MULTI MEASURING INSTRUMENTS MET-1 Instruction Manual

Thank you very much for selecting our clamp earth tester.
This model is complex instrument and employs a very reliable
mechanical/electronic design. Before you use your new
instrument, read this instruction manual completely and
familiarize yourself thoroughly with all functions. With proper
use and care, your tester will give you years of satisfactory
service.

Multi Measuring Instruments Co., Ltd.

Akihabara murai-Bldg. 7F,
1-26 Kanda Sakuma-cho,
Chiyoda-ku, Tokyo, 101-0025 Japan
Tel: [phone]
Fax: [phone]

Clamp Earth Tester

MET-1

Instruction Manual

CONTENTS

1. General………………………………………………………………………….....1

2. Safety summary………………………………………………………………... 2-3

3. Measuring principle of clamp earth tester………………………………………4-5

4. Specification……………………………………………………………………..6-7

5. Panel description…………………………………………………….…………..8-9

6. Preparation before use…………………………………………………………...10
6-1. Battery charging……………………………………………………………..10
6-2. Rechargeable battery……………………………………………………….10

Precaution on charging battery…………………………………………….....10-11

7. Operation…………………………………………………………………………12
7-1. AC current measurements………………………………………………….12

7-2. Earth resistance measurements………………………………………..13-14

7-3. Measurement by TERMINALS Out mode...........................……………….15

8. Measuring example……………………………………………………………....16

8-1. Electric installation…………………………………………………..........16-17

8-2. Earth resistance measurements for the outdoor appliance………………..18
8-3. Earth resistance measurements for multiple earth system………………...18
8-4. Earth resistance measurements for the earthing electrode………………..19
8-5. Earth resistance measurements for telecommunication system………….20
8-6. Measurements for the earting connection of the outlet…………………….20

8-7. Measurement for the active line........................................................................21

8-8. Measurement where L & C are low..................................................................21

9. Maintenance……………………………………………………………………...22

10. Warranty………………………………………………………………………….22

1. General

The periodic measurement of earth electrode resistance is indispensable to
ensure the safety for electrical installation.

The ordinary earth electrode test method requires the use of auxiliary test spikes
or rods for the measurements.

New clamp earth tester provides simple and quick measurements for earth
electrode resistance without lazy spiking work. The new spike-less method is
the loop measurements by the operation of two clamps (CTs).

One CT injects a superimposing voltage into the circuit and the other CT
measures the injected current of the loop circuit. In our clamp earth tester, the
auto sweep signal (4kHz to 400kHz, 160mV p-p) is used and injected into the
loop circuit. When the resonance phenomenon is caused at the certain
frequency by the inductance and capacitance in the circuit, the current flow
becomes maximum. The injected current into the circuit is proportional to the
loop resistance. And this current is measured by CT and converted to the earth
resistance value.

Please refer to “chapter 3. Measuring principle of clamp earth tester” about
details.

Before you use MET-2, read this instruction manual completely and understand
yourself thoroughly with all functions.

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WARNING

●The instrument is designed to measure for the low voltage circuit. Do not
make measurements of power lines carrying more than AC 500V.

●POSSIBLE ELECTRICAL SHOCK. Do not make measurements if the
case or CT is damaged.

●POSSIBLE ELECTRICAL SHOCK or FIRE HAZARD. Do not expose this
instrument to rain or moisture. Do not operate the tester in the presence of
flammable gasses or fumes.

●Never fail to keep the maximum tolerable input. Make measurements
within the rated current.

●Never make measurements with the case opened.

●Never operate this instrument if it becomes wet, damp or has any liquid

condensation build-up on any part of the instrument.

●Never make measurements for un-insulated conductors or bus bars.

2. Safety summary

This instrument has been manufactured and tested in accordance with safety
regulations IEC 61010-1/EN 61010-1 and IEC 61010-2-032/EN 61010-2-032.
If used for its intended purpose, safety of the user and of the instrument is
assured. The device may only be operated by properly trained personnel who
are capable of recognizing the dangers associated with the measurement of
electrical current and voltage.

Read the operating instructions completely and carefully before using the
instrument, and follow all instructions included therein.

Meaning of symbols on the instrument:

Warning concerning a source of danger
(Refer to the manual before use.)

The instrument is protected by double or reinforced insulation

- 2 -

- 3 -

CAUTION

●Do not use or storage the instrument under the direct sunshine, high
humidity and temperature, as it may cause the insulation defect of the
instrument.

●Do not use the instrument nearby the appliance or machine which generate
the strong magnetic field, as it may cause the measuring error of instrument.

●Do not apply the mechanical vibration or shock to the instrument.

●Before operating this instrument, familiarize yourself with all instructions

outlined in this manual.

●Always check to make sure that the function switch is set to the proper
position.

●When making measurements, use CAUTION as dangerous voltages may
be present in normally safe areas.

●To avoid electrical shock, use CAUTION when working above 60V DC or
25V AC rms. Such voltages pose a shock hazard.

●Do not apply the voltage more than AC 10V to the input and output
terminals.

●Do not pull the CT cable, as it may cause damages.

●Do not disassemble the instrument.

●If excessive current is applied to the CT, the instrument will be heated and

damaged. Use the CT within the rated current.

●The rechargeable batteries are used in the instrument. Do not mix with
normal batteries, as it is very dangerous.

●The power supply voltage of battery charger is AC 200～240V. Do not
apply higher voltage to the charger, as it may cause the damage to the
instrument and or the electrical accident.

●The charging batteries lose some of their capacity when repeatedly
charged/discharged. The actual decrease of capacity versus number of
charging cycles depend on battery type.

3. Measuring principle of clamp earth tester

Block diagram

- 4 -

Equivalent circuit

The block diagram and equivalent circuit show the measuring principle of
CLAMP EARTH TESTER.

When the auto sweep signal (4kHz to 200kHz, 160mV p-p) is injected into the
circuit, the resonance phenomenon is caused at the certain frequency by
inductance (L) and electrostatic capacity (C0) or DC resistance (r) and
electrostatic capacity (C1) in the circuit, and the current flow (i) is caused. When
the resonance phenomenon is caused, the current flow (i) become maximum.
The injected current (i) into the circuit is proportional to the earth resistance (RB)
and this current (i) is measured by the measuring CT and used for the
computation of the earth resistance value (RB) with other calculation factors.
The resonance phenomenon is caused almost at 4kHz to 200kHz frequency in
our field test.

Note: If the resonance phenomenon is not caused in the circuit, the current

flow (i2) is caused and the measured resistance value become RB + RD
+Zc. This resistance value will be higher than the actual value
abnormally, or over range indication “OVER” will be displayed.

- 5 -

4. Specification

Measuring function : Earth resistance, AC current (Load & leakage)
A/D conversion : Dual slope integration mode
Safety standard : IEC 61010-1,IEC61010-2-032

Installation CATⅡ600V or CATⅢ300V

Sampling : Approx. 2 times/second for AC current
Measuring time : Approx. 30 second for earth resistance

Display : LCD16 letters/characters x 2 line with contrast

adjuster
Over range indication : “OVER” on LCD
Low battery indication : “B” mark on LCD
Data hold indication : “DH” mark on LCD for AC current measurement
Detection method : Synchronous detection

Accuracy (23°C ± 5ºC, 80% RH or less) :

Earth resistance (Earth current: Less than 1A)

Range Resolution Accuracy
Less than 10Ω 0.1Ω ±0.5Ω
10 ~ 50Ω 0.1Ω ±2.0Ω
50 ~ 150Ω 0.1Ω ±5.0Ω
150 ~ 200Ω 0.1Ω ±20Ω

Note:

Accuracy is specified by standard resistance with following test configuration.

- 6 -

Induction CT

Measuring CT