Chauvin Arnoux 6250 User manual

ENGLISH User’s manual
C.A 6250
MICROHMMETER

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Thank you for purchasing a C.A 6250 microhmmeter.
To obtain the best service from your instrument:
read this user manual carefully,
comply with the precautions for use.
WARNING, risk of DANGER! The operator must refer to this user’s manual whenever this danger symbol appears.
Equipment protected by double insulation.
Earth.
The CE marking indicates conformity with European directives, in particular LVD and EMC.
The rubbish bin with a line through it indicates that, in the European Union, the product must undergo selective
disposal in compliance with Directive WEEE 2002/96/EC. This equipment must not be treated as household waste.
Definition of measurement categories:
Measurement category IV corresponds to measurements taken at the source of low-voltage installations.
Example: power feeders, counters and protection devices.
Measurement category III corresponds to measurements on building installations.
Example: distribution panel, circuit-breakers, machines or fixed industrial devices.
Measurement category II corresponds to measurements taken on circuits directly connected to low-voltage installations.
Example: power supply to electro-domestic devices and portable to.
PRECAUTIONS FOR USE
This device is compliant with safety standard IEC 61010-2-030 and the leads are compliant with IEC 61010-031, for voltages up
to 50 V with respect to earth in category III.
Failure to observe the safety instructions may result in electric shock, fire, explosion, and destruction of the instrument and of
the installations.
The operator and/or the responsible authority must carefully read and clearly understand the various precautions to be taken
in use. Sound knowledge and a keen awareness of electrical hazards are essential when using this instrument.
If you use this instrument other than as specified, the protection it provides may be compromised, thereby endangering you.
Before making any measurement, check that the resistance to be checked is not live: never connect the instrument to a
live circuit.
Do not use the instrument if it seems to be damaged, incomplete, or poorly closed.
Use only the accessories supplied with the instrument, compliant with safety standards.
Before each use, check the condition of the insulation on the leads, housing, and accessories. Any item of which the insulation
is deteriorated (even partially) must be set aside for repair or scrapping;
When resistances having a large inductive component (motors, transformers, etc.) are measured, the instrument automatically
discharges the inductance after the measurement. During this discharging, the symbol is displayed.
Do not disconnect the measuring cords until the symbol disappears.
Comply with the charging characteristics of the battery and use a fuse of the appropriate type and rating; failure to do so
may damage the instrument and void the warranty.
Set the switch to OFF when the instrument is not in use.
Check that none of the terminals is connected and that the switch is set to OFF before opening the instrument.
All troubleshooting and metrological checks must be performed by competent and accredited personnel.

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CONTENTS
1. PRESENTATION....................................................................................................................................................................... 4
2. DESCRIPTION.......................................................................................................................................................................... 5
2.1. FRONT PANEL OF THE C.A 6250.................................................................................................................................. 5
2.2. KEYS .............................................................................................................................................................................. 5
2.3. DISPLAY UNIT................................................................................................................................................................ 6
2.4. RS 232 INTERFACE: CHARACTERISTICS..................................................................................................................... 7
3. USE / PROCEDURE................................................................................................................................................................. 7
3.1. MAKING A MEASUREMENT.......................................................................................................................................... 7
3.2. SELECTION OF THE MEASUREMENT MODE : KEY ......................................................................... 8
3.4. ACTIVATING THE ALARMS.......................................................................................................................................... 10
3.5. STORING AND RETRIEVING MEASUREMENTS (MEM / MR)..................................................................................... 11
3.6. INSTRUMENT CONFIGURATION : SET-UP ................................................................................................................. 12
3.7. PRINTING RESULTS (PRINT/PRINT MEM) .................................................................................................................. 13
3.8. LIST OF CODED ERRORS ........................................................................................................................................... 14
4. CHARACTERISTICS .............................................................................................................................................................. 15
4.1 CHARACTERISTICS...................................................................................................................................................... 15
4.2. POWER SUPPLY.......................................................................................................................................................... 15
4.3. ENVIRONMENTAL CONDITIONS................................................................................................................................. 16
4.4. PHYSICAL CHARACTERISTICS .................................................................................................................................. 16
4.5. COMPLIANCE WITH INTERNATIONAL STANDARDS.................................................................................................. 16
5. MAINTENANCE...................................................................................................................................................................... 16
5.1. SERVICING................................................................................................................................................................... 16
5.2. MAINTENANCE ............................................................................................................................................................ 17
6. WARRANTY............................................................................................................................................................................ 19
7. TO ORDER.............................................................................................................................................................................. 20

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1. PRESENTATION
The C.A 6250 microhmmeter is a top-quality portable digital measuring instrument with backlit LCD display. It is designed to
measure very small resistances.
Housed in a rugged construction-site type case with cover, the C.A 6250 is a self-contained instrument powered by a rechargeable
battery with built-in charger.
It provides 7 measurement ranges, from 5 mW to 2,500 W, that can be accessed and selected directly on the front-panel rotary
switch.
It uses the 4-wire measurement method (see 3.1.1), with automatic compensation of spurious voltages.
It has many advantages:
- automatic detection of the presence of an external AC or DC voltage on the terminals, before or during the measurement,
which disables or stops the measurements when measurement accuracy is no longer guaranteed,
- 3 different measurement modes depending on the nature of the resistance to be measured,
- protection of the operator when a resistance having a large inductive component (motor, transformer, etc.) is measured.
After the measurement, the instrument automatically discharges the inductance if the measuring cords are left connected
to the inductive resistance measured.
- programming of alarm thresholds (alarms in the form of audible beeps),
- possibility of measuring the measurement temperature using a Pt100 jack on the front panel,
- function for automatic calculation of the resistance at a reference temperature using the possibility of selecting the
type of metal the resistance is made of and its temperature coefficient,
- extended memory making it possible to store approximately 1,500 measurements,
- indication of the level of memory use,
- indication of battery charge condition,
- automatic switching of the backlighting to standby to save battery power,
- RS 232 interface to print the results on a serial printer or export them to a PC.
Its main applications are:
bonding measurements,
earth continuity measurements,
motor and transformer resistance measurements,
contact resistance measurements,
component measurements,
electric cable resistance measurements,
tests of mechanical links.

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2. DESCRIPTION
2.1. FRONT PANEL OF THE C.A 6250
4 4mm-dia. safety terminals identified as C1, P1, P2 and C2
9-way rotary switch:
- Off : instrument power off / setting for charging
- 2500 W: 2500,0 Wrange – measuring current 1 mA
- 250 W: 250,00 Wrange – measuring current 10 mA
- 25 W: 25,000 Wrange – measuring current 100 mA
- 2500 mW: 2500,0 mWrange – measuring current 1 A
- 250 mW: 250,00 mWrange – measuring current 10 A
- 25 mW: 25,000 mWrange – measuring current 10 A
- 5 mW: 5,0000 mWrange – measuring current 10 A
- SET-UP : instrument configuration
1 yellow START/STOP key: start/stop measurement
8 elastomer keys each having a primary function and a secondary function.
1 backlit LCD screen
1 receptacle for connection to line power to charge the battery
1 jack for connection of a Pt100 temperature probe,
1 RS 232 serial INTERFACE plug (9 pin contacts) for connection to a PC or to a printer.
2.2. KEYS
8 keys each having a primary function and a secondary function:
2nd Activate the secondary function written in yellow italics bellow each key. The symbol appears on the screen.
/
METAL
Primary function: before starting the measurement, select the desired measurement mode : inductive, non-
inductive or non-inductive with automatic triggering.
Secondary function: select the metal for the temperature compensation calculation:
Cu, Al, or Other metal.
R ( q )
ALARM
Primary function: activate/deactivate the temperature compensation function: calculation of the resistance
at a temperature other than the measurement temperature.
Secondary function: activate/deactivate alarms. The direction and the triggering value (high or low) are
adjusted in the SET-UP menu.
MEM
MR
Primary function: store the measurement at an address identified by an object number (OBJ) and a test
number (TEST).
Secondary function: retrieve stored data (this function is independent of the setting of the switch) except in
the OFF and SET-UP settings.
%
&
Primary function: in SET-UP mode, select a function or increment a flashing parameter.
Secondary function: in SET-UP mode, select a function or decrement a flashing parameter.

n
Primary function: select the parameter to be modified (in wraparound mode, from left to right). In SET-UP
mode, access the adjustments of a function.
Secondary function: in SET-UP mode, shift the decimal point and select the unit.
PRINT
PRINT MEM
Primary function: print the measurement directly to a serial printer.
Secondary function: print stored data to a serial printer.
]
Primary function: activate/deactivate the backlighting of the display unit.
Secondary function: activate and adjust the sound level/deactivate the audible signal.

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2.3. DISPLAY UNIT
Dual liquid crystal display.
Secondary display unit: measurement parameters / memory address
Main display unit: measured values
Other indications and symbols:
1. indicates that the buzzer/audible signal is activated
2. indicates the battery charge condition
3. indicates that temperature compensation is activated
4. indicates the metal selected for the temperature compensation function
5. indicates that data are being transmitted to the serial interface
6. Indicates the memory use level
7. PRINT: printing of current measurement
PRINT MEM: printing of stored data
MEM: storage of measurement
MR: retrieval and reading of a stored measurement
REMOTE: instrument remotely controlled via the RS 232 interface
8. measurement units of the result displayed
9. indicates the status of the instrument:
OPER: measurement in progress
ST BY: Standby -no measurement in progress - waiting for an action
10. indicates the measurement mode selected
11. indicates the range and measuring current selected
12. Warning! Do not disconnect the measuring wires/presence of external voltage
13. indicates that the secondary function of a key will be used
14. indicates which alarm(s) are activated and their direction

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2.4. RS 232 INTERFACE: CHARACTERISTICS
The RS 232 jack can be used with 4 different peripherals (choice of 4 different links in SET-UP) :
- PC : activate RS232 link between the instrument and a computer
- PRNT : activate RS232 link between the instrument and a printer
- TRIG : activate the remote measurement triggering function
- VT100 : activate RS232 link between the instrument and a disply console
Note that the RS232 can be switched OFF to deactivate the input and output functions of the connector (saves battery power).
Selecting an RS232 link opens a submenu in which to choose the data rate between the instrument and the peripheral. This
adjustment is made in SET-UP (see § 3.6)
The baud rate can be set to 4,800, 9,600, 19,200, or 31,250.
Data format: 8 data bits, no parity, 1 stop bit, hardware control (CTS).
3. USE / PROCEDURE
3.1. MAKING A MEASUREMENT
3.1.1. CONNECTIONS
Connections are made in accordance with the 4-wire measurement principale; the set-up used is shown in the figure bellow:
Where :
Ri = Internal resistance of the instrument.
Rf = Resistance of the measuring wires.
Rc = Contact resistance.
Rx = Resistance to be measured.
From a DC voltage U, a generator delivers a current I.
A voltmeter measures the voltage drop Ux on the terminals of the resistance Rx to be measured and displays Rx = Ux/I.
The result is independent of the other resistances in the current loop (Ri, Rf, Rc) provided that the total voltage drop they cause,
in combination with Rx, is less than the voltage the source can deliver U (U ≤6V).
3.1.2. SEQUENCE OF USE
1. Turn the rotary switch from OFF to the desired range. The range and the associated measuring current are then indicated at
bottom left in the display unit.
2. Press the key until the desired measurement mode is obtained.
For a detailed description of the different measurement modes, see § 3.2.
3. If desired, press the R(q)key to activate the temperature compensation function. For a detailed description of this function,
see § 3.3.
4. If desired, press the ALARM ( + R(q)) key to activate the alarm(s).
5. Connect the measuring cords to the instrument, then to the resistance to be measured.
6. The instrument indicates ST BY (standby). Press START to start the measurement and, if applicable, STOP to stop it (this
depends on the measurement mode selected).
Remark: Changing ranges during a measurement stops the measurement cycle; the instrument returns to standby (ST BY).
7. The instrument displays the measurement result.
8. Then press MEM to store the result and validate by pressing again.
For a detailed description of result storage, see § 3.5.

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3.2. SELECTION OF THE MEASUREMENT MODE : KEY
There are three measurement modes:
- Inductive resistance measurement:
- Non-inductive resistance measurement:
- Non-inductive resistance measurement with automatic triggering: AUTO
The measurement mode is selected by successive presses on the key; the mode selected is displayed bellow, in the
centre of the display unit.
3.2.1. MEASUREMENT IN INDUCTIVE RESISTANCE MODE
This mode is used for measurements on transformers, motors and other inductive devices.
The measurement is started by pressing START and stopped by pressing STOP.
Description:
- press the START key.
- automatic check of connection of the “current” and “voltage” wires: if the connection is incorrect, an error message is
displayed (Err 11 if the “current” wires are incorrectly connected, Err 12 if the “voltage” wires are incorrectly connected);
the instrument switches to standby; the cycle is resumed when the connection is correct.
- current not established, measurement of residual voltage Uo on the terminals of the resistance. If this voltage is too high,
the instrument displays Err 13.
- establishment of current I, maintained for as long as the instrument does not return to “standby”.
- measurement of voltage U1 on the terminals of the resistance and display of the measurement R = (U1 - Uo) / I.
- any subsequent measurement involves the measurement of Un only, since Uo is kept in memory the cycle is ended by
pressing the STOP key.
Operating diagram:
C = check of connections
0 = measurement of residual voltage (stored).
1, 2, 3 ... n = successive measurements of the voltage on the terminals of the resistance (interval between two measurements:
120 ms).
The delay stated for the first measurement (1,200 ms) is an indication only; it can vary according to the load measured.
Remarks :
If the range is exceeded, the instrument displays Err 07.
The source of current is protected against overheating. If a measurement at 10 A lasts too long (> several tens of seconds)
and causes a temperature rise, the current is cut off and the instrument displays Err 05. The instrument must be allowed to
cool down before another measurement can be made.
After a measurement cycle, the instrument automatically discharges the inductance completely.
During this discharging, the instrument displays the following icon:
Never touch or disconnect the leads before the icon disappears.

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3.2.2. MEASUREMENT IN NON-INDUCTIVE RESISTANCE MODE
This mode is used to measure contact resistances, bondings, and, generally, any resistance having a time constant shorter than
a few milliseconds.
The measurement is started by pressing START and stops automatically as soon as the measurement result is available.
START must be pressed again to make another measurement.
Description :
- press the START key.
- automatic check of connection of the “current” and “voltage” wires: if the connection is incorrect, an error message is
displayed (Err 11 if the “current” wires are incorrectly connected, Err 12 if the “voltage” wires are incorrectly connected);
the instrument switches to standby; the cycle is resumed when the connection is correct.
- current not established, measurement of residual voltage Uo on the terminals of the resistance. If this voltage is too high,
the instrument displays Err 13.
- establishment of current I.
- measurement of the voltage on the terminals of the resistance U1 then cutoff of the current.
- display of the measurement R = (U1 - Uo) / I
- automatic stop at the end of the measurement. The instrument, in standby, is ready for another measurement.
Operating diagram (Example : two measurements cycles):
C = check of connections
0 = measurement of the residual voltage.
M = measurement of the voltage on the terminals of the resistance.
Remarks :
If the range is exceeded, the instrument displays Err 07.
This mode has many advantages:
- it reduces the consumption, because the current is cut off between measurements, and so increases the battery life,
- it avoids a temperature rise in the resistance measured,
- It improves the compensation of spurious electromotive forces (because they are measured and compensated before each
resistance measurement).
3.2.3. MEASUREMENT IN NON-INDUCTIVE RESISTANCE MODE WITH AUTOMATIC TRIGGERING
This mode is intended only for measuring resistances without time constants.
In this measurement mode, there is no need to press START (other than to start the whole measurement process) or STOP
to start or stop the measurement.
The measurement is triggered automatically as soon as the current and voltage circuits are established (as soon as
contact is established) and stops automatically as soon as the measurement result is available.
Another measurement is started automatically as soon as the current and voltage circuits are established again (as soon as
contact is established again), etc.
Description :
- press the START key to activate the cycle.
- connect the wires to the resistance. The instrument remains on standby until the links are established.
- measurement of residual voltage Uo on the terminals of the resistance.
- establishment of measuring current I, measurement of the voltage U1 on the terminals of the resistance, and display of
the measurement R = (U1-U0)/I
- to make another measurement, it is necessary to release at least one link, then reestablish it.
- cycle ended by pressing the STOP key
Remarks :
If the range is exceeded, the instrument displays Err 07.

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3.3. TEMPERATURE COMPENSATION: (q)
3.3.1. PRINCIPLE
The metals used for the windings of certain components (e.g. the copper in transformers and motors) have large temperature
coefficients (of the order of 0.4 %/°C for copper and aluminium).
This makes resistance measurements strongly dependent on the temperature of the component.
The “temperature compensation” function is used to adjust the resistance measured, which depends on the ambient temperature
(measured or programmed), to the value it would have at a programmed reference temperature.
The “temperature-compensated” resistance is calculated as follows:
R(t°ref)= R(t°amb) * (1 + (alpha * t°ref ) )
1 + (alpha * t°amb)
where
R(t°amb) : resistance measured at ambient temperature by the instrument
t°amb : temperature measured by a PT100 or programmed by the user
Alpha : temperature coefficient of the selected metal (Aluminium, Copper or»Other metal»)
t°ref : programmed reference temperature to which the measurement is referred
t°amb , alpha and t°ref are parameters that can be programmed in SET-UP (see § 3.6.).
Various values of temperature coefficient:
Metal per °C Metal per °C
Aluminium 0,00403 Lead 0,0043
Copper 0,00393 Mercury 0,00090
Carbon (0-1850°C) 0,00025 Platinium 0,0038
Iron 0,0050 Zinc 0,0037
3.3.2. PROCEDURE
first check the programming of the t°amb, alpha, and t°ref parameters (see § 3.6.) and the connections.
press the R(q) key
- the R(q) symbol and the metal selected are displayed steadily on the display unit.
- the small display unit indicates the temperature t°ref then the temperature t°amb.
once the measurement has been made, the instrument displays:
- on the small display unit, depending on the programming:
the programming ambiente temperature
or the temperature measured by the temperature sensor
or «-.-.-.-» if the temperature sensor is validated but not connected or incorrectly connected,
or if the temperature measured is out of bounds (-10°C to 55°C).
- on the large display unit:
the compensated resistance value
Remark :
Err 10 is displayed if a temperature is out of bounds or if the leads of the sensor become disconnected.
3.4. ACTIVATING THE ALARMS
The alarms are activated by successive presses on the MR key ( + R(q)).
The instrument displays:
alarm 1 and its direction of activation.
then alarm 2 and its direction of activation.
then alarm 1 and alarm 2 and their directions of activation.
The values of the alarms and their direction of activation are programmed in advance by the user in SET-UP (see § 3.6)