HT Italia HT7052 User manual

Copyright HT ITALIA 2013 Release EN 2.00 - 02/01/2013
ENGLISH
User manual

HT7052
EN - 1
Table of Content:
1PRECAUTIONS AND SAFETY MEASURES.............................................................................. 2
1.1Preliminary instructions........................................................................................................................ 2
1.2During use............................................................................................................................................ 3
1.3After use............................................................................................................................................... 3
1.4Definition of measurement (overvoltage) category .............................................................................. 3
2GENERAL DESCRIPTION.......................................................................................................... 4
2.1Instrument features .............................................................................................................................. 4
3PREPARATION FOR USE.......................................................................................................... 5
3.1Initial inspections.................................................................................................................................. 5
3.2Instrument power supply...................................................................................................................... 5
3.3Calibration ............................................................................................................................................ 5
3.4Storage................................................................................................................................................. 5
4DESCRIPTION OF PARTS.......................................................................................................... 6
4.1Instrument description.......................................................................................................................... 6
4.2Description of test leads....................................................................................................................... 7
5INITIAL OPERATIONS................................................................................................................ 8
5.1Switching on the instrument................................................................................................................. 8
5.1.1Mains powered instrument operation................................................................................................ 8
5.1.2Backlight operation............................................................................................................................ 8
5.1.3Autocalibration................................................................................................................................... 8
5.2Configuration and Setup of systems parameters................................................................................. 9
6HOW TO PERFORM THE MEASUREMENTS.......................................................................... 10
6.1Theory of insulation resistance measurement ................................................................................... 10
6.1.1Time dependence test – Diagnostic test......................................................................................... 12
6.1.2Withstanding voltage test................................................................................................................ 15
6.2Guard terminal.................................................................................................................................... 16
6.3Use of internal filters........................................................................................................................... 17
6.3.1The purpose of filtering.................................................................................................................... 17
6.4Voltage measurement........................................................................................................................ 18
6.5Insulation resistance measurement ................................................................................................... 19
6.5.1Setting of parameters...................................................................................................................... 19
6.5.2Perform the measurement............................................................................................................... 20
6.6Diagnostic test.................................................................................................................................... 22
6.6.1Setting of parameters...................................................................................................................... 22
6.6.2Perform the measurement............................................................................................................... 23
6.7Insulation resistance with step voltage test........................................................................................ 25
6.7.1Setting of parameters...................................................................................................................... 25
6.7.2Perform the measurement............................................................................................................... 26
6.8Withstanding voltage test................................................................................................................... 28
6.8.1Setting of parameters...................................................................................................................... 28
6.8.2Perform the measurement............................................................................................................... 29
7MANAGEMENT OF MEMORY DATA....................................................................................... 30
7.1Saving, recall and clear measurement results................................................................................... 30
8CONNECTION OF THE INSTRUMENT TO PC ........................................................................ 31
8.1Installation of software and initial configurations (Win XP)................................................................ 31
9MAINTENANCE......................................................................................................................... 33
9.1General information............................................................................................................................ 33
9.2Replacement and charging batteries ................................................................................................. 33
9.3Cleaning the instrument ..................................................................................................................... 33
9.4End of life............................................................................................................................................ 33
10TECHNICAL SPECIFICATIONS ............................................................................................... 34
10.1Safety standards ................................................................................................................................ 35
10.2General characteristics....................................................................................................................... 36
10.3Environment....................................................................................................................................... 36
10.4Accessories........................................................................................................................................ 36
11SERVICE ................................................................................................................................... 37
11.1Warranty conditions............................................................................................................................ 37
11.2Service................................................................................................................................................ 37

HT7052
EN - 2
1 PRECAUTIONS AND SAFETY MEASURES
The instrument has been designed in compliance with standards IEC/EN61557-1 and
IEC/EN61010-1 regarding electronic measuring instruments
CAUTION
For the operator’s safety and to prevent damaging the instrument, follow the
procedures described in this manual and carefully read all notes preceded by
the symbol
Before and during measurements, carefully observe the following instructions:
Do not perform any measurement in humid environments, in the presence of gas or
explosive or inflammable material or in dusty areas
Even when no measurements are being performed, avoid any contact with the circuit
being tested, with exposed metal parts, with unused measuring leads or circuits, etc
Do not perform any measurement when anomalies are found in the instrument, such as
deformations, breaks, substance leaks, no display view, etc
Pay special attention when measuring voltages above 25V in special environments
(building yards, swimming pools, etc.) and 50V in ordinary environments, as there is the
danger of electric shocks
In this manual and on the instrument, the following symbols are used:
WARNING: Observe the instructions reported in the manual. An improper use
could damage the instrument and lead to dangerous situations for the operator
DC voltage or current
Dangerous voltages: risk of electric shocks
Instrument with double insulation
1.1 PRELIMINARY INSTRUCTIONS
This instrument has been designed for use in an environment with pollution level 2
It may also be used to test industrial electrical systems up to CAT IV 600V to earth with
maximum voltage 600V between inputs
Follow the usual safety rules to protect the operator from dangerous currents and
protect the instrument against improper use
Never use the instrument resting on the floor, it must be placed over flat horizontal
surfaces
Only the accessories supplied with the instrument guarantee safety standards. They
must be in good conditions and replaced, if necessary, with identical models
Do not measure systems exceeding the current and voltage limit values specified
Do not perform measurements in environmental conditions not within the limit values
indicated in this manual
Before connecting the probes to the circuit to be tested, check that the correct function
is selected

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EN - 3
1.2 DURING USE
Carefully read the following recommendations and instructions:
CAUTION
Failure to observe the warnings and/or instructions may damage the
instrument and/or its components or generate a danger for the operator. If,
during use, the low battery symbol appears on the display, insert the supply
cable into the Europlug socket to start battery recharge. During battery
recharge, it is possible to perform measurements
Before selecting a new function, disconnect the measuring probes from the circuit
When the instrument is connected to the circuit being tested, never touch any unused
lead
Avoid measuring resistance with external voltages. Even if the instrument is protected,
as an excess voltage may cause instrument malfunctions
In case of a capacitive test object (long tested cable etc.), automatic discharge of the
object may not be done immediately after finishing the measurement – “Please wait,
discharging” message will be displayed
Handling with capacitive loads note that 40nF charged to 1kV or 5nF charged to 10 kV
are hazardous live
1.3 AFTER USE
When measurements are completed, turn off the instrument by pressing the ON/OFF key
1.4 DEFINITION OF MEASUREMENT (OVERVOLTAGE) CATEGORY
Standard "IEC/EN61010-1: Safety requirements for electrical equipment for measurement,
control and laboratory use, Part 1: General requirements", defines what is intended for
measurement category, commonly known as overvoltage category. In § 6.7.4: Measuring
circuits, it reads:
Circuits are divided into the following measurement categories:
Measurement category IV is for measurements performed at the source of a low-
voltage installation
Examples are electric counters and measurements on primary devices protecting
against overcurrents and on ripple adjusting units
Measurement category III is for measurements performed on installations inside
buildings
Examples are measurements performed on distribution boards, circuit breakers, wiring
harnesses, including cables, bars, junction boxes, switches, sockets of fixed
installations and appliances designed for industrial use and other equipment, e.g.
stationary motors connected to fixed systems
Measurement category II is for measurements performed on circuits directly
connected to the low-voltage installation
Examples are measurements performed on household appliances, portable tools and
similar equipment
Measurement category I is for measurements performed on circuits not directly
connected to the MAINS
Examples are measurements performed on circuits not derived from the MAINS and on
circuits derived from the MAINS provided with a special (internal) protection. In this
latter case, the stress caused by the transients is variable; therefore, (OMISSIS) it is
necessary that the user knows the appliance’s resistance to transients

HT7052
EN - 4
2 GENERAL DESCRIPTION
The instrument HT7052 You purchased, if used in compliance with the indications given in
this manual, guarantees accurate and reliable measurements and the utmost safety
thanks to a development of new conception which ensures double insulation and,
consequently, compliance with the requirements of overvoltage category IV
2.1 INSTRUMENT FEATURES
High insulation resistance measurement up to 10 T
Programmable test voltage from 500V up to 10 kV, step 25 V
R(t) Graphs
Programmable timer (1s up to 30 min)
Automatic discharge of test object after completion of measurement
Capacitance measurement
Insulation resistance measurement with step-up voltage test
Five discrete test voltages proportionately set within preset test voltage range
Programmable timer 1 min up to 30 min per step
Polarization Index (PI), Dielectric Absorption ratio (DAR) and Dielectric Discharge (DD)
ratio measurements
PI = Rins (t2) / Rins (t1)
DAR = R1min / R15s
DD = Idis1min / C*U
Withstanding voltage (DC) up to 10 kV
Programmable ramp test voltage from 500 V up to 10 kV
High resolution ramp (approx. 25 V per step)
Programmable threshold current up to 5mA
Voltage and frequency measurement up to 600 V AC/DC
A dot matrix LCD offers easy-to-read results and all associated parameters. The operation
is straightforward and clear to enable the user to operate the instrument without the need
for special training (except reading and understanding this user manual)
Test results can be stored on the instrument. The new professional PC SW enables
straightforward transfer of test results and other parameters in both directions between the
test instrument and PC

HT7052
EN - 5
3 PREPARATION FOR USE
3.1 INITIAL INSPECTIONS
Before shipment, the instrument’s electronics and mechanics have been inspected. All
possible precautions have been taken in order for the instrument to be delivered without
damage
However, we recommend generally inspecting the instrument in order to detect any
damage suffered during transport. Should you detect any anomalies, immediately contact
the forwarding agent or the dealer
Moreover, we recommend checking that the package contains all parts listed in § 10.4.
Should you find any discrepancy, please contact the dealer. Should it become necessary
to return the instrument, please follow the instructions reported in § 11
3.2 INSTRUMENT POWER SUPPLY
The instrument is power-supplied through 6x1.2V IEC LR20 NiMH internal rechargeable
batteries which are recharged from the mains by means of a battery charger integrated in
the instrument itself. The symbol “ “ illuminated in the left bottom part indicates that
the batteries are flat and must be recharged. To recharge or replace the batteries, follow
the instructions given in § 10.2
CAUTION
Use only NiMh rechargeable batteries (IEC LR20)
Connect the instrument to the mains power supply for 20 hours to fully
charge batteries (typical charging current is 600mA). When you charge the
batteries for the first time, it normally takes about 3 charge and discharge
cycles for the batteries to regain full capacity
3.3 CALIBRATION
The instrument complies with the technical specifications reported in this manual. Its
correct operation is guaranteed for one year from the date of purchase
3.4 STORAGE
In order to guarantee accurate measurements and protect the instrument from possible
failures, after a long storage period under extreme environmental conditions, wait for the
instrument to return to a normal condition (see the environmental specifications listed in §
0)

HT7052
EN - 6
4 DESCRIPTION OF PARTS
4.1 INSTRUMENT DESCRIPTION
Fig. 1: Instrument description
LEGEND:
1 ON/OFF key to switch the instrument ON or OFF
2 START/STOP key to start or stop any measurement
3-4-5-6 , , ,arrow keys to select parameters and set values
7 SELECT key to enter set-up mode parameters
8 ESC key to exit the selected mode
9 MEM key to store, recall and erase results
10 Light key to turn the display backlight ON or OFF
11 Positive insulation resistance test terminal +OUTPUT
12 -13 GUARD test terminals intended to lead away potential leakage current
14 Negative insulation resistance test terminal –OUTPUT
15 Screw to fixing battery cover
16 Battery cover
17 USB galvanic port for connection to PC
18 RS-232 galvanic port for connection to PC
19 Mains connector to connect the instrument to the mains supply
20 LCD display
21 Label with serial number of the instrument

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EN - 7
4.2 DESCRIPTION OF TEST LEADS
Test lead 1
This test lead is designed for hand held testing of
insulation resistance
Features
Shielded cable in order to increase the immunity to
external disturb and improve the accuracy of
measurements
Insulation of yellow shielded cable: 12kVDC
Length cable = 2m
Test lead with double insulation and protection
10kVDC
Red banana connector with basic protection 10kVDC
and double protection 5kVDC
Green guard banana connector: CAT IV 600V
Test leads 2
These test leads is designed for diagnostic testing of
insulation
Features
Shielded cables in order to increase the immunity to
external disturb and improve the accuracy of
measurements
Insulation of yellow shielded cables: 12kVDC
Length cables = 2m
Red/black banana connectors with basic protection
10kVDC and double protection 5kVDC
Green guard banana connectors: CAT IV 600V
Red/Black alligator clips with basic protection
10kVDC and double protection 5kVDC
Guard test lead
This test lead is used in connection with the object on
test in order to reduce or cancel the surface leakage
current (see § 6.2)
Features
Cable banana-banana with protection CAT IV 600V
Alligator clip CAT IV 600V

HT7052
EN - 8
5 INITIAL OPERATIONS
5.1 SWITCHING ON THE INSTRUMENT
5.1.1 Mains powered instrument operation
CAUTION
If you connect instrument to the mains supply when instrument is turned
OFF, internal charger will begin to charge the batteries but instrument will
remain turned OFF. In button left angle of LCD, flashing battery indicator
will appear to indicate that the batteries are charging
If batteries are defective or missing and the instrument is connected
to the mains, the instrument do not switch on
If batteries are defective or missing, the charger will not work. In
button left corner of LCD screen only plug character will be appeared
If the instrument is connected to the mains supply when the instrument is
turn ON, the instrument will automatically switch from the battery supply to
the main supply. In button left corner of the LCD screen, the plug character
will appear
If instrument is not in measuring mode*, the internal charger will begin to
charge the batteries. In button left corner of LCD screen battery indicator
will start to flash, indicating that the batteries are charging
It is recommended to DO NOT connect or disconnect the instrument to
mains supply while the instrument is in measuring mode
5.1.2 Backlight operation
Instrument supplied by the batteries
After turning the instrument ON the LCD backlight is automatically turned ON. It can be
turned OFF and ON by simply clicking the LIGHT key
Instrument supplied by the mains
After turning the instrument ON the LCD backlight is automatically turned OFF. It can be
turned OFF and ON by simply clicking the LIGHT key
Auto power OFF
The instrument can be switched OFF only by pressing the ON/OFF key. The auto-off
function is not available to allow long-term measurements to be performed
5.1.3 Autocalibration
The instrument is switched ON by pressing the ON/OFF key. After turning on, the
instrument will perform the autocalibration (see Fig. 3). Measuring test leads should be
disconnected during autocalibration. If not, the autocalibration procedure could be false
and instrument will require disconnection of the test leads and repeat switching OFF and
ON
Fig. 2: Spash screen Fig. 3: Autocalibration Fig. 4: Main menu
After finishing the autocalibration, the main menu (see Fig. 4) will appear and instrument
is ready for normal operation

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EN - 9
Auto-calibration prevents the reduction in accuracy when measuring very low currents. It
compensates the effects caused by ageing, temperature and humidity changes etc. A new
auto-calibration is recommended when the temperature changes by more than 5C. If the
instrument detects an incorrect state during the autocalibration, the following warning
message will be displayed:
CAUTION
TEST LEADS CONNECTED: DISCONNECT AND SWITCH ON THE
INSTRUMENT AGAIN
CONDITIONS OUT OF RANGE: PRESS START TO CONTINUE
Possible reasons for out of range conditions are excessive humidity, excessively high
temperature, etc. In this case it is possible to perform measurements by pressing the
START/STOP button again but results could be out of technical specification
5.2 CONFIGURATION AND SETUP OF SYSTEMS PARAMETERS
The configuration and setup function enables the selection and adjustment of the
parameters (see Table 1) that are not directly involved in the measurement procedure (see
Fig. 5 and Fig. 6). In the lower section of the display the power supply status is shown
Fig. 5: Configuration menu Fig. 6: Setup menu
PARAMETERS VALUE DESCRIPTION
Memory clear Clear all memory locations
Filter Fil1, Fil2, Fil3, Fil0 Selection of noise rejecting filter (see § 6.3)
DIAG. Starting
time 0%…90%
Adjustment of start of the timer in the
DIAGNOSTIC TEST functions, according to the
nominal voltage Unominal. See additional
explanation in § 6.1)
Contrast 0%…100% Adjustment of the LCD contrast
Time Set real time (hour: minute)
Date Set current date (day-month-year)
COM port RS232 2400, RS232 4800,
RS232 9600,RS232 19200,
USB 115000 Set communication mode and rate
Language Ita, Eng, Esp, Deu Set system language
Initialization For internal factory and service maintenance
only
Table 1: Configuration of system parameters
1. Use and arrows to select parameter (line) to be adjusted
2. Use or arrows to change the value of the selected parameter. If there are two or
more sub-parameters in one line (e.g. date and time) then use the SELECT key to skip
to the next sub-parameters and back
3. Press the ESC key to exit from configuration and back to the main menu

HT7052
EN - 10
6 HOW TO PERFORM THE MEASUREMENTS
6.1 THEORY OF INSULATION RESISTANCE MEASUREMENT
The purpose of insulation tests
Insulating materials are important parts of almost every electrical product. The material’s
properties depend not only on its compound characteristics but also on temperature,
pollution, moisture, ageing, electrical and mechanical stress, etc. Safety and operational
reliability require the regular maintenance and testing of the insulation material to ensure it
is kept in good operational condition. High voltage tests are used to test insulating
materials
DC vs. AC testing voltage
Testing with a DC voltage is widely accepted as being useful as testing with AC and / or
pulsed voltages. DC voltages can be used for breakdown tests especially where high
capacitive leakage currents interfere with measurements using AC or pulsed voltages. DC
is mostly used for insulation resistance measurement tests. In this type of test, the voltage
is defined by the appropriate product application group. This voltage is lower than the
voltage used in the withstanding voltage test so the tests can be applied more frequently
without stressing the test material
Typical insulation tests
In general, insulation resistance tests consist of the following possible procedures:
Simple insulation resistance measurement also called a spot test
Measurement of the relationship between voltage and insulation resistance
Measurement of the relationship between time and insulation resistance
Test of residual charge after the dielectric discharge
The results of this test can indicate whether the replacement of the insulation system is
required. Typical examples of where testing insulation resistance and its diagnosis are
recommended are transformer and motor insulation systems, cables and other electrical
equipment
Electrical representation of insulating material
The represents the equivalent electrical circuit of an insulating material
Riso Cpi
Rpi
Ciso
Riss1
Riss2
material
surface Itest
+
-
Guard
IPI
ICiso IRiso IRiss
Itest
Fig. 7: Equivalent electrical circuit Fig. 8: Current graphs

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EN - 11
Riss1, Riss2 = surface resistivity (position of optional guard connection)
Riso = the actual insulation resistance of material
Ciso = capacitance of material
Cpi, Rpi = represents polarization effects
The Fig. 8 shows typical currents for that circuit, where:
Itest = overall test current (Itest= IPI+ IRISO+ IRISS)
IPI = polarization absorption current
IRISO = actual insulation current
IRISS = surface leakage current
Basic Insulation resistance test
Virtually every standard concerning the safety of electrical equipment and installations
requires the performance of a basic insulation testing. When testing lower values (in the
range of M), the basic insulation resistance (Riso) usually dominates. The results are
adequate and stabilize quickly
It is important to remember the following:
The voltage, time and limit are usually given in the appropriate standard or regulation
Measuring time should be set to 60 s or the minimum time required for the Insulation
capacitance Ciso to be charged up
Sometimes it is required to take ambient temperature into account and adjust the result
for a standard temperature of 40C
If surface leakage currents interfere with the measurements (see Riss above) use the
guard connection (see § 5.2.). This becomes critical when measured values are in the G
range
Voltage dependence test – Step voltage test
This test shows if the insulation under test has been electrically or mechanically stressed.
In this instance the quantity and size of insulation anomalies (e.g. cracks, local
breakdowns, conductive parts, etc). is increased and the overall breakdown voltage is
reduced. Excessive humidity and pollution have an important role especially in the case of
mechanical stress. If the results of successive tests show a reduction in the tested
insulation resistance the insulation should be replaced
In this function the instrument measure the insulation resistance by considering 5 equal
time intervals with the test voltage divided from 1/5 of nominal value to the set nominal
value (see Fig. 9)
Fig. 9: Insulation measurement with step voltage test

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EN - 12
6.1.1 Time dependence test – Diagnostic test
Diagnostic test is a long duration test for evaluating the quality of the insulation material
under test. The results of this test enable the decision to be made on the preventive
replacement of the insulation material
DIELECTRIC ABSORPTION RATIO (DAR)
DAR is ratio of Insulation Resistance values measured after 15s and after 1 minute. The
DC test voltage is present during the whole period of the test (also an Insulation
Resistance measurement is continually running). At the end, the DAR ratio is displayed:



s
DAR
R
R
iso
iso 15
min1

Some applicable values:
DAR value Tested material status
< 1.25 Not acceptable
< 1.6 Considered as good insulation
> 1.6 Excellent
When determining Riso (15s) pay attention to the capacitance of the test object. It has to
be charged-up in the first time section (15s). Approximate maximum capacitance using:




V
s
FU
t
C103
max
.


where:
t = period of first time unit (e.g. 15s)
U = test voltage.
To avoid this problem, increase the DIAG. Starting time parameter in CONFIGURATION
menu, because start of timer in the DIAGNOSTIC TEST functions depends on the test
voltage. The timer begins to run when test voltage reaches the threshold voltage, which is
product of the DIAG. Starting time and nominal test voltage (Unominal)
Using filters (fil1, fil2, fil3) in the DAR function is not recommended!
Analysing the change in the measured insulation resistance over time and calculating the
DAR and PI are very useful maintenance tests of an insulating material

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EN - 13
POLARIZATION INDEX (PI)
PI is the ratio of Insulation Resistance values measured after 1 minute and after 10
minutes. The DC test voltage is present during the whole period of the measurement (an
Insulation Resistance measurement is also running). On completion of the test the PI ratio
is displayed:



min1
min10
R
R
iso
iso
PI 
General applicable values:
PI value Tested material status
1 to 1.5 Not acceptable (older types)
2 to 4 (typically 3) Considered as good insulation (older types)
>4(very high insulation resistance) Modern type of (good) insulation systems
When determining Riso (1min) pay close attention to the capacitance of the object under
test. It has to be charged-up in the first time section (1 min). Approximate maximum
capacitance using:




V
s
FU
t
C103
max
.


where:
t = period of first time unit (e.g. 1min)
U = test voltage
To avoid this problem, increase the DIAG. Starting time parameter in CONFIGURATION
menu, because start of timer in the DIAGNOSTIC TEST functions depends on the test
voltage. The timer begins to run when test voltage reaches the threshold voltage, which is
product of the DIAG. Starting time and nominal test voltage (Unominal)

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EN - 14
DIELECTRIC DISCHARGE RATIO (DD)
An additional effect of polarization is the recovered charge (from Cpi) after the regular
discharging of a completed test. This can also be a supplementary measurement for
evaluation of the quality of insulating material. This effect is generally found in insulating
systems with large capacitance Ciso. The polarisation effect (described in “Polarisation
Index”) causes a capacitance to form (Cpi). Ideally this charge would dissipate
immediately a voltage was removed from the material. In practice, this is not the case
DD is the diagnostic insulation test carried out after the completion of the Insulation
Resistance measurement. Typically the insulation material is left connected to the test
voltage for 10 30 min and then discharged before the DD test is carried out. After 1
minute a discharge current is measured to detect the charge re-absorption of the insulation
material. A high re-absorption current indicates contaminated insulation (mainly based on
moisture:


 
FCVU mAIdis
DD .
min1

where:
Idis 1min = discharging current measured 1 min after regular discharge
U= test voltage
C= capacitance of test object
General applicable values:
DD Value Tested material status
> 4 Bad
2 - 4 Critical
< 2 Good

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EN - 15
6.1.2 Withstanding voltage test
Some standards allow the use of a DC voltage as an alternative to AC withstanding
voltage testing. For this purpose the test voltage has to be present across the insulation
under test for a specific time. The insulation material only passes if there is no breakdown
or flash over. Standards recommend that the test starts with a low voltage and reaches the
final test voltage with a slope that keeps the charging current under the limit of the current
threshold. The test duration normally takes 1 min
The instruments offers Withstanding Voltage test of insulation material. It covers two types
of tests:
Breakdown voltage testing of high voltage device, e.g. transient suppressors and
DC withstanding voltage test for insulation coordination purposes
Both functions require breakdown current detection. The test voltage increases step by
step from the Start up to the Stop value over a predefined time and it is kept at the Stop
value for a predefined test time (see Fig. 10 – left part) or it happens the breakdown on
device under test (see Fig. 10 – right part)
Fig. 10: Withstanding test without breakdown (left) and with breakdown (right)
Ut = test voltage
t = time
Ustart = starting voltage
Ustep = voltage step approx. 25 V (fixed value - not modify)
Ustop = end test voltage
Tstep = test voltage duration per step
Tend = constant test voltage duration after reaching End value
Ub = breakdown voltage
Humidity and insulation resistance measurements
When testing outside the reference ambient conditions, the quality of the insulation
resistance measurements can be affected by humidity. Humidity adds leakage paths onto
the surface of the complete measuring system, (i.e. the insulator under test, the test leads,
the measuring instrument etc). The influence of humidity reduces accuracy especially
when testing very high resistances (e.g. T). The worst conditions arise in environments
containing high condensation, which can also reduce safety. In the case of high humidity, it
is recommended to ventilate the test areas before and during the measurements. In the
case of condensed humidity the measuring system must dry and it can take several hours
or even few days to recover

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EN - 16
6.2 GUARD TERMINAL
The purpose of the GUARD terminal is to lead away potential leakage currents (e.g.
surface currents), which are not a result of the measured insulation material itself but are a
result of the surface contamination and moisture. This current interferes with the
measurement i.e. the Insulation Resistance result is influenced by this current. The
GUARD terminal is internally connected to the same potential as the negative test terminal
(black one). The GUARDs test clip should be connected to the test object so as to collect
most of the unwanted leakage current (see Fig. 11)
Fig. 11: Principle scheme relative to the Guard terminal
where:
Ut.....................Test voltage
IL......................Leakage current (resulted by surface dirt and moisture)
IM......................Material current (resulted by material conditions)
IA......................Test current
Result without GUARD terminal: RINS = Ut / IA= Ut / (IM+ IL) Incorrect result
Result using GUARD terminal: RINS = Ut / IA = Ut / IMcorrect result
The GUARD terminal it is internal connected at the same negative test lead (black). The
alligator clip should be connected to the object on test in way to detect the most possible
leakege current (see Fig. 12)
Fig. 12: Connection of the Guard terminal to the object on test
CAUTION
It is recommended to use the GUARD connection when high insulation
resistance (> 10G) should be measured
The guard terminal is protected by an internal impedance 400k
The instrument has two guard terminals to allow easy connection of
shielded measuring leads

HT7052
EN - 17
6.3 USE OF INTERNAL FILTERS
Filters are built in to reduce the influence of noise on measurement results. This option
enables more stable results especially when dealing with high Insulation Resistances
(Insulation Resistance, Diagnostic Test, Step Voltage). In these functions, the status of the
filter option is shown in the top right corner of the LCD screen. The below table contains a
definition of the individual filter options
Filter options Description
Fil0 Low pass filter with cut off frequency of 0.5 Hz in signal line
Fil1
A
dditional low pass filter with cut off frequency of 0.05 Hz in
the signal line
Fil2 Fil1 with increased integrating time (4 s)
Fil3 Fil2 with additional cyclic averaging of 5 results
Table 2: Filter options
6.3.1 The purpose of filtering
The internal filters smooth the measured currents by means of averaging and bandwidth
reduction. There are various sources of disturbance:
AC currents at the mains frequency and its harmonics, switching transients etc, cause
the results to become unstable. These currents are mostly cross talk through insulation
capacitances close to live systems
Other currents induced or coupled in the electromagnetic environment of the insulation
under test
Ripple current from internal high voltage regulator,
Charging effects of high capacitive loads and / or long cables.
Voltage changes are relatively narrow on high resistance insulation, so the most important
point is to filter the measured current
CAUTION

A
ny of the selected filter options increases the settling time with Fil1 to 60
s, Fil2 to 70 s, and Fil3 to 120s
It is necessary to pay close attention to the selection of time intervals when
using the filters
The recommended minimum measuring times when using filters are the
settling times of the selected filter option
Example:
A noise current of 1mA/50Hz adds approximately 15% distribution to the measured result
when measuring 1G.
By selecting FIL1 option the distribution will reduce to less than 2 %
In general using FIL2 and FIL3 will further improve the noise reduction

HT7052
EN - 18
6.4 VOLTAGE MEASUREMENT
CAUTION
Maximum input for DC or AC voltage is 600V. Do not attempt to take any
voltage measurement that exceeds the limits. Exceeding the limits could
cause electrical shock and damage the instrument
1. Switch on the instrument by pressing the ON/OFF key
2. Select with arrow keys or the item “VOLTAGE” on main menu and confirm with
SELECT key. The screen of Fig. 13 is shown by the meter
Fig. 13: Initial screen of voltage measure Fig. 14: Screen of measured value
3. Connect the red part of the Test lead 1 or Test leads 2 (see § 4.2) to the +OUTPUT
input and the black part of the Test leads 2 (see § 4.2) to the –OUTPUT input
4. Connect the tip of Test lead 1 or Test leads 2 (positive) and the black cable of Test
leads 2 (negative) to the object on test respect the polarities for DC voltage
measurement (see Fig. 15)
Fig. 15: Connection of meter for voltage measurement
5. Press START/STOP key to activate the measurement in continuous mode
6. Press again the START/STOP to stop the measurement. The result of test is shown at
display (see Fig. 14)
7. For saving the result see § 7