Megger MFT1741 User manual

MFT1741 and MFT1845
Multifunction Testers
MFT Addendum
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User Guide Addendum - MFT1741-MFT1845 www.megger.com 2
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Contents
EN - Addendum to Section 7.0 4
CN - 对第 7.0 节的增补 9
DE - Nachtrag zu Abschnitt 7.0 14
EL - Προσάρτημα στην Ενότητα 7.0 19
ES - Apéndice para la sección 7.0 24
FR - Addendum à la section 7.0 29
IT - Appendice alla Sezione 7.0 34
NL - Addendum bij paragraaf 7.0 39
PL - Uzupełnienie do rozdziału 7.0 44
SK - Dodatok k časti 7.0 49
SV - Tillägg till avsnitt 7.0 54
ZH - 第 7.0 章的增補 59

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Addendum to Section 7.0
Supplementary information for the MFT1741 and
MFT1845 User Guide
Applies to: Loop Impedance Tests (MFT1741 and MFT1845
only).
New feature: Con󰘰dence Meter (Patent Applied For) for non-trip
(3Lo) loop impedance tests.
Display information:
Con󰄈dence Meter Function (Patent Applied For)
Variable test results in a Loop Impedance test are usually
a result of electrical noise on the circuit during the test. The
Con󰘰dence Meter analyses this electrical noise and, if necessary,
automatically extends the duration of the test to arrive at an
accurate 󰘰gure (as per the instruments stated accuracy).
The analogue arc is used to indicate the degree of con󰘰dence in
the accuracy of a measurement.
Figure 1. Instrument Display
Con󰘰dence
meter
3Lo (3 wire
non-trip)
Mode indicator
Noise detected
Standard non-trip loop
impedance mode test
indicator
Non-trip loop impedance test
mode for circuits with Type B
RCD
Test “in progress”
warning
Units of
measurement

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During a test the analogue arc will reduce as the degree of
con󰘰dence in the measurement increases. As the in󰘱uence of
electrical noise on the measurement is removed the analogue
arc reduces down to one element. At this point the test stops and
a 󰘰nal result is shown.
The arc may 󰘱uctuate during a test and the shown digital value
will change as the Con󰘰dence Meter analyses the electrical noise
and corrects the value.
3Lo Loop Impedance Measurement
Note: Test leads should not be disconnected during a test, as the
sudden interruption of the test current could be detected by an
RCD as a leakage fault and cause a trip. If this is considered to
be potentially inconvenient or hazardous, change 3Lo from AC/A
to Bmode. This will reduce the risk of the RCD tripping.
Important: It is impossible to guarantee that an RCD will not
trip as the RCD may be out of speci󰘰cation, subject to additional
external in󰘱uences, incorrectly connected or faulty. In this
instance alternative methods to test the circuit characteristics are
recommended, for example, the R2 method.
1. Select L-PE.
2. Connect the Live, Neural and Earth test leads of the
MFT to a live circuit. The display will show the standard
warning screen.
Figure 2. Analogue Arc
Initial valueStart Analysing noise Finished

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The display will show , which indicates the suitability
for use on circuits protected by a Type AC or a Type A RCD, or
RCBO.
If the RCD on the circuit is a Type B, press and hold until
the display shows (Type B RCD).
Note: If unsure of the RCD type use Type B setting.
3. Press TEST. The display will show the start of a Loop
Impedance con󰘰dence test, followed by an initial value of
loop impedance:
Figure 3.
3Lo Connection Options
Figure 4. Live Circuit
Warning Screen
L
N
E
MCB RCD
g
I
CAT IV
300V
12-15V
1.2A
RCD
g
L
N
E
MCB
I
CAT IV
300V
12-15V
1.2A
> then >
Figure 5. Loop Impedance Test Start Screen

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Note: The test is not 󰘰nished until the analogue arc reduces to
one element, or the TEST button is pressed again.
4. If no noise is detected the analogue arc will reduce to a
single element and the display will show a completed test
result. The 󰘰nal value may vary slightly if very small levels
of noise were detected.
5. If electrical noise is detected, the instrument analyses
it continuously and the analogue arc will reduce as the
electrical noise is 󰘰ltered from the measurement. Even
if there is a lot of electrical noise, the con󰘰dence of the
measurement will improve with time and the analogue arc
will reduce, so that a 󰘰nal stable value will show at the
end.
(electrical noise symbol) will also show to indicate the
presence on electrical noise on the circuit.
If the electrical noise in the circuit varies the analogue arc may
󰘱uctuate until the test has completed and the analogue arc shows
a single element.
Figure 6. Final Result
Figure 7. Analogue Arc Fluctuation
Start Small noise
Momentarily
higher noise Complete

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Note: The maximum measurement time is three minutes. If
after three minutes there is still more than one element in the
analogue arc, the test will stop. More than one element shows
that the instrument has not achieved its desired con󰘰dence level
(electrical noise is high). The test is still valid, but with reduced
accuracy.
6. Press TEST at any time to stop the test. A digital test
result will show and the size of the analogue arc shows
the degree of con󰘰dence in the test result (smaller the
analogue arc = more con󰘰dence).

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对第 7.0 节的增补
MFT1741 和 MFT1845《用户指南》的补充资料
适用于：回路阻抗测试（仅限 MFT1741 和 MFT1845）。
新功能：准确性评估计（已申请专利），用于不跳闸的 (3Lo) 回路
阻抗测试。
显示信息:
准确性评估计功能（已申请专利）
回路阻抗测试中出现的测试结果波动现象通常是由于测试期间电路
中的干扰引起的。准确性评估计会分析此干扰，并在必要时自动延
长测试的持续时间，以获得一个精确的数值（按照仪器所声明的精
确度）。
图 1. 仪器显示
准确性评
估计
3Lo（3 线不
跳闸）模式指
示器
检测到干扰
标准的不跳闸回路阻抗
模式的测试指示器
不跳闸的回路阻抗测试模式，
适用于使用 B 型 RCD 的电路
测试“正在进行”
警告
测量单位
CN

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准确性评估计采用了模拟表头来指示测量精确度的可信度。
在测试期间，模拟表头会随着测量中可信度的增加而缩小。当干
扰对测量的影响被去除时，模拟表头会缩小为一个刻度。此时测
试停止，并显示最终结果。
此模拟表头在测试期间可能会波动，所示的数字值会随着准确性
评估计对干扰的分析以及对该值的修正而变化。
3Lo 回路阻抗测量
备注: 测试引线在测试过程中不得断开，因为测试电流的突然中断
会被 RCD 视作发生了漏电故障并引起跳闸。如果认为这种情况会
带来潜在不便或危险，请将 3Lo 从 AC/A 切换到 B 模式。这样将
会减少 RCD 跳闸的风险。
重要事项: 由于其他外部影响因素、错误接线或故障的原因，导致
RCD 可能会检测到超出额定值的信号，因此无法保证 RCD 不会
跳闸。在这种情况下，建议采用备选方法来测试电路的特性，例
如 R2 方法。
1. 选择 L-PE。
2. 将 MFT 的火线、零线和接地测试引线连接到一个带电电
路。显示屏将显示标准的警告界面。
图 2. 模拟表头
初始值开始 干扰分析中 结束