), the effects of ambient light should be considered, like the lighting present
in the use environment. All equipment used shall be calibrated before the test according to the
manufacturer’s instructions.
Table 2 – Test methods
Items In the case of In the case of
digital output analogue output
General measurement General measurement High accuracy
measurement
Noise Waveform comparison Waveform comparison Not applicable
method method
Sensitivity change Waveform comparison Waveform comparison Bridge method
method method
Non-linearity Waveform comparison Waveform comparison Bridge method
method method
Subclause 5.2.2.2 describes an exemplary test configuration for the waveform comparison
method, and 5.2.2.3 describes an exemplary test configuration for the AC bridge method.
5.2.2.2 Waveform comparison method
Figure 3 shows an example of the test configuration used for the waveform comparison method.
A voltage transformer or a voltage divider can be used to generate a voltage standard for
comparison. Figure 3 shows the example of a voltage transformer. The voltage measured
directly at the output of the voltage transformer and the voltage measured by the optical voltage
sensor are recorded in a waveform recording device, such as an oscilloscope or a data logger.
The voltage transformer or voltage divider and the waveform recording device should have
sufficiently accurate response in the tested frequency band. The measured waveforms shall be
recorded as digital data in order to calculate errors and phase differences as described in 5.2.4.
To avoid aliasing errors in the digitization, an anti-alias filter that attenuates signals other than
the measuring frequency band of the waveform recording device shall be installed before the
waveform recording device.
Source: OITDA FS 02 [1], reproduced with the permission of OITDA.
Figure 3 – Measurement setup for the waveform comparison method

– 14 – IEC 61757-7-3:2024 © IEC 2024
5.2.2.3 AC bridge method
If the accuracy of the waveform recording device is insufficient, a bridge method should be used
concurrently. Figure 4 shows an example of a test configuration for the case of an optical
voltage sensor with analogue voltage output. A voltage transformer or a voltage divider can be
used as a voltage standard for comparison. In Figure 4, the bridge includes adjustable resistors
and capacitors on the voltage sensor side to balance the impedance of the voltage transformer
side. Sensitivity changes of the optical voltage sensor are detected by a voltmeter, which
measures the deviation of the bridge circuit from the equilibrium point. Only sensitivity changes
and non-linearities, as described in 5.2.1, can be measured with this method. The noise shall
be characterized with the waveform comparison method described in 5.2.2.2.

Source: OITDA FS 02 [1], reproduced with the permission of OITDA.
Figure 4 – Measurement setup for the AC bridge method
5.2.3 Test procedure
5.2.3.1 Sensors for AC or AC/DC measurements
The waveform comparison method characterizes the noise, sensitivity change, and non-linearity
of the sensor, as described in 5.2.1, by comparing the waveform obtained from the voltage
standard with the output waveform of the optical voltage sensor. This comparison is conducted
at several levels of the voltage to be measured, ranging from zero to the maximum measurable
voltage. This comparison is conducted at the voltage levels listed below.
a) At zero voltage:
Noise measurement only. The noise intensity should be characterized as a function of
frequency using a suitable frequency analysis tool (e.g. fast Fourier transform), preferably
the frequency analysis function of an oscilloscope. It is highly likely that the frequency
component of the voltage to be measured and its harmonics adversely affect the system.

b) At the noise equivalent voltage and at approximately twice the noise equivalent voltage:
1) Separate the noise into a component that is correlated with the voltage to be measured
and one that is not correlated with the voltage.
2) Noise that does not correlate with the measured voltage is reduced by averaging a large
number of waveforms obtained from the waveform recording device (e.g. oscilloscope).
3) Noise that correlates with the measured voltage is not affected by averaging the
waveforms obtained from the waveform recording device.
4) Record the waveforms obtained from the waveform recording device with and without
averaging.
c) At several voltages between the voltage that are approximately twice the noise equivalent
voltage and the rated voltage.
This allows accurate measurement of sensitivity changes.
d) At several voltages between the rated voltage and the maximum measurable voltage.
This allows accurate measurement of non-linearities.
The waveforms acquired by the waveform recording device are approximated by sinusoids,
using the least squares method to determine the amplitude and phase of the recorded waveform.
The function used for the sinusoidal approximation of the waveform obtained from the voltage
standard is shown in Formula (1), and the function used for the sinusoidal approximation of the
waveform of the optical voltage sensor output is shown in Formula (2).
ν V sin ωt++θ V
( ) (1)
I I I DCI
where
v is the voltage to be measured, obtained from the voltage standard,
I
V is the amplitude of the AC component of the voltage to be measured,
I
V is the DC component of the voltage to be measured,
DCI
ω is the angular frequency of the voltage to be measured,
θ is the phase of the voltage to be measured.
I
ν V sin ωt++θ V
(2)
( )
O O O DCO
where
v is the optical voltage sensor output,
O
V is the amplitude of the AC component of the optical voltage sensor output,
O
V is the DC component of the optical voltage sensor output,
DCO
ω is the angular frequency of the voltage to be measured (which is equal to the angular
frequency of optical voltage sensor),
θ is the phase of the optical voltage sensor output.
O
=
=
– 16 – IEC 61757-7-3:2024 © IEC 2024
5.2.3.2 Sensors for DC measurement
To characterize the noise, sensitivity change and non-linearity, as described in 5.2.1, the
waveform of the standard for comparison shall be compared with the output waveform of the
optical voltage sensor at several levels of the voltage to be measured. This comparison is
conducted at the voltage levels listed below.
a) At zero voltage to be measured.
Determine the offset in the optical voltage sensor output from the average value of the
waveform obtained from the optical voltage sensor output at zero voltage.
b) At several voltages between the voltage that is approximately twice the noise equivalent
voltage and the rated voltage.
This allows accurate measurement of sensitivity changes.
c) At several voltages between the rated voltage and the maximum measurable voltage.
This allows accurate measurement of non-linearities.
5.2.4 Evaluation
5.2.4.1 Sensors for AC or AC/DC measurement
The input/output characteristic test shall be performed by comparing the error, phase difference,
and noise of the optical voltage sensor output with the required specifications.
a) Error
Errors should be expressed as the full-scale error defined in Formula (3). Other notation
methods may be used as necessary.
VV−
OI
ε =
(3)
FS
V
FS
where
ε is the full-scale error,
FS
V is the amplitude of the voltage to be measured,
I
V is the amplitude of the optical voltage sensor output,
O
V is the maximum measurable voltage.
FS
b) Phase difference
The phase differ
...