Amptec Research 620LM Manual

RESEARCH
AMPTEC
AMPTEC 620LM Igniter Tester
OPERATION/MAINTENANCE MANUAL
18JUNE2013 REV. B
see website for latest address, contact information and updates http://www.amptec.com
DIODE 2.0 20 2.0K 20M OHMS
5mA 5mA 50uA 50nA
FAILSAFE
CURRENT
25mA
FUNCTION/RANGES
620LMExplosive Safety
Igniter Tester
i 2 3 4 5
.
TEST
i 2 3 4 5
AUSTIN, TEXAS USA - US DEFENSE LOGISTICS CAGE CODE 1CRL2
PHONE [phone]
FAX [phone] website http://www.amptec.com

______________________________________________________
We at AMPTEC RESEARCH would like to thank you, our customer, for selecting our
Failsafe Igniter Tester/ Digital Ohmmeter. Over the past 36 years our experienced
engineering staff have designed, manufactured and supplied earlier versions similar to
the Model 620 and 620 Series Igniter Testers to the U.S. NAVY for the “TOMAHAWK CRUISE
MISSILE”, the U.S. ARMY for the “STANDARD MISSILE”, the U.S.A.F. for the AIM-9 “
SIDEWINDER”, AIM-7 “SPARROW” and AIM-120 “AMRAAM” just to name just a few. We value the
trust our customers have placed with us, and are looking forward to supporting any new requirement you
may have ....
U.S. N.I.ST. CALIBRATION CERTIFICATE
______________________________________________________
AMPTEC RESEARCH, Inc. certifies that this instrument has been completely tested
and inspected and found to meet published specifications as found in this manual on
the date stated on the attached N.I.S.T. Certificate. AMPTEC RESEARCH, Corporation further certifies
that its calibration measurements are traceable to the U.S. National Institute of Standards and Technology.
620 SERIES IGNITER TESTER WARRANTY
________________________________________________________
Permission and a return authorization (RMA) number must be obtained directly from
AMPTEC’s customer service department (via phone, FAX, or email) for repairs
(warranty or otherwise). We need to issue you an RMA number so we can keep track of the instrument and
it’s owner (i.e. who to contact). The warranty period for this instrument is 1 year from when it was first
shipped. AMPTEC RESEARCH will repair or replace the instrument during the warranty period provided
it is returned to AMPTEC RESEARCH, freight prepaid. No other warranty is expressed or implied. We
are not liable for consequential damages. No liability will be accepted if returned without such permission.
Some AMPTEC products may have their design frozen, and no changes will be made without prior notice to
the proper approving authority. Through out this manual, there is reference made using to the generic model
620 series Igniter Testers. There are any versions of the 620 Igniter Tester specifically developed to meet
our customers requirements. The specification, operation, drawing and schematic sections of this manual
contain the unique detail that define the 620LM. Due to continuing product refinement, due to possible parts
going obsolete and other component manufacturer changes, AMPTEC RESEARCH reserves the right on
rare occasions to change any of its products specifications.
R M A
A MESSAGE FROM OUR FOUNDER
Kerry W Clark - Founder, AMPTEC RESEARCH

TABLE OF CONTENTS
_______________________________________________________________
CHAPTER A: RECEIVING AND INITIAL INSPECTION
A-1 Introduction to the AMPTEC 620LM Igniter Tester
A-2 Unpacking and Inspection
A-3 Isolated Continuous Operating Power -
A-4 Setup and Use
CHAPTER B: 620LM FAILSAFE OHMMETER SPECIFICATIONS
Table B-2. Specifications
CHAPTER C: REPLACEMENT, OPTIONAL AND ACCESSORY ITEMS
C-1 Available Accessories and Options
C-2 Test Lead Sets
CHAPTER D: OPERATION, FUNCTION AND USE
D-1 General
D-2 Front Panel
D-3 4-Wire Resistance Measurement
D-4 Connections
D-5 Failsafe Operation
Figure D-1 Error sources in Resistance Measurements

CHAPTER E: GENERAL OPERATION AND DESIGN
E-1 General
E-2 Troubleshooting
E-3 Circuit Descriptions
E-4 Analog-to-Digital Converter
E-5 Ohms-to-DC Converter
E-6 Failsafe Design
E-7 Ultra-Safe Power Supply Scheme
Figure E-1. Model 620LM Block Diagram
Figure E-1B Analog-to-Digital Converter Timing Diagram
Figure E-2 Analog Section of IC1 and IC2
Figure E-3. Constant Current Source Diagram (Simplified)
Figure E-4. LED Display Pin Functions
CHAPTER F: ROUTINE MAINTENANCE
F-1 General
F-2 Required Test Equipment
F-3 Calibration Procedure
F-4 Battery Replacement Instructions
CHAPTER G: COMPONENT PARTS LISTS
620-400 Parts/Assembly list
CHAPTER H: SCHEMATICS AND DIAGRAMS
620LM Main PCB Silkscreen - Reference Designator Map
Drawing 620-070 620LM Main Board Electrical Schematic
(Revision D) (620-070 DVM1 and 640-070 Current (I source) Source
Drawing 620-601-2 620LM Display Board Assembly
Drawing 620-075 620LM Cable Drawing - (Test Leads and Battery Charger)
Drawing 620-077 620LM Relay Board Schematic
CHAPTER I: UPDATES, MODIFICATIONS AND ADDENDUMS

A-1. Introduction to the AMPTEC 620LM
The AMPTEC 630, 640 and now the 620 Series
Igniter Testers/Failsafe Ohmmeters are
becoming the standard in the Safety Igniter
Circuit Test industry, and are designed to
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
Non-Nuclear munitions and the US NAVAL
ORDNANCE CENTER (630BN, 640N and
other versions pending). Some of the devices the
620LM Igniter Tester may be used on include:
fuses, squibs, igniters, explosive bolts, rocket
motor squibs, automobile air-bag initiators and
many others.
The AMPTEC 620LM is a 4-wire failsafe digital
ohmmeter which has been designed to reliably
use very low test currents for its resistance
measurement. Failsafe Output Circuitry
proprietary to AMPTEC RESEARCH ensures
that test current levels do not exceed the
specified "failsafe current" even in a worst-case
component failure situation. The failsafe feature
is tested in every instrument before shipment.
The newer 620 series represent the latest in
ultra-safe Igniter Tester measurements. The
620LM fundamentally uses the same main
printed circuit board (PCB) as all of the
AMPTEC 620A Igniter Testers. The 620LM has
many features which make it useful in a variety
of applications. Please check the last chapter of
this manual for addendums that may apply to the
620LM.
A-2. Receiving, Unpacking, and Initial
Inspection
Should the AMPTEC shipping box appear
damaged upon arrival, request that the carrier's
agent (i.e. UPS) be present when the unit is
unpacked. If the 620LM 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 until the unit is operated or tested to
verify conformance with its specifications.
If the unit fails to operate or fails to meet the
performance specifications of Section B, notify
the carrier's agent and the nearest AMPTEC
Sales Office. 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 RESEARCH first, prior
to just returning the 620LM , 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).
We may possibly be able to fix the problem over
the phone and prevent you from having to return
the unit to AMPTEC for repair.
R M A
SECTION A - RECEIVING AND INITIAL INSPECTION

A-3. Isolated Continuous Operating Power -
Isolated continous operating power for the
AMPTEC 620LM Igniter Tester is derived via a
multiple levels of isolation electronics and circuits
for safety reasons (not D cell battery power). There
is a AC/DC Wall Adaptor with a special polarized
Molex connector that provides the first level of
isolated 24 VDC input (rear panel) into the meter.
This AC/DC Wall adapter accepts 115 VAC input
(60Hz) and provides basic wideband AC Noise
Isolation and a conditioned 24 VDC input for the
meter.
Inside the meter is DC/DC Isolation circuitry with 3
KV of isolation from the input DC voltage. This
internal circuitry provides a conditioned 6 VDC to
operate the meter’s measurement circuitry.
The isolated AC/DC Wall adapter is fitted with a
polarity keyed box type Molex connector plug #
436040-0200. This helps prevent the accidental use
of any non approved AC/DC Wall Adapter from
being plugged into the AMPTEC 620LM rear panel
power port (Molex 436040-0200 mate connector)
There is NO “Power” switch to operate the
620LM Igniter Tester. The meter is hardwired
to be “ON” whenever power is applied to the
safety meter’s mating Molex connector on the
rear panel.
A-4. Setup and Use
The AMPTEC 620LM Igniter Tester may be
setup to operate within minute(s) of power "turn
on" (unless your in an extremely cold
temperature - allow more time for warm-up - 15
minutes).
The AMPTEC 620LM consumes little power
and generates virtually no heat. Consequently,
it may be used in any area where the
environment does not exceed the specifications
of Table B-2.
Avoid exposing the AMPTEC 620LM to
extremes of temperature which will affect
accuracy and stability of the product.
Fuse
(2 Amp-fast blo)
Molex connector plug # 436040-0200

CHAPTER B - 620LM EXPLOSIVE SAFETY
IGNITER TESTER - SPECIFICATIONS
______________________________________________________________
Diode Test (Voltage Forward) Test Current levels - 0.5mA/<25mA Failsafe
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)
2.0W range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ±0.02% of reading ±0.05% of range
20W and 2 KW ranges . . . . . . . . . . . . . . . . ±0.02% of reading ±0.02% of range
20 MW range . . . . . . . . . . . . . . . . . . . . . . . . . . . ±2.0% of reading ±0.2% of range
Temperature Range
Operating 0°C to 50°C
Storage -10°C to 70°C
Temperature Coefficient
20W and 2 KW ranges ±0.002% per °C (from 0°C-15EC and 35°C-50°C)
Instrument Display . . (20,000 count) 4½ digit Super Bright Light Emitting Diodes (LED)
Over-Range Indication . . . . . . . . . . . . . . . . ( select next higher range) Display flashes
Measurement Update Rate . . . . . Approximately 300ms
Voltage Protection - Maximum Input . . . . 250VDC or AC without damage
peak
Open Circuit Current Source Compliance Voltage . . . . . clamped at ~1.6 volts
Power . . . . . a modified mating connector version of OP 247 a dual stage Isolated (3 KV Isolation)
Continuos Operating power. See OP 247 schematics for further details. The dedicated mating connector
from the AC/DC adapter for the rear panel input is used to prevent the wrong power adapter being used with
this product.
Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.5" (24cm) W x 11" (27cm) D x 3"(8cm) H
Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 lbs net; 7 lbs shipping
620LM Resistance Range/Resolution 620LM Nominal Test Current/Failsafe Current Levels
2.0 W 20 2.0 K 20 MW W W
100 µW 1.0 m 100 m 1 KW W W 2.0 W 20 2.0 K 20 MW W W
5mA 5 mA 50µA 0.01 µA
8mA 8mA 150 A 0.015µAµ
2.0 (I.9999) Ohms Fullscale with
0.1 milliohm (100 µ ) Resolution
620ES Explosive Safety Igniter Tester

C-1. Available Accessories and Options
Listed below are the options available for use with
the AMPTEC 620A Series FailSafe Ohmmeters.
Option 620LM-DC: AC Power Adapter Line
Conditioner
Option "620LM-DC" is an AC/DC Wall adapter that
safely converts and conditions 115VAC line voltage
to 24VDC at 300mA. One adapter is provided as a
standard accessory with every 620LM . It is fitted
with the mating Molex connector that is specifically
compatible with the meters rear panel molex
connector. Additional Isolation electronics is insode
the AMPTEC 620LM but this particular AC power
adapter has been shown to continuously provide
isolated DC power (to 3 KV AC and 3 KV DC) for
the AMPTEC 620LM Igniter Tester.
Option 100: Carrying Case
Option "100" is a hardshell (impact resistant plastic)
shock absorbing foam lined meter and accessory
carrying case for the 620A Ohmmeter with extra
room for test leads, battery charger, Kelvin Clip Test
Leads, Connector Adapters, single pointed probes
and operator manual etc.
Option RACK: Rack Mount Adapter
Option "620RACK" includes an adapter tray that
allows any AMPTEC 620 series tester to be flush
panel mount installed in a standard 19" NEMA
equipment rack.
Option “500” Optically Isolated Analog
Output
New Options and Custom Leads Available
Contact the sales department at AMPTEC
RESEARCH (phone [phone]) if you
have need for a special probe, adapter, lead set,
or custom option not listed in this manual.
AMPTEC’S experienced application engineers
have helped supply many customers with special
igniter tester accessory requirements.
This rear panel mounted isolated analog DC
Voltage output signal is directly proportional to
the 620 tester's ohm display measurement. (i.e.
1.2345 VDC for 12.345 ohms). It is used to track
620 tester measurements for datalogging pur-
poses with an external device (i.e chart recorder,
system DMM with GPIB). Isolation protection is
rated @2000 volts peak to insure any instrument
connected to "Option 500" has virtually no
impact on the 620 series tester's safety.
SECTION C OPTIONAL ITEMS AND
ACCESSORIES

Calibration Access Screws
Recessed in the four feet on the bottom of the
AMPTEC 620LM you will note there are 4
screws (phillips head type) that are used for
calibration access. These screws are meant to
remain intact and should only be removed by
authorized personnel (i.e. Calibration Lab staff).
Optional Functional Test Box with built-in
milliammeter
An optional Functional Test Box (option FTB-
620ES) for the AMPTEC 620LM contains an
analog 10 mA full-scale milliammeter and a
variety of test resistors is available from
AMPTEC RESEARCH.
D-1. General Operation
This section contains operating instructions for the
AMPTEC 620LM Explosive Safety Igniter Tester.
D-2. Front Panel Features and Operation
NO Main Power Switch
The AMPTEC 620LM Igniter Tester was designed
for automated RS232C use (range changes and
measurements via isolated serial computer
interface). The AMPTEC 620LM Igniter Tester is
always hardwired ‘ON”, there is no power ON /
OFF switch. When proper power is applied to the
oolarized rear panel molex connector, the meter is
‘ON”, when rear panel power input is removed it
is “OFF”. Although this “power” is also further
isolated and conditioned inside the meter, this
(special molex jack rear panel input) is the only
source of power for the AMPTEC 620LM.
NO Range Switches
The AMPTEC 620LM has NO range switches as
it was not designed to be manually operated.
There are No pushbuttons or even test lead jacks
on the front panel.
Over-Range Indication
If the resistance being measured (including "Open
Circuit/ Disconnected states") is a higher value
than the selected range, the instrument's display
will flash (blink) , which indicates "overrange" .
Gold Plated Rear Terminal Inputs
The AMPTEC 620LM has no front panel
connections. All reistance measurement inputs are
via the rear panel terminal strip. The AMPTEC
620 user can directly connect a bare wire to the
appropriate termanl screw (Voltage High and
Voltage low , and Current high and Current low
labeled as Vhigh,Vlow, Ihigh,Ilow .
CHAPTER D - OPERATION, FUNCTIONAL
AND USE

AMPTEC 620LM Rear Panel with RS232C I/O
Item 1 - The AMPTEC 620LM rear panel (shown above)
contains many jacks, terminals, labels, and stickers.
The special AC to DC Adapter (item #1) must be left in
the rear panel jack in order to operate the meter, as it is
fitted with option "247" (Isolated Continuous Operating
Power).
.
Item 2 is the fuse holder - replace with a 2 ampere 3 AG
type fast blow fuse (rarely needs replacing).
Item # 3 - RS232C Serial Interface is a safety isolated
RS232C serial I/O with 9 pin D type Sub-min connector.
This RS232C Interface provides the meter’s resistance
measurements to a PLC fitted with a serial port. The
RS232C protocal settings should be 9600 Baud, 8 Bits,
No parity , 1 Stop Bit , 9 pin D Sub-min connection.
RS232C Command Set
Note commands are case sensitive.
C Continuous Read Mode - RS232C I/O outputs
a data string every A to D conversion cycle, approx. 2.5
times per second.
S Single Read Mode - RS232C I/O outputs a
single data string upon reception of a “R” command.
R Read - Commands RS232C I/O to output a
single data string ( 1 resistance reading).
ASelects Auto-Range mode
r0De-Selects all Ranges
r1 Selects the 2.0 Ohm Range
r2 Selects the 20 Ohm Range
r3 Selects the Diode Test function
r4 Selects the 2K Ohm Range
r5 Selects the 20K Ohm Range
r6 Selects the 200K Ohm Range
r7 Selects the 20M Ohm Range
VVersion commands board to output the firmware
version string.
*
The isolated AC/DC Wall adapter is fitted with a
box style polarity keyed Molex connector plug # 436040-
0200. This helps prevent the accidental use of any non
approved AC/DC Wall Power Adapter from being
plugged into the AMPTEC 620LM rear panel power port
(Molex 436040-0200 mate connector)
Data Format - The RS232C I/O outputs a data
string with the following format:
1.2345E+3 The measurement is usually in Ohms
+3
(where E+3 = 10 scientific notation style) . The
Exponent is defined below. 1.2345E+3 = 1.2345
+3
+3
KOhms (where E =10 ). 1.3700E+1 = 13.700
+1
+1
Ohms (where E =10 )
Range Exponent
2.0 Ohm E+0
20.0 Ohm E+1
Diode Test E+0
2.0 K Ohm E+3
20 K Ohm E+4
200 K Ohm E+5
20 MOhm E+7
Overrange is indicated by 9.9999Enn .Where nn is
the selected resistance range exponent. A Range
Error is indicated by x.xxxxERR.
Item # 4 is the unit’s serial number sticker.
Item # 5 is the gold plated 4 terminal rear terminal
strip (they are wired in parallel with the front termi-
nals). If a “2 wire ohms” connection is made then
the V high and I high terminals should be shorted
together, and the V low and I low terminals should
be shorted. The 620LM Voltage High, Voltage
low, Current High and Current Low wires are
permanently connected to the gold plated rear
terminal strip (see labeled gold plated terminal strip
on rear panel).
Item #6 Calibration Sticker - If the calibration
due date has expired ( 1 year) AMPTEC or a Cal.
Lab can contacted to re-certify the AMPTEC
620LM Explosive Safety Ohmmeter/Igniter Tester.
contact AMPTEC customer service see website
www.amptec.com
LM
LM
LM
LM
LM

D-3. 4-Wire Resistance Measurement
The four-terminal configuration of the 620LM
eliminates measurement errors normally caused
by "in series" test lead resistance and "contact"
resistance.
In many resistance measurement applications the
contact resistance and can exceed the value of
the test resistance by several orders of magni-
tude. The AMPTEC 620LM overcomes this
potential error source by providing two terminals
of constant current (I high and I low) and an
additional two terminals for high impedance
voltage measurement. The constant current
source uses a variable compliance voltage circuit
to overcome lead and contact resistance until the
current loop is a constant level. The result is a
fast, accurate resistance measurement of the test
resistance, independent of the resistance of the
current carrying leads.
Figure D-1 above illustrates the 4-wire principle
eliminates lead, wire and contact resistances as
potential error sources. The internal constant
current source inherently overcomes all series
resistance (within compliance voltage limits) and
delivers a precise constant current. Separate DC
to DC isolation circuitry provides independent
circuit voltage supplies for both polarities of
the constant current source circuit. The internal
high-impedance Digital Voltmeter (DVM)
senses the voltage drop across the test resistance
(i.e. squib or detonator). There is negligible
contact and lead resistance error created by the
voltage measurement because the high input
impedance of the DVM limits current flow in the
voltage (Vhi and Vlow) leads.
D-4. Connections
Connections are made to the front panel termi-
nals using a 4-wire configuration as described in
section D-3.
Next connect the 4 wire Kelvin wires or test
leads into the AMPTEC 620LM Igniter Tester
rear panel.
For 620 series test leads other than those termi-
nated with banana plugs, RG-58 Shielded Coax
Cabling is recommended. Customer built test
wiring should maintaining the four wire Kelvin
measurement if possible. Make the current con-
ductor the largest conductor and keep the voltage
sense input shielded or inside the current shield.
The AMPTEC 620 series Igniter Tester's five
way input jacks allow for customized wire con-
nections, extended kelvin wiring (beyond 100
feet depending upon conductor gauge), cables
terminated with spade lugs, and special banana
jacks can all be used with most AMPTEC 620
series Igniter Testers.
All AMPTEC ohmmeters use a high impedance
voltmeter as part of the resistance measurement
process. This voltmeter is a highly accurate and
stable 4½ digit analog-to-digital converter (A to
D). The high impedance DVM must receive a
voltage drop in order to display the proper value.
When the DVM is not receiving a definite input
signal, the output reading from the Analog to
Digital Convertor can appear random and wan-
dering. The display may indicate a randomly
wandering number or it may indicate an
overrange (flashing) condition. This unpredict-
able display (No input to the DVM) condition is
not a malfunction, in fact, just a characteristic of
the high impedance voltmeter circuit and should
not be mistaken for a fault in the instrument -
- - - - - continued next page - - - -
IGNITER TESTER
Figure D1 - Igniter Tester Kelvin Block Diagram
* contact resistance
*
*
IGNITER
LEAD RESISTANCE
LEAD RESISTANCE
P
O
O
L
T
N
E
R
R
U
C
DC to DC ISOLATOR
HIGH IMPEDANCE VOLTMETER
4.8 VDC BATTERY
DC to DC ISOLATOR
COMPLIANC
VOLTAGE
LIMITED
CONSTANT
CURRENT
SOURCE
E

As this condition is simply a state of an “open
circuit” or “nothing connected” to the DVM
circuitry. A flashing display (on and off usually
all zeros) indicates an over-range condition when-
ever the test lead terminals are open, or the resis-
tance under test is a higher value than the range
selected on the AMPTEC 620 tester. Connecting
VHI to IHI and Vlo to Ilo eliminates the wander-
ing (open circuit) display condition.
By using a 4-wire Kelvin type lead set or by
shorting the V and I terminals together and
HI HI
V and I terminals together the instrument
low low
is in the 2 wire resistance mode.
Resistance Offset in 2 Wire mode
All wiring including harness wires from the two
wire test connection out, are "in series" with the
test squib resistance and become part of the actual
two wire measurement (another potential source
of measurement error if not compensated for) .
Many Ordnance test procedures have the 620
series Igniter Tester user short their wiring
harnesses at the very end (by the squib) and
record the resistance value or offset. Then when
the 620 series Igniter Tester leads, including the
in-series harness wiring resistance, is connected
to the test squib, the squib test resistance can be
calculated (via subtraction of the 2 wire harness -
test lead resistance offset).
That is the 2 wire lead length shorted offset
resistance (without the squib resistance) can be
subtracted for the total resistance (including the
squib resistance) to determine the actual squib
(test) resistance.
Identifying a Test Connection problem
A precision 1.0 Ohm test resistor test resistor can
be used for testing mid-scale performance of the
2.0 Ohm range. Performing a similar Functional
Test with the 620LM meter across the 1.0 Ohm
test resistor should get a reading close to 1.00
Ohm (i.e. 0.9995 Ohms is OK). If the 620 Series
Igniter Tester appears OK after checking eaqch
range against a known resistance then the
connection problem must be outside of the 620
series meter (i.e your wiring harness or the actual
device under test connection.) If the 620 series
meter doesn’t agree with the test resistors, then
the meter or it’s test leads are most likely broken.
If this case, please contact your local AMPTEC
RESEARCH Service Office, or call 1-800-350-
5105 or [phone] (International
Overseas) or FAX[phone], email
[email protected]
The AMPTEC 620 display should indicate a
stable reading when the test leads are securely
attached to the device under test. If the display
appears to be erroneous when connected to the
resistance under test, recheck the test leads for
integrity and cleanliness. If all external items
appear to be functioning properly, the next step
in problem isolation and diagnosis envolves
general trouble-shooting principles. If a
measurement problem appears on the 2.0 Ohm
range of the meter, test for a zero offset problem
first. Plug the 620 with Kelvin test leads into a
0.10 test resistor (i.e. AMPTEC # FTB-620ES).
If the meter doesn’t display a value close to 0.1
Ohms adjust the zero (see calibration procedure
chapter). The zero adjustment trimpot only has
enough span to zero out the 620 series test
leads. The meter’s zero adjustment pot wasn’t
designed to zero out a 100 feet of 2 wire
harness.
D-5. Failsafe Operation
The AMPTEC 620LM Igniter Tester uses a fail-
safe constant current source design that renders
them incapable of delivering excessive voltage
or current to the device under test. The typical
fail-safe current for each range is indicated with
most AMPTEC models under the corresponding
range switch on the 620 series meter front
panel. Please refer to section E-6 for a technical
description of the failsafe circuitry specifics.
As a further precaution the 620LM Igniter
Tester is line isolated from the AC line to 3 KV
DC or AC when only used 620LM-DC AC wall
Power Adapter/conditioner (supplied with the
meter).
As this meter is fitted with the Diode Test
function the nature of this circuit uses higher
compliance voltage. As a result the failsafe
current limit is 25 mA.

CHAPTER E GENERAL OPERATION AND DESIGN
E-1. General
The AMPTEC RESEARCH 620LM Explosive
Safety Igniter Tester is shown in the block dia-
gram (Figure E-1). All diagrams and informa-
tion disclosed in this chapter is proprietary and
is included in order to make troubleshooting to
component level possible.
The AMPTEC 620 Series Igniter Tester uses
modern solid-state semiconductors exclusively
and digital CMOS circuits extensively to mini-
mize power requirements and make battery
operation useful and practical. AMPTEC also
maintains a spare parts inventory of all compo-
nents found in the 620LM Tester and it’s cus-
tomer service department can also provide
additional assistance in the trouble shooting
process.
E-2. Troubleshooting
Since the 620LM Tester 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 620LM
Tester should not even attempt to remove the
calibration access screws or open the main
panel or effect any repair whatsoever.
Apparent 620LM Tester malfunctions can some-
times 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 620LM
series igniter tester .
If you turn on the AMPTEC 620LM Explosive
Safety Igniter Tester and the display does not
come on, it usually means the batteries are
dead and need charging, or fuse needs replac-
ing.
If the 620LM exhibits problems that cannot be
eliminated by reviewing Chapters B and D, the
following guidelines have been established to
help solve the problem.
E-2-1. Localizing the Problem
Chapter D-2 discusses how to use the
Functional Test Box (FTB-620ES) with the
620LM Tester to help localize the problem. The
key to successful troubleshooting is to localize
the problem to a general electronic parameter as
much as possible before trying to pin the
problem down to a specific component. Certain
questions should be asked such as "Does the
problem occur on all ranges or on a specific
range only?". If the 620LM Tester does not
come on when powered up, did you check the
rear panel fuse. The power supplies for both the
current source and the digital voltmeter
electronics are also one of the first things that
should be tested. As it is not possible to
anticipate all failure modes of the 620LM
Explosive Safety Igniter Tester, servicing
personnel should become familiar with this
section to gain a complete understanding of the
internal workings of the ohmmeter.
E-2-2. Component Replacement
If the malfunction is a faulty component, the
accuracy of the 620 Series Igniter Tester can be
maintained only if it is re-calibrated after a
component replacement and the following
precautions are taken:
Use only the specified component or its exact
equivalent. Spare parts 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.
The highest quality 63/37 grade rosin core
electronic grade solder with a 50W or lower
maximum power soldering iron should be used.
Never use an acid core solder as corrosion of
components leads and PCB etch loss can occur.

When soldering, heat the PCB pad and the lead
of the component, not the solder. After several
seconds of the component lead in contact with
the hot soldering iron apply solder smoothly and
evenly onto the PCB pad and component lead
not the soldering iron. Do not touch or move
the replacement part until the solder has cooled.
Cold solder and bad solder joints can cause
more problems.
Use the chassis ground (connect to the common
terminal of the functional test section)
connection - i.e. connect to an earth ground to
avoid a static discharge to a static sensitive
component. Handle all 620LM internal
components as if they are static sensitive if you
are not sure.
See Next Page for Start of 620 Circuit Descriptions and Functional Diagrams

E-3. Circuit Descriptions
The circuit descriptions which follow are
referenced to Figures E-1, E-2, E-3 and the
schematic diagrams at the back of this manual.
In the following descriptions, references to
integrated circuits are given in the form "IC201-
1", which refers to Integrated Circuit 201, pin 1.
E-4. Analog to Digital Conversion
The A to D conversion is done with a ICL8068
/ICL71C03 chip set. The ICL8068 takes care of
the analog part and the ICL71C03 takes care of
the digital part of the 4 ½ digit 20,000 count
dual slope conversion.
COUNTERS
DISPLAY
COMPARATOR
BUFFER
MULTIPLEXER
ZERO
CROSSING
DETECTOR
INTEG
UUT
CONTROL
LOGIC
INPUT
SWITCH
DC CONSTANT
CURRENT SOURCE
RANGE
SWITCH
Figure E1 - AMPTEC 620LM FUNCTIONAL BLOCK DIAGRAM
COUNTS
PHASE I
I0.00I I0.000 20.00I
4 ½ DIGIT
PHASE II PHASE III
NUMBER OF COUNTS TO ZERO CROSSING
PROPORTIONAL TO VIN
AFTER ZERO CROSSING,
ANALOG SECTION WILL BE
IN AUTOZERO CONFIGURATION
BUSY
OUTPUT
INTEGRATOR
OUTPUT
CLOCK
AZ PHASE l INT PHASE ll DEINT PHASE ll AZ
INTERNAL
LATCH
POLARITY
DETECTED
ZERO CROSSING
OCCURS
ZERO CROSSING
DETECTED
Figure E1B - 620 Conversion Timing Diagram

ZERO CROSSING
DETECTOR
BUFFERBUFFER
1 µF
INTEGRATOR
COMPARATOR
CAZ
CSTRAY
RINT
FIGURE E-2A. PHASE l AUTO-ZERO
CINT
VIN
CREF
3
1
2
6
5
4A2
A1
A3
_
+
_
+
_
+
ZERO CROSSING
DETECTOR
ZERO CROSSING
DETECTOR
POLARITY
FF
POLARITY
FF
BUFFER
BUFFER
BUFFER
BUFFER
1 µF
1 µF
INTEGRATOR
INTEGRATOR
COMPARATOR
COMPARATOR
CAZ
CAZ
CSTRAY
CSTRAY
RINT
RINT
FIGURE E-2B. PHASE ll INTEGRATE INPUT
FIGURE E-2C. PHASE lll AND DE-INTEGRATE
CINT
CINT
VIN
VIN
CREF
CREF
3
3
1
1
2
2
6
6
5
5
4
4
A2
A2
A1
A1
A3
A3
_
+
_
+
_
+
_
+
_
+
_
+
ZERO CROSSING
DETECTOR
POLARITY
FF
BUFFERBUFFER
1 µF
INTEGRATOR
COMPARATOR
CAZ
CSTRAY
RINT
FIGURE E-2D. PHASE lll AND DE-INTEGRATE
CINT
VIN
CREF
3
1
2
6
5
4A2
A1
A3
_
+
_
+
_
+
Figures E2. Main Analog Section of DVM Circuit - IC1 and IC2

Detailed Description
Analog Section
Figures E2 diagrams A thru D shows the
equivalent circuit of the analog section in 3
different phases of operation. The system will
perform conversions at a rate determined by the
clock frequency 40,002 clock periods per cycle.
(see Figure E1B shown earlier in this chapter for
details of conversion timing).
Auto-Zero Phase I (Figure E2A)
During the Auto-Zero, the input of the buffer is
connected to V REF through switch 2, and
switch 3 closes a loop around the integrator and
comparator, the purpose of which is to charge
the Auto-Zero capacitor until the integrator
output dose not change with time. Also,
switches 1 and 2 recharge the reference
capacitor to V REF.
Input Integrate Phase II (Figure E2B)
During Input Integrate the Auto-Zero loop is
opened and the Analog Input is connected to the
Buffer Input through switch 4 and C REF if the
input signal is zero, the buffer, integrator and
comparator will see the same voltage that
existed in the previous state (Auto-Zero). Thus,
the integrator output will not change but will
remain stationary during the entire input
integrate cycle. If V IN is not equal to zero, and
an umbalanced condition exists compared to the
Auto-Zero Phase, the integrator will generate a
ramp whose slope is proportional to V IN.
Deintegrate Phase II (Figures E2C and
Figures E2D)
During the Deintegrate phase, switch 5 is closed
and a voltage which is V REF more positive
than during Auto-Zero is impressed on the
BUFFER INPUT. Thus the referance capacitor
stores the equivalent voltage. This returns the
output of the integrator to the zero crossing
point established in Phase I. The time, or
number of counts, required to do this is
proportional to the input voltage.
E-4-1. Reference Voltage
The precision reference voltage required to do
the A/D conversion is developed by IC201. The
zener voltage is attenuated to approximately -
0.5V . This voltage is applied to IC2-7 .
E-4-2. LED Display
The output format from IC2 is in Binary Coded
Decimal (BCD) format. Each digit is scanned
for 10 clock pulses. The scan sequence is D5 D4
D3 D2 D1. This drives Q1 thru Q5, which in
turn drivers the seven segment displays. The
BCD data is converted to seven segment format
by IC4. When the 620LM electronics are in
open circuit or over-range mode the display
flashes “0000". IC5 is a 1 MHz oscillator
which is divided by 10 by IC6. The 100 KHz
clock output then goes to IC2.
E-5. Ohms-To-DC Converter
The ohms-to-DC converter generates a constant
current which is passed through the device under
test to develop the voltage measured by the A/D
converter.
E-5-1. Constant Current Source
The constant current source is composed of
IC201, IC202, Q202, D203 and their associated
components. The input to the constant current
source is approximately +1.05 volts, developed
at IC201-7 and connected to IC201-13 through
R209 and R210. The heart of the constant
current source is the voltage-to-current
converter. A simplified schematic of this circuit
is shown in Figure E-4 and described in Section
E-5-2. The amplifier of IC201-12 is an invertor,
and its output is applied to IC201-9. The
amplifier of IC201-8 has unity gain due to the
feedback through R213 . Its output is applied
to the inverting input of IC202-3. The output of
IC202-6 provides feedback to the non-inverting
input of IC201-10. This circuit operates to
maintain the inverting input at IC202-3 and the
non-inverting input at IC202-2 at the same
potential.

E-5-2 Constant Current Circuit Operation
Assume that terminals I and I of Figure E-3
hi lo
are shorted, and 1.0 volt is applied to E so that
in
I is positive. To equalize the 1.0 volt applied to
hi
Ein , the inputs of IC202, IC201 must be driven
to zero. This condition occurs only when the
voltage drops across R212 and R222 are equal
to the drops across R213 and R221. For these
voltage drops to be equal, the output of IC202
must be at +1.0 volt. Since the output of IC201-
8 must be zero, the drop across R213 is 0.5
volts, making the inverting input 0.5 volts. The
drops across R212, R221 and R222 will also be
0.5 volts. Since the inputs to IC201 are
essentially equal, its output is zero (offset by the
few microvolts required to drive IC202 to +1.0
volt). Under these conditions the sum of the
voltages across R212, R213 , R221 and R222
equals the sum of E plus the output of IC202.
in
Consider now that the short is removed from the
I and I terminals and a 100-ohm resistor (R )
hi lo L
is connected in its place. The current through R
L
increases the voltage at the input to IC201. A
balanced condition will be reached when the
output of IC201 is equal to the non-inverting
input of IC202. Again, this condition occurs
when the voltage drops across R212 and R222
are equal to the voltage drops across R213 and
R221. At this time the output of IC202 is 1.0
volts. The voltage drop across the range resistor
is 1.0 volt, just as it was when the output
terminals were shorted. The current through R
L
is 5 milliamperes, just as it was through the
jumper when the output terminals were shorted.
E-6. Failsafe Design
Reference to the AMPTEC 620ESTester Igniter
Tester schematic will show that the output of
IC202-6 is actually applied to the base of
transistor Q202, which acts as a current limiter.
The worst-case component failure that could
occur in this circuit would be a Q202 short,
which would effectively connect the -5 volt
supply directly across R218, D202, the range
resistor and R .
L
D203, however, acts as a 1.6 volt zener diode,
limiting the voltage that can appear across these
components. Even if every component in the
amplifier circuit shorted, the current through the
igniter could not exceed safe limits, because the
-5 volt and +5V supplies includes inherent
current limiting. Because of the design of both
supply isolation transformers T101 and T102,
the ±5 volt supplies can only deliver 20 to 25
milliamperes before the DC/DC converter
disengages, dropping the -5 volt output to zero.
See Section D.
620LM Failsafe Current Calculation - Worst
case Component Failure
Voltage limiting diode, D203, provides a 1.6
volts maximum across R227 (10W) and R223
(100W), which are 110 Ohms across the Igniter
Testers output terminals.
(Imax) Current Maximum Calculation
1.6V/110 ohms = 0.014 Amperes
(15mA) max
The AMPTEC 620LM Tester is powered by a
rechargeable internal battery pack and cannot be
operated directly from the battery charging
adapter. This is to eliminate the possibility of
an electrical short to/from the AC line. Only
when the 620 POWER switch is in the “OFF/
CHARGING” position are the batteries
connected to rear panel charging jack. When
the POWER switch is in the ON position, the
batteries are disconnected from the battery
charger and connected to the internal circuits of
the AMPTEC 620 Igniter Tester.
x
R212
100K
R213
100K
R222
100K R221
100K R215
100K
RANGE
ATTENUATION
RESISTOR
RL
I hi
I Lo
E in
Figure E-3 Constant Current Circuit
IC201 IC202
This applies to all Resistance ranges/mode except for Diode Teste Mode

The 620LM Tester measurement circuitry is also
failsafe current limited, even under worst case
component failure.
E-7 . Ultra-Safe Power Supply Scheme
The +5 volt power supply is provided directly
by the batteries (for driving the LED displays
and digital logic). The ±5VD is used for driving
IC8, the low battery detection circuit. The ±15V
power supply is generated by IC7 for the digital
voltmeter (DVM) chip set (IC1 and IC2).
The ±5 VA is developed by one DC to DC
convertor circuitry: composed of Q103,Q104,
T102, D103, D104, IC102 for the negative
polarity. The other DC/DC convertor is
composed is composed of Q101, Q102, T101,
D101, D102 and IC101 for the positive polarity.
8
A
B
G
F
CE
D
D.P.
SEGMENT PIN
A . . . . . . . . 1
B . . . . . . . . 13
C . . . . . . . . 10
D . . . . . . . . 8
E . . . . . . . . 7
F . . . . . . . . 2
G . . . . . . . . 11
D.P. . . . . . . . . 6
Common . . . . 14 8
PIN
1
2
3
4
5
6
7
PIN
14
13
12
11
10
9
8
Figure E4 - 620 series LED Display Pin Out Detail/Functions

F-1. General
This section of the manual contains routine
maintenance information regarding the
AMPTEC RESEARCH 620LM Igniter tester.
Calibration should be performed on a regular
basis to ensure continued instrument accuracy
or following a main PCB electronic component
repair/replacement. The recommended
calibration interval is 1 year.
The AMPTEC 620LM igniter tester is a four
wire Kelvin ohmmeter. The AMPTEC
Igniter Tester must be calibrated using four
wire Kelvin connections to the resistance
standard in order to eliminate lead resistance
and contact resistance errors. The rear panel
terminal strip (Vhigh, Ihigh, Vlow, Ilow) 4-wire
configuration must be maintained up to the
point of the connection to the resistance
standard (for any range below 200Kohm).
F-2. Required Test Equipment
Following standard resistors are required to
calibrate the 620LM Igniter Tester .
Precision Resistors:
0.01 ohm ± 0.01% Accuracy or better
1.0 ohms ± 0.005% Accuracy or better
10 ohms ± 0.005% Accuracy or better
1.0 Kohm ± 0.005% Accuracy or better
10 MegOhm ± 0.10% Accuracy or better
14 Kohm ± 0.10% Accuracy or better
Test Leads:
Rear panel connected 4-wire Kelvin Test
Lead wiring (Vhigh, Ihigh, Vlow, Ilow) is
needed to eliminate in-series resistance errors or
offsets (for calibration and accuracy purposes).
F-3. Calibration Procedure
The AMPTEC 620LM should be calibrated but
first it should be allowed to warm-up for a
minimum of 15 minutes before beginning the
calibration procedure.
620LM
The calibration trimpot adjustments are
accessed by removing the screws in the feet of
the unit, then lifting off the lid. This provides
access to the main PCB trimpots. The locations
of the adjustments are shown on drawing
number 620-600 at the back of this manual. The
meter’s ranges are selected via (computer
command) the optically isolated RS232C serial
interface.
F-3-1. Zero Offset Adjustment (20 ohm and
higher ranges)
1. Connect the rear panel 4 Wire Kelvin
measurement leads to the 10 ohm standard
resistor. Using the RS232C interface
(commands) select the 2 KOhm range.
2. Adjust potentiometer RV2 for a display
indication of 0.0100 KOhms . Do not over
adjust RV2 past a 0.0100 reading.
F-3-2. Full Scale Adjustment (20 ohm and
higher ranges)
1. Still on the 2.0 Kohm range. Connect the
Kelvin leads to the 1.0 Kohm standard resistor.
2. Adjust RV1 for a display reading of 1.0000
Kohm.
F-3-3 2.0 ohm range Zero adjustment
1. Using the RS232C interface (commands)
select the 2 ohm range. Connect the 4 wire
Kelvin leads to the 0.01 ohm standard resistor.
2. Adjust potentiometer RV5 for a display
indication of 0.0100 Ohms .
F-3-4. 2 ohm range Full Scale Adjustment
1. Select the 2 ohm range. Connect the rear
panel
test leads or wiring to the 1.00 ohm standard
resistor.
2. Adjust RV6 for a display reading of 1.0000
Ohm.