ASCEL Electronic AE20218 Installation and operating instructions

Æ20218
Milliohm Meter
Assembly and
Operation Manual
REV 3.0 DE
© 2018 Ascel Electronic

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
i

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.
ii

•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!
iv

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.
v
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.
1

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.
2

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%.
3

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.
4

Soldering
Please read the following pages if you are not yet experienced
in soldering. Good soldering is a matter of practice! Practice on
old boards until you feel confident before assembling the it.
• The parts are mounted on the silkscreen side of the PCB.
Except parts whose designators ends with an asterisk like
S1*). These are mounted on the other side!
• Do not inhale the fumes from the flux! Wash your hands
after soldering! Wear protective glasses!
• If you use additional flux, ma e sure it is suitable for
electronics use! Non-suitable flux may contain acid which will
damage the traces on the PCB over time.
• Try to solder fast. Heating up for too long may damage the
components and the board.
• Solder wire with a diameter between 0.5-0.75mm (0.02"-
0.03") is most suitable for through-hole components. Lead
solder is easier to use than lead-free solder.
• A clean, non-oxidized tip is essential for good soldering. Use
a wet sponge or a metal wool tip cleaner to regularly clean the
tip. The metal wool cleaners are superior to a wet sponge as
there is no temperature shoc .
5

• When soldering active components (ICs, Transistors,
LEDs...), it is very important to prevent overheating the
components. They should be soldered in no more than about 5
seconds. In addition, it is important not to confuse the polarity!
See the next chapter on individual component types and their
correct orientation.
• To solder:
1. Use the tip of the soldering iron to simultaneously heat
up the PCB and the component leg.
2. Add solder. It should melt around the component leg.
3. Wait a moment. Do not move the part you just soldered
for a few seconds while it is cooling down. Moving it
may cause the solder joint to crac .
4. Then remove the iron. With lead solder, the solder joint
should be glossy.
• After soldering, use side cutters to cut the leads straight above
the solder joint.
• After you are finished, chec all components for correct
placement and orientation. Also, chec for unintentional shorts
on the board. Small solder leftovers may cause shorts which
can damage the board or the components.
• Use isopropyl alcohol (IPA) or a specific PCB cleaner fluid to
remove flux residues. Flux is corrosive and should not remain
on the board.
6

Component Referen e
1 Resistors
To save PCB space, the resistors are mounted standing. To
install:
1. Bend the leads in form and put the
resistor through the corresponding
mounting holes.
2. Bend the leads aside to prevent the
resistor from falling out.
3. Solder it accurately on the bac
side.
4. Cut the remaining leads above the solder joint.
The resistance value is given with colored bands on the
resistor. The code consists of four, five or six bands. With four
bands, the first two are the base value (see table below), the
third is the multiplier to the base value and the fourth is the
tolerance. Five-band code uses the first three bands for base
value. With six bands, the sixth is the temperature coefficient.
The resistor value is:
base value * multiplier [ ± tolerance ]
There are two possible arrangements for the bands order:
7
Type B
Type AType A

Color Codes:
Color Digit Multiplier Tolerance ± in %
None - - 20
Silver - 10-2 10
Gold - 10-1 5
Blac 0 100-
Brown 1 1011
Red 2 1022
Orange 3 103-
Yellow 4 104-
Green 5 1050.5
Blue 6 1060.25
Purple 7 1070.1
Grey 8 1080.05
White 9 109-
2 Capa itors / Ele trolyti Capa itors
Capacitors are soldered the same way as resistors. Electrolytic
capacitors are polar. They must be mounted in the correct
orientation! They will be destroyed when installed in
reverse polarity and may even burst!
Please eep in mind that different manufacturers mar the
polarity in different ways. The mar ing may represent the
positive or the negative terminal! The actual polarity (+ or -) is
printed inside the mar er band that points at one of the leads.
8

Capacitance Identification
A three-digit number without letters is the capacitance in pF,
calculated this way:
a∗10b
where
a
are the first two digits
and
b
is the third digit (105 become 10*105 pF = 1µF). One-
or two-digit numbers states the capacitance directly in pF. A
number including the letter "n" is the capacitance in nF, where
3n9 is 3.9nF.
Upper-case characters denote the tolerance according to this
table:
B C D F G H
±0.1pF ±0.25pF ±0.5pF ±1% ±2% ±2.5%
J K M S Z P
±5% ±10 ±20 +50%
-20%
+ 80%
- 20%
0%
-10%
A number following up indicates the electric strength.
Sometimes you may encounter a number li e 0.5, this is the
capacitance in µF.
Electrolytic capacitors are usually labeled with the capacitance
in µF straight. µ is where the decimal point is: µ33 is 0.33 µF,
3µ3 is 3.3µF and 33µ is 33µF.
9

3 Diodes
The circular band on diodes identifies the cathode (negative
terminal). The bar depicts the cathode in the symbol. The
positive terminal is called the anode.
Diodes are mounted horizontal. Try not to heat up the body of
the diode while soldering.
4 LEDs
LEDs (light-emitting diodes) must be soldered with respect to
the correct polarity as well. The cathode is identified by the
short lead and the larger electrode inside.
1

5 IC-So kets / ICs
With ICs (integrated circuits), it is essential to observe correct
polarity. Most ICs will be damaged or destroyed when mounted
incorrectly. The mar on the sil screen must match the notch
on top of the IC.
Do not use the firmware version stic er on the MPU to
determine the orientation! Only the notch is relevant.
Pin numbers are counted counter-cloc wise, starting from the
notch.
Note: Please also pay attention to the ESD warnings at the
beginning of this manual. ICs are ery ESD sensiti e, they can
be destroyed e en by a minor electrostatic discharge e ent!
11

6 Transistors
Transistors must be mounted in the correct orientation. The flat
side of the transistor must match the correspondent side in the
sil screen drawing. The leads may not cross.
Note: field-effect transistors (FETs) are extremely
sensiti e to ESD.
7 Crystal
The polarity of the crystal is not relevant, but the bottom side
of the pac age is conductive. To prevent shorts, the crystal
should be mounted with a little distance to the board see
the image on the next page).
12

8 Indu tors
Inductors are soldered just li e resistors. They also use similar
color-coding, usually with four bands. The first two are the
base value (see table below), the third is the multiplier to the
base value and the fourth is the tolerance. The inductor value
is:
base value * multiplier [ ± tolerance ]
Color Codes:
Color Digit Multiplier Tolerance ± in %
None - - 20
Silver - 10-2 10
Gold - 10-1 5
Blac 0 100-
Brown 1 1011
Red 2 1022
Orange 3 103-
Yellow 4 104-
Green 5 1050.5
Blue 6 106-
Purple 7 107-
Grey 8 108-
White 9 109-
13

9 Relay
Pin 1 on the Relay is mar ed on the Sil screen on the PCB and
on the Relay itself with a line.
10 4mm Binding Posts
First, remove the plastic rings before soldering the Binding
Posts, as they would melt during soldering otherwise.
Press the Binding Posts through the holes in the PCB and
solder them using more solder than the other parts. Use a large
soldering iron tip and plenty of solder for the Binding Posts as
they need a lot of heat. If your soldering iron's temperature is
adjustable, set the temperature 20–30°C higher than normal.
Try to heat the Binding Posts, not the PCB, as too much heat
may damage the trac s.
14