ASCEL Electronic AE20218 Montage- und Bedienungsanleitung

Æ20218

Milliohm Meter

Assembly and

Operation Manual

REV 3.0 DE

Table of Contents

Safety Information.....................................................................ii

Handover of a Device Built From a Kit....................................iv

Intended Use.............................................................................iv

ESD Warning.............................................................................v

AE2 218 Milliohm Meter..........................................................1

Circuit Description.....................................................................2

Four Wire (Kelvin) Measurement..............................................3

Soldering....................................................................................5

Component Reference................................................................7

Assembly..................................................................................15

Adjustment...............................................................................18

Troubleshooting Checklist.......................................................2

Power Supply...........................................................................22

Case Mounting.........................................................................23

Operation..................................................................................24

Circuit Diagram.......................................................................28

Bill of Materials.......................................................................3

Component Placement Diagram..............................................33

Data Interface...........................................................................34

Specifications...........................................................................37

Warning

Please read this manual before you assemble and use this it.

Keep it accessible for all users at all times.

Safety Information

Know and follow the applicable regulations for

electric devices in your region. In Germany,

these are especially VDE 0100, VDE

0550/0551, VDE 0700, VDE 0711 and VDE

0860. Pay attention to the following safety

advices:

• Disconnect the power supply before opening the case.

• Wor on devices only if you made sure that they are

disconnected from any power supply, and any possible charge

inside is discharged.

• Devices must only be used if they are mounted in a case in a

way that prevents the user from touching any live wires or

parts. Disconnect the device from its power supply during

assembly.

• Always chec the power cords for brea s or damaged

insulation. Replace any defective parts immediately.

• See advice from a qualified expert if you are not sure about

any specific value of a part, an installation procedure, or how

to connect accessories.

•Always chec if the device is suitable for the intended purpose

before putting the unit in use. See assistance from a qualified

professional or the manufacturer if you are not sure.

• The manufacturer assumes no liability for errors made during

assembly or operation.

• Devices that need a supply voltage greater that 24V may be

assembled by professionals only, to avoid hazards from

improper assembly.

• In schools, educational institutes or wor shops, the use of this

unit must ta e place under the supervision of qualified staff.

• Do not put this unit in use in an environment where the ris of

fire or explosion or explosive gas, vapor or dust is present.

• If the unit must be repaired, use original parts only. The use of

inappropriate parts may lead to a safety ris .

• Avoid wor ing alone.

• Keep electronic parts away from children.

• Do not replace parts with such that does not meet the required

parameters. For example: never replace a fuse with another one

with higher nominal current!

• Other regulations may apply. Please chec the local safety

regulations for assembling electronic devices.

iii

Handover of a Devi e Built From a Kit

(in countries where applicable)

If you hand over a device built from a it, you legally become

the manufacturer. This mean you are responsible for complying

with the appropriate regulations for electronic devices. All

accompanying papers, in particular this manual, must also be

passed over. Where necessary (for example in the European

Union) you must also publish your identity to the consignee.

Intended Use

(in countries where applicable)

The intended use of this device is measuring resistance within

the given limits.

• Other uses are not approved!

ESD Warning

What is ESD?

ESD (Electrostatic Dis-

charge) is the sudden flow

of electricity between two

objects caused by contact

or an electrical short. It

can reach very high voltages of many V. In some cases even

over 100 V!

Causes of ESD

The main cause of ESD events is static electricity. Static

electricity is usually generated through tribocharging, li e

wal ing on a rug, ascending from a fabric seat, removing some

types of plastic pac aging or using non-ESD compliant tools.

Danger of ESD

The high voltage pulse can easily destroy electronic parts. ICs

and FETs are very sensitive to high voltage. Even a short,

single touch may destroy a part!

How do I prevent damage due to ESD?

Always ground yourself while wor ing with electronic parts. A

grounded conducting wrist strap and proper anti-static wor

surface mat will help prevent ESD damage. Also ma e sure

that the soldering iron is grounded and ESD-safe.

Warning symbol for an

electrostatic sensitive device

AE20218 Milliohm Meter

The AE20218 is a Milliohm Meter – a resistance measuring

device that allows for precise measurements down to the

Milliohm range.

The resolution is 0.1 Milliohm in the 24 Ohm range and 1

Milliohm in the 240 Ohm range.

The Four Wire Measurement Technique used (also nown as

Kelvin Measurement) ensures that the resistance of the test

leads/clips does not interfere with the results.

The optional USB interface allows remote control of the device

with the included software. The easy, plain text command

protocol allows simple integration with external tools and

systems. Every single function of the device can be remote

controlled.

All SMD (Surface Mounted Device) components are already

soldered, so the it is also suitable for beginners in electronics.

The comprehensive manual should help answer all questions

that may arise during assembly.

Please read the complete manual (especially if you are not yet

experienced in electronic engineering) before building the it.

Cir uit Des ription

The circuit diagram of the AE20218 can be divided into several

parts, which are described here.

The digital part is based on microcontroller IC1. IC1 controls

all functions, computes the readings, and drives the LCD. The

USB port is handled by the FT230X UART-USB Bridge (IC4).

The two main parts of the circuit are the current source that

provides the test current, and the measurement of the resulting

voltage drop across the DUT using an AD Converter.

The current source is based on the LT3092 (IC5) Precision

Source, to increase its accuracy the LT1634 (IC6) Precision

Voltage Source is used as the reference. With the 0.1%

tolerance resistors and multi-turn trimmers to adjust the test

current, it ma es a very precise current source.

The AD Converter is a MCP3551 (IC2) which feature the high

resolution of 22 Bit.

IC7 is the 2.5V Reference for the AD Converter, it is the

LT1460 Precision Voltage Reference..

The 5V digital supply comes from the linear regulator IC3. D1

protects IC3 from reverse polarity of the input voltage.

Decoupling capacitors are placed next to all ICs. The supply

voltage for the analog circuitry is decoupled by a ferrite bead.

Four Wire (Kelvin) Measurement

The Four Wire (also nown as Kelvin) Measurement Method is

vastly superior to the traditional Two Wire Measurement

Method for small resistance values, as it ignores the test lead

and contact resistance.

With the Two Wire Measurement, the total resistance the meter

can "see" consists of the Device Under Test (DUT), the test

leads and the contact resistance. Since the latter can be in the

ballpar (or even larger) than the DUT, it ma es accurate

measurements difficult.

Assuming the measurement of a 0.2 Ohm resistor - if the test

leads have 0.1 Ohm resistance each (a typical value), the total

resistance will be 0.4 Ohm (not even counting the contact

resistance) - resulting in an unacceptable error of 100%.

With the Four Wire (or Terminal) Method, the test current is

separated from the Voltage Measurements - four wires

/terminals are used, hence the name.

The Voltage Measurement uses different wires than the test

current - these remove the voltage drop caused by it entirely.

The only error that remains is that from the small current

flowing into the Voltmeter - due to its high impedance it is

negligible, as it is many orders of magnitude smaller than the

actual value.

The resistance of the test clips can be ignored in the voltage

measurement (assuming a typical value of < 1Ohm, it is

irrelevant against the input impedance of the Voltmeter in the

MOhm range) and also in the test current path - since the

current is always constant in a branch, the test current over the

DUT will always be the same as set by the current source.

This allows small values to be precisely measured with the

Four Wire Method, ignoring the resistance of the test leads and

the contacts to the DUT.

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