Amptec Research 620UK-4 User manual

AMPTEC 620UK-4
SAFETY OHMMETER
PHONE [phone]
website http://www.amptec.com
FAX [phone]; TOLL FREE IN THE USA
MAINTENANCE and OPERATION MANUAL
V4 ( 4 Wire Kelvin Version)
Amptec Research Corp.
13231 Rooster Springs Rd.
Austin, TX 78737 USA
T: [phone] // E: [email protected]

TABLE OF CONTENTS
SECTION A: RECEIVING AND INITIAL INSPECTION
A-1Introduction to the AMPTEC 620UK Safety Ohmmeter (p. 4)
A-2Unpacking and Inspection (p. 4)
A-3 DC Battery Power Requirements (type AA) (p. 5)
A-4Setup and Preparation for Use (p. 6)
SECTION B: 620UK EXPLOSIVE SAFETY
OHMMETER SPECIFICATIONS
Table B-2. Specifications (p. 7)
SECTION C: REPLACEMENT AND ACCESSORY
ITEMS
C-1 Available Accessories and Test Leads (p. 8)
SECTION D: OPERATION, FUNCTION AND USE
D-1 General Use (p. 9)
D-2 Front Panel (p.9)
D-2.1 Test Leads and Chassis Ground Connector (p. 9)
D-2.2 Main Power Switch (p. 10)
D-2.3 Auto “TurnOff” (p. 10)
D-2.4 Light (p. 10)
D-2.5 Resistance Range Selection (p.10)
D-2.6 Zero Operation (p. 11)
D-3 Photo of 620UK Ohmmeter with carrying case (p.13)
D-4 620UK Metal Chassis Description (p. 14)
2

SECTION E: MAINTENANCE, REPAIR, AND
CALIBRATION
E-1 General (p. 15)
E-2 Troubleshooting only by Authorised Personnel (p. 15)
E-3 Circuit Board Operation Overview (p. 15)
E-4 Ohmmeter Assemby/Dissasembly Diagram (p.16)
E-5 Block Diagram and Circuit Description (p. 17)
E-5.1 Principle of Operation
E-6 Trouble-shooting or Diagnostic Test Procedure for AMPTEC 620UK
Ohmmeter Printed Circuit Board (p.18)
E-6.1 Current Source PCB Diagnostic Routine (p. 18)
E-6.2 DVM PCB Diagnostic Routine (p. 18)
E-7 PCB Replacement Procedure (p.19)
E-8 620UK Calibration Adjustment Procedure (p.19)
E-9 Battery Compartment Design and Description (p.19)
E-10 Low Battery Indicator (p. 21)
E-11 620UK Rear Panel Diagram (stickers) (p.21)
ANNEX: INSTRUCTIONS SPECIFIC TO HAZARDOUS AREA USAGE (P. 22)
3

A-1. Introduction - AMPTEC 620UK
The AMPTEC 630, 640 and now the AMPTEC 620 Series Failsafe Ohmmeters have become the standard in the
Safety Ohmmeter/Igniter Circuit Test industry. They provide extremely safe and reliable resistance testing of
explosive or volatile devices. Safety Approvals from various Safety Boards include, the U.S. Air Force 620A-4 for
generic use on munitions and the 620UK by an independent European Eex
certifying body for Intrinsic Safety. The United Kingdom Ministry of Defense (UK MOD) and other versions also
have approved the 620UK Bonding Ohmmeter. Devices the AMPTEC 620UK Safety Bonding Ohmmeter may be
used on include: 1) chassis ground connections on fighter jets in Explosive and Volatile environments, 2) fuses,
3)squibs, 4) igniters, 5) explosive bolts, 6) rocket motor squibs, 7) flares 8) EED activated mortars, 9) EED activated
shells, 10) EED activated rounds and many others .
The
AMPTEC 620UK is approved by SIRA Test & Certification Limited for an intrinsic safety classification of
EEx ib IIC T4 in accordance with the ATEX Directive. SIRA Test & Certification Limited is located in
Chislehurtst, Kent BR7 5EH ENGLAND
A-3)
explosive ordnance and AMPTEC
The AMPTEC 620UK Ohmmeter complies with the EU ATEX
Directive and meets the Intrinsic Safety standard Eex-ib-IIc-T4. The AMPTEC 620UK Ohmmeter has passed
EMC testing in accordance with British Defence Standard 59-41Radiated Emissions and Susceptibility. It is also
complies with British Defence Standards 66-31 (Environmental Heat, Cold, Altitude, Humidity and Atmospheric
Stress tests), as well as British Defense Standard 07-85 and British Defense Standard 05-34. The AMPTEC
620UK Ohmmeter provides a reliable and intrinsically safe means of measuring electrical resistance of aircraft
chassis ground connections, rocket motor squibs, warhead squibs , explosive bridge wire and/on a variety of
devices. Featuring seven resistance ranges and an all metal case with a separate battery compartment, the AMPTEC
620UK provides a safe and easy method of measuring resistance in explosive and volatile atmospheres.
A-2. Unpacking, and Inspection
Should the AMPTEC shipping box appear damaged upon arrival notify the carrier
immediately. If the 620UK appears damaged, the carrier's agent should authorize repairs
before the unit is returned to the factory. Even if the instrument appears undamaged, it
may have suffered internal damage in transit that may not be evident.
R M A
SECTION A - RECEIVING AND INITIAL INSPECTION
4
The AMPTEC 620UK is a 2-wire ( 4 Wire Version Kelvin now available) failsafe digital ohmmeter which reliably
uses very low test currents for its resistance measure-ment. The open circuit voltage on the main “Test Lead”
connector (Pattern 104, 3 way NSN plug) is also diode protected (voltage clamped) and ideal for use in “volatile”
environments. The AMPTEC 620UK Explosive Safety Ohmmeter is voltage limited (diode protected) to prevent
arcing associated with the use of the meter. The field tested Failsafe Output Circuitry pioneered by AMPTEC
RESEARCH ensures that test current levels do not exceed the specified "failsafe current" even in a worst-case
component failure situation. To conserve battery power, the AMPTEC 620UK automatically shuts down, or turns
itself off after approx. 20 minutes of “inactivity”. The AMPTEC 620UK does not need to “warm-up”, so the user
may simply repress the power button to effectively reset the “auto-shutdown” timer. Should the internal batteries (4
ea. AA type) reach a low energy level the “LO BAT” indicator message will appear on the unit’s display. (see
Section

If the unit fails to operate or fails to meet the performance specifications of Section B, notify the carrier's agent
and your nearest AMPTEC Sales Agent’s Office (i.e. see our website at http://www.amptec.com for contact
info). Retain the shipping carton for the carrier's inspection. DO NOT return equipment to AMPTEC
RESEARCH or any of its sales offices without first obtaining an (RMA) Return Material Authorization
number. We need to know who to contact and how to contact (i.e. phone number and FAX number) in order to
properly coordinate the return of the repaired AMPTEC product.
By calling AMPTEC’s service agent first, prior to just returning the 620UK, we can often troubleshoot
(based on the symptoms you describe) and identify the problem over the phone (i.e battery loose in the
battery holder).
A-3. DC Battery Power Requirements
The AMPTEC 620UK Explosive Safety Ohmmeter is powered by an internal battery pack (4 ea AA i.e.
Alkaline type)that is housed in a separate metal box that requires a security screwdriver for removing the
tamper resistant screws. Replacement batteries must be either of the following:
ontact the sale department at AMPTEC
RESEARCH (i.e website http://www.amptec.com) for 620UK Ohmmeter battery replacements if necessary.
Tamper resistant screws secure the battery cover plate in the rear of the 620UK Explosive Safety Ohmmeter.
Calibration Lab personnel have the proper tools to remove the cover plate over the unit’s battery compartment.
The main “Power” switch has two separate modes. The “ON” position supplies internal battery isolated
A new set of “AA”
batteries in the AMPTEC 620UK battery pack is designed to last approximately 1 year, depending upon use.
Duracell Plus Type MN1500,
Eveready Silver Seal type R65 or Eveready Ultra Plus, Silver Seal type R6F4UP, Varta Type 3006, or GP Type
GP15 to maintain the Eex- ib-IIC-T4 Intrinsically Safe Certification. C
Located in upper left hand portion on the LCD display is a “LOW BAT” indicator area. Look for no “LOW
BAT” indication prior to operating the AMPTEC 620UK Ohmmeter. The absence of the “LOW BAT”
indication in the LCD display indicates the internal batteries have acceptable power levels.
A-4. Setup and Preparation for Use
The AMPTEC 620UK Explosive Safety Ohmmeter may be setup to operate as soon as power is "turned ON"
(requires pressing and holding down power switch for 2 seconds). A quick check for no sign of the "low
battery indicator" a test lead integrity check and/or test lead zero adjustment (see below) and it should be ready
to use.
Consequently, it may be used in any area where the environment does not exceed the specifications of Table B-
2. Avoid exposing the AMPTEC 620UK Ohmmeter to extremes of temperature which will affect accuracy and
shorten battery life-span where possible.
5
power
to operate the AMPTEC 620UK Ohmmeter. If you turn on the AMPTEC 620UK Ohmmeter, and the LCD
display does not come on, it may indicate the batteries are dead and may need replacement by authorized
service personnel. To conserve internal battery power, the AMPTEC 620UK Ohmmeter turns off
automatically after approx. 20 minutes. Simply press the power switch to turn to turn the instrument back
“On or Off”.

The AMPTEC 620UK Explosive Safety Ohmmeter is “4-Wire” Kelvin version ohmmeter.
See diagram below.
6
A-5.1 Principle of Operation
The AMPTEC 620UK Safety Ohmmeter fundamentally uses the familiar principle of "Ohm's Law". It outputs
a constant DC current through a unknown resistance. The DC voltage drop across it is measured and it displays it
(voltage drop) as resistance. The unit’s 2.0 Ohm range outputs an intrinsically safe 5mA level of test current. When
the AMPTEC 620UK outputs 5mA through a 1.0 Ohm resister you should measure a 5mV drop. When you put that
voltage drop into the x10 (times ten) amplifier (only on the 2.0 Ohm range) it becomes 50mV, which inputs into the
DVM PCB and ratiometrically displays the measurement as 1.0000 Ohm. The unit’s 20 Ohm range outputs the
same constant 5mA level (without the x10 amp). When this constant 5.0 mA level is put through a 10.0 ohm
resister, you get a 50mV drop, which inputs into the DVM PCB and is displayed as 10.000 Ohms. The 200 Ohm
range outputs a constant 500uA DC current. When this current level (500uA ) is routed across a 100 Ohm resistor
you get a 50mV drop, which routes into the DVM PCB and is displayed as 100.00 Ohms. As the 620UK selected
range resistance goes up by a factor of 10 the constant DC current level goes down by a factor of 10 keeping the
voltage at 50mV.
4-Wire Kelvin Connections - The V4 version should not use the front panel zero pot (only used with the 2 wire
version) - It is best to keep it (zero pot) turned in the full clockwise position. Connections are made to the front
panel terminals using a 4-wire (Vhigh, Ihigh, Vlow and Ilow) configuration. Proper 4 Wire Kelvin connections
automatically eliminate test lead wire (length) resistance and test lead connection contact resistance offsets (which
is what the zero pot does for 2 wire users). The notched connector end plugs directly into the single access notched
main connector. Turn the connector clockwise until you feel the notch or click of the mating connector of the
620UK. They have the 4 wire current high, current low as well as the voltage sense high and voltage
sense low routed to the end of the leads. The 4 wires (Kelvin config.) then terminate depending on the style with
either a 4 banana jacks or a set of double tipped handheld probes. The 620UK keyed single access connector
also make it extremely difficult if not virtually impossible during normal operation to mis-connect measurement
leads to the 620UK v4 version.
* contact resistance
RESUSTANCE
UNDER TEST
LEAD RESISTANCE
*
*
LEAD RESISTANCE
DC CURRENT
LIMITED
CONSTANT
CURRENT
SOURCE
FAIL SAFE
OHMMETER
VOLTAGE
LIMITING
RESISTOR
4.8 VDC BATTERY
T
N
L
E
O
R
O
R
P
U
C
DVM
( V4 Users only) Disregard the unit's front panel “ZERO” knob. It was only intended for the 2 Wire ohm
version of the AMPTEC 620UK Ohmmeter. It should not be used with the 4 Wire Kelvin ( V4) Version. The
front panel "zero" knob should always be turned all the way to the far clockwise position. For the 2 Wire
NATO connector 620UK users the zero pot allows them to "zero out" a certain amount of "in-series" the test
lead resistance. The 4 Wire Kelvin ( V4) version automatically compensates for this effect -That is proper
4 Wire Kelvin connections automatically eliminate test lead wire (length) resistance and test lead connection
contact resistance offsets (which is what the zero pot does for 2 wire users)

SECTION B - 620UK EXPLOSIVE SAFETY
OHMMETER - SPECIFICATIONS
___________________________________________________
* Actual fail-safe currents vary with each instrument and may be ±20% from the typical value.
Table B-2. Specifications
Accuracy: (for 1 year @25°C ± 10°C)
2.0 ohm range . . . . . . . . . . . . . . . . . . . . . . . . ± 0.02% of reading ± 0.05% of range
20 ohm range thru 20K ohm ranges . . . . . . . . . . ± 0.02% of reading ± 0.02% of range
200K ohm range . . . . . . . . . . . . . . . . . . . . . . ± 0.05% of reading ± 0.05% of range
2.0M ohm range . . . . . . . . . . . . . . . . . . . . . . . . . ± 1.0% of reading ± 0.2% of range
Temperature Range - Operating . . -20°C to +40°C, Storage . . . . . . . -10°C to 70°C
Temperature Coefficient
2.0 ohm through 20 K ohm ranges . . . . ±0.002% per °C (from 0°C-15°C and 35°C-50°C)
2.0 M ohm range ±0.02% per °C (from 0°C-15°C and 35°C-50°C)
Instrument Display . . (20,000 counts) 4½ digit Liquid Crystal Display (LCD) with a
back light for viewing the 620UK display in dim ambient light conditions.
Low Battery Indication . .The 620UK LCD Displays shows “LOW BAT”
Over-Range Indication . . . “ i and blank digits ” in the 620UK LCD display
Measurement Update Rate. . . . . . . . . . . . . . . . Approximately 3 readings per second
Open Circuit Current Source Compliance Voltage . diode clamped at <1.4 volts
Power . . . . Battery Pack inside separate metal box houses (4 ea "AA") 1.5V Alkaline batteries,
requires tamper-proof security screwdriver
Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.0" W x 8 " D x 2.5" H
Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 lbs net; 16 lbs shipping
Calibration Access . . . . requires tamper-proof security screwdriver
: use only Duracell Plus Type MN1500, or Eveready Silver
Seal type R65 or Eveready Ultras Plus, Silver Seal type R6F4UP, Varta Type 3006, or GP Type GP15
620UK Resistance Range/Resolution Nominal Test Current/Fail-Safe Current
7

SECTION C: REPLACEMENT & ACCESSORY ITEMS
Contact the sales dept. at AMPTEC RESEARCH for AMPTEC 620UK (V4)
compatible test leads and accessories.
The AMPTEC 620UK Explosive Safety Ohmmeter is available with a transit case (OP-101) with shoulder strap
and front panel NSN connector compatible multi-function test lead set .
Option “620UK-101” Transit case with anti-static conductive coating - The case houses the
AMPTEC 620UK Ohmmeter with alligator clip test lead set.
Option “620UK-290” Alligator Clip Test Lead
Set (48” long) - ideal for connecting to wires,
some jacks and most exposed posts.
Option “620UK-401” Handheld Probe Test
Lead Set ideal for probing recessed socket
wiring, and flat surfaces (i.e. flares, squib
contacts, and primers).
Option “620UK-201”
Security Screwdriver (snake-eye type) for calibration
maintenance personnel to have access to the unit's battery
compartment and internal electronics. Optionally available upon
request, along with snake-eye security screws provide additional
tamper resistance from unauthorized personnel.
8

D-2.1 Test Leads and Chassis Ground Connections ( 2 wire version only)
The Amptec 620UK Explosive Safety Ohmmeter Test Lead Connection uses a 3-pin connector on its
front panel, labeled “Test Leads” . The output connector is a pattern 104, 3 way Type SB104-T4-BS-
3PXO Nato Stock Number 5935-99-0131244. The pin A of the connector is the Voltage Low and
Current Low Test Lead connection contact. Pin B of the Test Lead connector is Voltage High and
Current High. The third pin (pin C) is chassis ground and/or can be used as a “shield” around the other
two lines (A and B) if your test lead wiring is fitted with a shield wire. When first arriving at a
location, the AMPTEC 620UK user should connect the unit's chassis ground panel jack on the transit
case to a local earthy or ground connection. The unit's chassis ground panel jack is wired to the case,
front panel, rear panel, battery compartment and also Pin “C” of the connector. The unit's chassis
ground can also be plugged into an earth ground connection for example at the test site to preclude any
static voltages from building up.
The AMPTEC 620UK Ohmmeter front panel chassis ground panel jack and pin C of the NATO test
lead connector are both chassis ground. The AMPTEC 620UK user may use either chassis ground
connection as a test lead shield (provided the test leads are the shielded variety). The unit's chassis
ground can also be plugged into an earth ground connection for example at the test site to preclude any
static voltages from building up.
D-1 GENERAL USE
The AMPTEC 620UK is designed to operate for approximately 1 year under normal use before the 4
“AA” batteries need to be replaced. The “LOW BAT” indicator on the units LCD Display is factory
adjusted to come on with the internal batteries need to be replaced. (Due to tamper-proof screw access to
the separate metal battery compart-ment, located in the back of the 620UK, please refer to battery
replacement to authorized CALIBRATION/MAINTENANCE personnel only.). The AMPTEC 620UK is
DC current based, about 200 times more accurate (~0.02%) than AC current models and provide a solid
reading rate of 3 readings per second. The AMPTEC 620UK also uses internal solid state voltage
reference(s) that permit the product to be used immediately after the unit has been turned on (within the
temperature range limits of use as stated in section B of this manual).
D-2 FRONT PANEL
9
SECTION D : OPERATION , FUNCTION, AND USE

D-2.3 Auto “TURNOFF” (Automatic Shutdown)
D-2.4 Light (Front Panel button)
The AMPTEC 620UK Ohmmeter has an LCD Display light switch to turn LCD display lights. If the 620UK
Ohmmeter user is in a dim/poor ambient light environment and viewing the LCD display is difficult press and
hold the front panel switch labeled “LIGHT”. The 620UK Ohmmeter LCD display will be lit and viewable in
dim or dark ambient light conditions, as long as the user holds down the “LIGHT” button (assuming good
batteries). If you press the Amptec 620UK ohmmeter front panel “LIGHT” switch and the LCD display light
does not come on it probably indicates dead batteries or a repair is in order, refer battery replacement or any
repairs to authorised personnel.
D-2.2 Main Power Switch (Front Panel ON/OFF Button)
The main power switch for the AMPTEC 620UK Explosive Safety Ohmmeter is a mo-mentary hold-down
switch that needs to be held down for approx. 2 seconds to turn “ON”. This required momentary “hold
down” routine (for 1 to 2 seconds) helps avoid accidental “Power On” whilst the AMPTEC 620UK Ohmmeter
is riding around inside its carrying case. When first pressed and held, (the power switch ) the instrument should
turn “ON” (i.e. the LCD Digital Display comes on), if the switch is pressed again the unit will turn “OFF”. The
main power switch is covered with a silicon rubber boot to provide added water/dust resistance in harsh
environments.
D-2.5 Resistance Range Selection
The AMPTEC RESEARCH 620UK Explosive Safety ohmmeter is fitted with seven resistance ranges. The
lowest resistance range ( 2.0 Ohm ) provides resistance measurement capability from zero ohms up to the level
of i.9999 Ohms Fullscale. The AMPTEC 620UK resistance range is selected by rotating the front panel
resistance range selection knob to the desired resistance range. The AMPTEC 620UK Explosive Safety
Ohmmeter resistance range selection continues in decades from 2.0 ohms, 20 Ohms, 200 Ohms, 2.0 K Ohms,
20 K Ohms, 200 K Ohms, 2.0 Megohms. If the level of resistance to be measured is not known the AMPTEC
620UK user should select the highest range (2.0 MegOhm Range) and continue down ranging until the user gets
the optimal measurement for the unit’s 4 ½ digit display.
10
The AMPTEC 620UK Explosive Safety Ohmmeter conserves battery power (4 ea. AA batteries - see Section B
for exact type/brand allowed) by turning itself off automatic-ally after 20 minutes of continual use (i.e. without
a change in range). The AMPTEC 620UK Explosive Safety Ohmmeter operator may simply press the main
power (mo-mentary) switch to turn the unit back “ON” for ten more minutes. The operator does not have to
worry about warm-up time associated with turning the unit back “ON” if it automatically goes “OFF” (i.e. into
“Auto Shutdown mode”). The AMPTEC 620UK Safety Ohmmeter operator may also simply make a range
change and return (i.e. either flip the range switch up and back/return or press and temporarily hold the main
power switch on again). This will keep the AMPTEC 620UK ohmmeter operating contin-uously for 10 more
minutes. The benefit of conserving battery power far outweighs the second or two it takes to reset the AMPTEC
620UK's “Power Off” timer.

The AMPTEC 620UK Explosive Safety Ohmmeter Front Panel Test Lead Connection uses pin A of the
connector is the Voltage High, pin B is I (current) High, pin C is Current Low and pin D is Voltage low.
The last pin (Pin E) is chassis ground and/or can be used as a “shield” around the other lines in your test lead
wiring.
Resistance
under
Test
AMPTEC 620UK
Explosive Safety /
Ohmmeter
Test Lead Length Resistance Contact Resistance
Pin A- Wiring
Pin B- Wiring
VHI IHI
VLOW ILOW
D-2.6 Zero (Front Panel Knob) ( * * All V4 - Kelvin version users keep the zero knob far clockwise position)
The AMPTEC 620UK Explosive Safety Ohmmeter externally a “2-Wire” type of ohmmeter.
See diagram below . ( Disregard all references to using the "zero Knob" if you have a V4 Kelvin version)
The AMPTEC 620UK Ohmmeter when measuring resistance - measures the total of : three “in-series” items
as shown above. The first item is the actual test lead wiring resistance coming from pin A (Voltage Low and
Current Low) and pin B (Voltage High and Current High). Test lead resistance depends upon lead length
and gauge of wiring. The second “in-series” item in the resistance measurement loop is the “contact resistance”
of the lead contact when connected to the “resistance under test” (i.e. squib). The third item in the resistance
measurement loop is the “resistance under test” which can be virtually any level or magnitude of electrical
resistance as shown in the diagram above. The AMPTEC 620UK Ohmmeter test lead wiring can be a source of
measurement
Pin A= V High
AMPTEC 620UK Front Panel Test Connector
( V4 version shown)
Pin B= I High
Pin D= V Low
Pin E= Chassis Ground (shield)
11
Pin C= I Low

error or offset, if not compensated for. The front panel “ZERO” knob allows the AMPTEC 620UK Safety
Ohmmeter user to zero out most typical test lead resistance. That is - T
or measurements above 2.0 K Ohms and higher, the “zero knob” adjustment isn’t needed and has no effect (as
the level of test lead resistance offset is so very small compared to the higher resistance level of the “resistance
under test”) .
The steps to adjust the “ZERO” knob (up to 10 turns) are as follows: ( disregard for V4 Version)
he zero knob is for “zeroing or nulling
out” the typical 100-150 milliohms worth of test lead wiring resistance and contact resistance offset - which is
determined when the leads are shorted (see below).
F
Repeat: The front panel “zero knob” doesn’t have an effect on the unit’s 2.0K Ohm or higher
ranges.
1. Select the 2.0 Ohm range (by rotating the unit’s range selection switch to the 2.0 Ohm position).
2. With the NATO pattern 104 compatible test leads connected to the AMPTEC 620UK Ohmmeter, connect or
short the leads at the end together . For example - if they are alligator clip (option 620UK-290) or banana jack
ends (option 620UK-401), connect or short the ends to each other.
3. Adjust the ten turn ( precision potentiometer) zero knob until the AMPTEC 620UK Ohmmeter LCD display
indicates a reading of all zeros (0000 ). Turning the front panel “zero knob” a counter clock-wise direction
compensates by decreasing the resistance offset of the test leads. Turning the zero knob a clock-wise direction
compensates in by increasing (more or higher) resistance offset. If you over-adjust the zero, beyond all zeros
on the display, the negative polarity sign comes on the display indicating a condition of “over-adjustment”.
Simply turn the knob in the clock-wise direction (pos +) until the negative sign in the display disappears . Once
the “ZERO” adjustment of the test leads is accomplished, the AMPTEC 620UK Ohmmeter test leads are ready
to connect to the resistance under test. Once the user has zero’ed the unit’s 2.0 Ohm range, re-zeroing the
AMPTEC 620UK’s other ranges isn’t normally necessary.
AMPTEC 620UK
Explosive Safety /
Ohmmeter
Test Lead Length Resistance
Contact Resistance
Shorted Test Leads
VHI IHI
VLOW ILOW
12

ZERO (continued)
However if the test leads are changed (i.e from clips to probes) we recommend resetting the zero on the
AMPTEC 620UK Ohmmeter.
After the “ZERO” adjustment of the test leads is accomplished, the AMPTEC 620UK Ohmmeter is ready to
connect to the resistance under test. The span of the “zero knob” is not infinite. For ordnance test applications
where the resistance offset of the “squib wire harness”, “a.k.a resistance under test” is greater than the span of
the AMPTEC 620UK Explosive Safety Ohmmeter “Zero” knob most users record the “in-series” offset
resistance. end of zeroing description
D-3 Photo of AMPTEC 620UK in Carry Case
Earth Connection between Case and Ohmmeter is shown
The front panel of the AMPTEC 620UK houses the following components:
A) Pattern 104 3-Way Plug Type SB104-T4-BS-3PXO (NSN 5935-99-0131-244).
B) Chassis Ground Connector.
C) 4½ Digit LCD Display with Low Battery Indicator and Over-Range Indicator.
D) Resistance range selector (Seven way rotary switch with selectable ranges of
2.0 ohm, 20 ohm, 200 ohm, 2.0 K ohm, 20 K ohm, 200 Kohm and 2.0 Mohm).
E) Zeroing Potentiometer to zero the meter reading.
F) Back-Light selector switch to turn backlight on and off.
G) Power on/off switch (hold down for 2 seconds for “Power on”).
13
Item A
Item B
Item C
Item E
Item D
Item F
Item G

D-4 620UK METAL CHASSIS DESCRIPTION
The AMPTEC 620UK Ohmmeter chassis (case) is an aluminum enclosure that also acts as a Faraday cage
surrounding the unit's internal electronics. The Chassis (enclosure) has a front panel earth/ground jack which
enables it to be earthed to the same electrical potential as the equipment which the product will be testing.
Internal AMPTEC 620UK Ohmmeter earthing connects all rear panel, battery compartment, PCBs and front
panel aluminum shield behind the front panel labeling, are connected to the chassis and chassis ground front
panel jack.
In summary, the AMPTEC 620UK Ohmmeter front and rear panels are aluminum shielded and have their
individual chassis ground lug connections electrically wired to the units front panel “chassis” ground front panel
connection.
The chassis is optionally fitted with tamper resistant screws (snake eye type) to ensure that only authorized
access is possible. A special screwdriver is required to gain access to the internal electronics and battery
compartment.
The AMPTEC 620UK Ohmmeter is supplied with a carrying case that is made of a durable water resistant
material coated with a permanent conductive (anti-static) protective layer to prevent electrostatic discharge. An
earth connection is made from the AMPTEC 620UK Ohmmeter to the Carrying Case. This is shown in the
photograph on page 13.
a) b)
14

SECTION E : MAINTENANCE , REPAIR AND CALIBRATION
E-1. General
The AMPTEC RESEARCH 620UK Ohmmeter is shown in PCB block diagram form on page 17.
The AMPTEC 620 Series Igniter Tester uses modern solid-state semiconductors exclusively and digital CMOS
circuits extensively to minimize power requirements and make battery operation useful and practical. AMPTEC
also maintains a 620UK spare PCB inventory and it’s customer service department can also provide
additional assistance in the trouble shooting process.
E-2. Troubleshooting Only by Authorised Personnel
Since the 620 Ohmmeter is used to test potential deadly explosive force detonators and warheads of missiles
etc., personnel that are not qualified to make such electrical repairs on the 620UK Tester should not even
attempt to remove the calibration access screws or open the main panel or effect any repair whatsoever.
Apparent 620 Tester malfunctions can sometimes be the result of bad test lead/connection wiring, wrong
connections, misinterpretation of specifications, low battery levels, and in rare cases due to an incomplete
understanding of the instrument and how to use it. A thorough review of the operating instructions for this
instrument is recommended prior to any component replacement. Check to be sure that cables and other test
equipment are in good working order before attempting to troubleshoot the 620 series igniter tester .
If you turn on the AMPTEC 620UK, display does not come on, it may indicate the batteries need
replacing. If the 620UK exhibits problems that cannot be eliminated by reviewing Chapters B and D, the
following guidelines have been established to help solve the problem.
E-3. CIRCUIT BOARD OPERATION OVERVIEW
There are two main internal printed circuit boards that perform the AMPTEC 620UK “Digital Ohmmeter”
resistance measurement. The AMPTEC 620UK Explosive Safety Ohmmeter uses an independently certified
“intrinsically safe” constant current source (current source PCB). When the intrinsically safe current constant
source is combined with the ohmmeter's digital voltmeter PCB electronics a stable DC resistance measurement
for 0.0001 Ohms to 2.0 Megohms is provided. The digital voltmeter electronics (DVM PCB) uses a high input
impedance sense circuit. The digital voltmeter circuit draws very little current when it measures the DC voltage
drop across the “resistance under test”. The worst case test current (<8mA or less) for each range is indicated on
the AMPTEC 620UK Explosive Safety Ohmmeter/ Igniter Circuit Tester specification page of this manual
(Section B). The AMPTEC 620UK DVM PCB slides in (slot) above the Failsafe Current Source PCB. The
620UK Ohmmeter’s front panel security screws must be removed to access either the DVM PCB (upper slot)
or the Constant Current Source PCB (lower slot).
and the
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The AMPTEC 620UK Ohmmeter Current Source PCB and DVM PCB are epoxy conformal coat encapsulated
both the top and bottom side of each PCB. This PCB encapsulation provides excellent humidity resistance,
moisture condensation resistance, dust and dirt PCB contamination resistance. In additional, it provides PCB
electrical insulation preventing virtually any kind of mechanical circuit damage (loose or broken wire(s), loose
washer, accidental component substitution or component lead damage that can happen while servicing,etc.) and
helps prevent virtually all compromisation of the AMPTEC 620UK Ohmmeter’s EEx-ib IIC-T4 Intrinsically
safe circuitry. In the past, some safety ohmmeters (i.e. ALINCO 101 series) have a history of faulty service
related (i.e. wrong component or electrical current limit fault) failures which have had catastrophic and
deadly result when connected to an explosive device . (Virtually anything can fail when serviced wrong,
i.e. missiles, rocket motors, smart munitions, vital Jet engines etc. )
E-4 AMPTEC 620UK Ohmmeter Assembly/Disassembly Diagram
620UK CASE
Battery wiring
Security Screw
Security
Screw
Security
Screw
BEZEL REAR PANEL
BEZEL
Security
Screw
Security
Screw
Security Screw
Security Screw
(machine thread)
Security Screw
CURRENT
PCB
SLIDE PCB
IN/OUT SLOT
IN SIDE OF
CASE
DVM PCB
Circuit Board Slot
Circuit Board Slot
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OHMMETER
DISPLAY
LCD DISPLAY &
PIC CPU SMART
CONTROL
INTRINSICALLY
SAFE CURRENT
LIMITED SOURCE
PCB
HIGH INPUT
IMPEDANCE
VOLTMETER
PCB
ISOLATED “AA”
BATTERY SUPPLY
A-5 BLOCK DIAGRAM AND CIRCUIT DESCRIPTION
The AMPTEC 620UK Explosive Safety Igniter Tester is a portable digital milli-ohmmeter specifically
designed for ultra-safe resistance testing on bonds in a highly flammable fuel air environment. With 4 1/2-
digit resolution and a low Ohm range of 2.0 Ohms full-scale, the AMPTEC 620UK Ohmmeter provides
ordnance safe resistance measurements and viewing even in direct sunlight.
The AMPTEC 620UK Ohmmeter is constructed in a metal EMI enclosure and internally contains 5 VDCt
HC-MOSS clock operating at 100 KHz for the display, and an HC-MOSS clock operating at 32.7KHz for
the PIC computer chip.
OUTPUT
A-5.1 Principle of Operation
The AMPTEC 620UK Safety Ohmmeter fundamentally uses the familiar principle of "Ohm's Law". It outputs
a constant DC current through a unknown resistance. The DC voltage drop across it is measured and it displays it
(voltage drop) as resistance. The unit’s 2.0 Ohm range outputs an intrinsically safe 5mA level of test current.
When the AMPTEC 620UK outputs 5mA through a 1.0 Ohm resister you should measure a 5mV drop. When you
put that voltage drop into the x10 (times ten) amplifier (only on the 2.0 Ohm range) it becomes 50mV, which
inputs into the DVM PCB and ratiometrically displays the measurement as 1.0000 Ohm. The unit’s 20 Ohm range
outputs the same constant 5mA level (without the x10 amp). When this constant 5.0 mA level is put through a 10.0
ohm resister, you get a 50mV drop, which inputs into the DVM PCB and is displayed as 10.000 Ohms. The 200
Ohm range outputs a constant 500uA DC current. When this current level (500uA ) is routed across a 100 Ohm
resistor you get a 50mV drop, which routes into the DVM PCB and is displayed as 100.00 Ohms. As the 620UK
selected range resistance goes up by a factor of 10 the constant DC current level goes down by a factor of 10
keeping the voltage at 50mV.
4-Wire Kelvin Connections - The V4 version should not use the front panel zero pot (only used with the 2 wire
version) - It is best to keep it (zero pot) turned in the full clockwise position. Connections are made to the front
panel terminals using a 4-wire (Vhigh, Ihigh, Vlow and Ilow) configuration. Proper 4 Wire Kelvin connections
automatically eliminate test lead wire (length) resistance and test lead connection contact resistance offsets (which
is what the zero pot does for 2 wire users). The notched connector end plugs directly into the single access
notched main connector. Turn the connector clockwise until you feel the notch or click of the mating connector of
the 620UK. They have the 4 wire current high, current low as well as the voltage sense high and voltage sense
low routed to the end of the leads. The 4 wires (Kelvin config.) then terminate depending on the style with either a
4 banana jacks or a set of double tipped handheld probes. The 620UK keyed single access connector also
make it extremely difficult if not virtually impossible during normal operation to mis-connect measurement leads
to the 620UK v4 version.
* contact resistance
RESUSTANCE UNDER TEST
LEAD RESISTANCE
*
*
LEAD RESISTANCE
DC CURRENT
LIMITED
CONSTANT
CURRENT
SOURCE
FAIL SAFE
OHMMETER
VOLTAGE
LIMITING
RESISTOR
4.8 VDC BATTERY
T
N
L
E
O
R
O
R
P
U
C
DVM

Localizing the Problem to PCB level
The key to successful troubleshooting is to localize the problem to a general electronic parameter (i.e. current
source or DVM PCB) as much as possible. Certain questions should be asked such as "Does the problem occur
on all ranges or on a specific range only?". If the 620UK Ohmmeter does not come on when powered up, did
you check the power switch.
PCB Exchange/Replacement
If the malfunction is a faulty component, the repair of the AMPTEC 620UK Ohmmeter can be maintained by
replacing the proper internal PCB (Printed Circuit Board) that the faulty component is located on. AMPTEC
620UK Ohmmeter PCBs use ribbon cables with easy to disconnect connectors. There are no serviceable or
faulty component replacements necessary on the 620UK PCBs, it is a case of PCB replacement. AMPTEC
provides a “No-Charge” PCB replacement while the 620UK Ohmmeter is under warranty (1 year) and a small
charge for “non-warranty” repairs.
Use only the specified component or its exact equivalent. Spare replacement PCBs can be ordered from your
nearest AMPTEC RESEARCH Service Center or directly from the factory by referring to the AMPTEC Stock
Number listed in the Parts Lists section at the back of this manual.
A-6 Trouble-shooting or Diagnostic Test Procedure for AMPTEC 620UK Ohmmeter Printed Circuit
Board (diagnosis or replacement)
The following steps will facilitate the proper repair personnel to diagnose whether the AMPTEC 620UK
Ohmmeter Current Source PCB or the Digital Voltmeter PCB needs replacement.
A-6.1 Current Source PCB Diagnostic Routine (bottom internal PCB)
* Place the AMPTEC 620UK Ohmmeter in the 20 Ohm range.
* Put output leads across a 10 Ohm resistance standard (0.005% or better).
* Measure the voltage drop with a DC Voltmeter, it should be 0.05V .
* Place the AMPTEC 620UK Ohmmeter in the 200 Ohm range.
* Measure the voltage drop with a DC Voltmeter, it should be 0.005V.
If any of these tests are not true then the Current Source PCB is faulty and needs replacing.
A-7 PCB replacement Procedure -
Use caution when pulling the PCB from the aluminum case, as there is umbilical wiring and ribbon cabling
that connects the front panel electronics to circuitry mounted inside the 620UK case. Slide boards out to gain
access to the main PCB.
Use the snake eye screwdriver (option “620UK-201) to remove the Ohmmeter’s 4 front panel screws. located
in the corners.
* Pull the front panel forward and carefully slide out the two PCB's.
* Disconnect all wires and cables that go to the bad PCB.
* Reinstall all wires and cables on to the new PCB.
* Follow the calibration procedure (below).
* Slide the two PCB's back in and replace the front panel and screws.
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A-8 620UK Calibration Adjustment Procedure.
All the 620UK Ohmmeter calibration adjustments (trimpots) are located on the DVM PCB (top slot - see
diagram below). The calibration adjustments must take place with the 620UK Ohmmeter Front panel and all
PCBs assemblies must be out of the 620UK chassis.
* Place the 620UK in the 20 Ohm range and short the measurement test leads together.
* Adjust the unit’s front panel “Zero” knob to a full clockwise position.
* Put the measurement test leads across a known 10.0 Ohm resistance standard. (i.e 0.005% or better)
* Adjust RV401 so the display is the value of the 10 ohm resistance standard.
* Next short the measurement test leads together.
* Place the 620UK Ohmmeter in the 2 Ohm range (front panel range select knob).
* Adjust RV403 (see diagram below) for a reading of .0000 on the display.
* Put the output leads across a known 1.0 Ohm resistance standard (0.005%).
* Adjust RV402 so the ohmmeter displays the same value of the 1.0 Ohm resistance standard.
* Reassemble and verify the other ranges (there are no other adjustments needed)
toward the front panel
DVM PCB (top slot)
toward the back (rear panel)
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E-9 Battery Compartment Design and Description
The battery compartment of the 620UK Ohmmeter has been designed in accordance with British Defence
Standard 66-31 and is separate to the main electronics. The battery compartment houses four AA-size
batteries and holder. The supply wires connect the batteries to the Printed Circuit Boards inside the Ohmmeter
passes through a small hole in the side of the battery compartment. This hole is sealed to prevent any fluid
leakage or other failure of the batteries causing damage to the main electronics of the ohmmeter and thus
ensuring that the ohmmeter remains safe at all times. The battery compartment can be secured with standard
screws ( makes it easier for filed install new AA batterries) or can be optionally fitted with security screws.
Tamper-resistant battery compartment lid screws make it extremely difficult for field personnel to install new
batteries. Option “620UK-201” Security Screwdriver (snake-eye type) is available for calibration
maintenance personnel to have access to the unit's battery compartment and internal electronics. The secure
the batteries via a plastic cable tie in the holder to prevent dislodging from the spring contacts of battery
holder.
BATTERY HOLDER LABEL
(4 each Type AA)
Only fit the following battery types:
Duracell Battery Type MN1500, Varta Battery Type 3006,
GP Battery Type GP15G-S4, Ever Ready Silver Seal Type R65,
Every Ready Ultra Plus Type R6F4UP
All batteries fitted must be of the same type.
Authorised service personnel only are to replace batteries.
Batteries must only be replaced in non-hazardous areas.
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