Megger DET14C Manuale utente

DET14C and DET24C

Digital Earth Clamp-on Tester

USER GUIDE

GSAFETY WARNINGS

These safety warnings are provided to ensure the safety of personnel and proper operation of the instrument.

■Safety warnings and precautions must be read and understood before the instrument is used. They must be observed during use.

■Do not leave the instrument connected to the system under test when not in use.

■Do not touch circuit connections and exposed metalwork of the installation or equipment under test.

■Do not use the instrument or connect it to any external system if it shows any visible signs of damage, malfunction or if it has been stored in unfavourable

conditions.

■Always keep body parts behind the tactile barrier on the handles of the instrument.

■Always inspect the instrument prior to use. Replace any defective parts immediately or return the instrument to an authorised service centre for repair.

■Do not use the instrument or connect it to any external system if the casing is open or any parts of the case are missing.

■Do not use rechargeable batteries in this instrument.

■Always use caution when clamping the instrument around energised electrical conductors.

■Always use extreme caution when clamping around bare conductors: under fault conditions, high voltages and currents may be present and may pose a shock

hazard.

■The instrument is not suitable for measuring AC currents in multi-core cables or DC currents.

■The instrument should not be used if any part of it is damaged.

■This instrument is not intrinsically safe and must not be used in hazardous atmospheres.

■If this equipment is used in a manner not specified by the manufacturer, the protection provided by the equipment may be impaired.

■Use extreme caution when using the instrument in proximity to bare conductors. Avoid contact between the metal in the jaws and bare conductors. A short

circuit would create an arc-flash explosion hazard

NOTE:

THE INSTRUMENT MUST ONLY BE USED BY SUITABLY TRAINED AND COMPETENT PERSONS.

Users of this equipment and/or their employers are reminded that National Health and Safety Legislation requires them to carry out valid risk assessments of all

electrical work so as to identify potential sources of electrical danger and risk of electrical injury such as inadvertent short circuits.

The safety warnings provided in this document are indicative of safe practice and shall not be considered exhaustive. Additionally, they are not intended to replace

local safety procedures where the instrument is being used.

CONTENTS

GSAFETY WARNINGS..................................................................... 2

CONTENTS....................................................................................... 3

GENERAL DESCRIPTION ................................................................ 4

APPLICATION................................................................................... 6

MODES OF OPERATION................................................................. 8

GENERAL OPERATION.................................................................... 9

GENERAL SPECIFICATIONS ......................................................... 12

MEASUREMENT SPECIFICATIONS............................................... 14

ORDERING INFORMATION AND ACCESSORIES........................ 15

PREVENTATIVE INSTRUMENT MAINTENANCE.......................... 15

REPAIR AND WARRANTY .............................................................. 17

Symbols used on the instrument

GCaution: refer to accompanying notes.

tEquipment protected throughout by Double

Insulation.

cEquipment complies with current EU directives.

N13117

Equipment complies with current “C tick”

requirements.

Do not dispose of in the normal waste stream.

Equipment can be clamped around and removed

from hazardous live conductors [IEC 61010-2-032

Type A clamp].

Equipment not suitable for use where the

magnetic field exceeds this limit.

CAT IV 600 V

Overvoltage category IV (equipment installed at or

near the origin of the electrical supply to a

building.)

600 V refers to the rms phase-to-earth voltage that

this instrument can withstand to the overvoltage

category IV rating.

GENERAL DESCRIPTION

The DET14C and DET24C represent a new generation of

earth/ground clamp-on resistance testers. These instruments

induce a test current into earth systems and measure ground

resistance in multi ground installations without needing to

disconnect the ground. They offer market leading access,

advanced features, simple operation and CAT IV 600 V safety

protection.

Designed with flat core ends, they prevent dirt build up,

ensuring measurement integrity and improved reliability over

products with interlocking teeth. Other enhancements over

current generation products include improved accuracy and up

to 300% increase in battery life. In electrically noisy

environments the built-in filter function offers increased noise

immunity.

DET14C and DET24C also offer a true RMS AC current

measurement facility up to 35 Amps. The instrument’s ability to

measure current flowing in an earth cable is a useful safety

feature, especially if the earth cable has to be disconnected. A

high current flow to earth could draw an arc on disconnection

with potentially severe consequences.

The elliptical shaped head design offers improved access to

cables and earth straps in constrained spaces (locations). The

clamp head accommodates up to 39 mm diameter cable and

50 mm earth tapes making them suitable for use in power

stations, sub-stations, towers and many more facilities. Operation

in dark and restricted areas is facilitated by a display with

backlight and an audible tone associated with the hold key. (The

special jaw opening mechanism ensures proper jaw closure yet

minimises the force required to open them).

The DET14C offers storage of results for later on-screen recall

and the DET24C supports a download of results via IrDA-to-USB

link into PowerDB and Power DB Lite, Megger’s Acceptance &

Maintenance Test Data Management software. Stored data is

indexed using a sequential serial number together with a time

and date stamp for each record.

FEATURES AND BENEFITS

■39 x 55 mm elliptical head

■Auto-current measurement safety feature

■Memory to record and view results

■Automatic self calibration

■Auto ranging

■High and low alarms

■Real time clock for date and time stamping of results

DET24C ADDITIONAL FEATURES

■IrDA USB interface to PC

■Advanced memory functionality with download

■Megger PowerDB/PowerDB LiteTM compatible

Figure 1: DET14C / DET24C Instrument Front View

Figure 2: DET14C / DET24C Instrument Rear View

1. Clamp jaws

2. Tactile barrier

3. Rotary switch

4. HOLD button

5. LCD display

6. Keypad

7. Tactile barrier

8. Lever

9. Battery cover/label

Figure 3: DET14C / DET24C Instrument Bottom

View

1. Wrist strap loop

2. IrDA window

Figure 4: DET14C / DET24C Instrument Display

View

Save Tick = set

Open Cross = not set

Delete Warning refer to user guide

IrDA download Signal noise detected

Alarm Less than

Filter More than

Battery

Hold

Date formats

Hours, minutes, seconds

Clamp open

APPLICATION

The DET14C / DET24C digital earth clamp meters are particularly

suitable for measuring earth resistance in various installations

such as buildings, pylons and RF transmitter sites without system

disconnection. In addition, they can be used for the inspection

and verification of lightning protection systems and virtually any

installation where a current loop can be generated.

Principle of Operation

A defined test voltage is injected into the system under test using

a voltage transducer coil to induce a current, I, to flow which can

be measured by the current sensing coil. The resistance follows

from Ohm’s law, R = V/I.

The system shown in Figure 5 can be simplified to the resistance

of the electrode under test, Rg and the resistance of the other

electrodes in parallel, i.e. R1 || R2 || R3… || Rn. Therefore, the

current induced by the test voltage is I=V/[Rg+(R1 || R2 ||

R3… || Rn)]. It follows that as the resistance of the other

electrodes in parallel approaches zero, then the resistance

measured, approaches the value of the electrode under test.

Figure 5: Example earthing system suitable for

clamp meter

MODES OF OPERATION

The DET14C / DET24C can operate in one of three main modes,

selected using the rotary switch:

OFF – Turn instrument off

Ω- Resistance measurement

A - Current measurement

Fn - Setup and configuration

When in a measurement mode, there are other functions which

are selected using the buttons:

HOLD – Hold the displayed measurement value.

– Enable / disable display backlight.

- Enable / disable buzzer function.

- Save displayed result to memory.

When in the setup and configuration mode (Fn), some buttons

have different functions:

- Increment value.

- Decrement value.

- Advance to next field.

OK – Accept value.

Figure 6: Main mode selection using the rotary

switch

Figure 7: Other functions using buttons

GENERAL OPERATION

Powering on the Instrument

The instrument is switched on by turning the rotary switch to

one of the three mode positions, i.e. Ω, A or Fn. The Ω

(resistance) and A (AC current) measurements are both auto-

ranging.

Fig 8. Resistance measurement mode

Measuring Resistance Mode

With the resistance (Ω)mode selected simply open the clamp

and clamp around a ground conductor to be measured. The

instrument automatically senses the jaw opening and activates

the open jaw icon ( ) on the display. As soon as the jaw is

closed the open icon is removed and a resistance measurement

is initiated. A reading is taken periodically and the display

updated until the user presses the HOLD key to freeze the

reading or turns off the instrument.

Resistance measurements in high noise environments can be

problematic resulting in no reading. The DET14C / 24C

instruments incorporate a noise symbol ( ) to indicate

presence of noise during a measurement. A filter function

indicated by the filter icon ( ), is activated automatically in the

presence of noise. The filter results in a slightly longer

measurement period but offers improved noise immunity.

Measuring Current Mode

To measure true RMS AC current simply set the rotary switch to

the current mode (A) and clamp around the cable or tape to be

measured. RMS current is displayed on the screen in either A or

mA.

HOLD

The HOLD key can be used to freeze a result in either resistance

or current mode. Once held, the result can be saved to memory

using the save () button.

HOLD has two modes depending on when it is activated:

If a measurement is in progress and HOLD is pressed it

will freeze the result even if the clamp is opened and

removed from the unit under test.

The user may also use the HOLD function with the clamp

closed before a measurement is taken. This mode assists

users to take readings in difficult to reach areas where the

instrument display may not be visible during the

measurement. Depressing the HOLD button for two

seconds with the clamp closed and no conductor present

will activate an automatic hold of the next result. HOLD

will flash on screen until the measurement is taken or it

times out. The instrument will sense open jaws, closed

jaws and take a reading, then freeze the reading on

screen and beep to indicate that the measurement is

complete.

Backlight

A low intensity backlight is provided on the instrument display to

facilitate measurements in dark conditions. The backlight button

( ) toggles the backlight on and off. An auto off timer will

switch the backlight off after 20 seconds to conserve power.

Saving Data

Data is saved in either resistance mode (Ω) or current mode (A).

Pressing the save key () will record a result with a time and

date stamp. It is important to regularly ensure that the time and

date settings are correct. Time and date are set from the

Function mode (Fn).

Function Mode

The Function mode (Fn) contains five minor functions on the

instrument:

Recall records ( )

Delete records ( )

Download via IrDA-to-USB ( )

Alarm setting ( )

Set Time/Date (H:M:S/D:M:Y M:D:Y Y:M:D )

In Function mode (Fn) the buttons shown in Figure 7 operate as

arrow buttons and are depicted in green matching the green

(Fn) icon on the rotary switch. The right arrow button is used to

scroll through minor functions in the order listed.

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