Amptec research 620a-4 Manual

T.O 33D5-14-52-1

OPERATION / MAINTENANCE MANUAL

AMPTEC RESEARCH MODEL 620A-4

FAILSAFE DIGITAL OHMMETER/

IGNITER CIRCUIT TESTER

NSN 6625-01-460-1499AQ

DISCLOSURE NOTICE: This Information Is furnished upon the condition that It will not be released to

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whether patented or not, will be respected, that the recipient will report promptly to the United States, any

known or suspected compromise, and that the Information will be provided substantially the same degree

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markings on the document, It will not be downgraded or declassified without written approval of the

originating United States agency.

DISTRIBUTION STATEMENT: Distribution authorized to U.S. Government agencies only, administrative or

operational use, 18 August 1992.. Other requests for this document shall be referred to O0-AI.C/TIED, Hill

AFB, Utah 84056-5820.

WARNING: This document contains technical data whose export Is registered by the Arms Export Control

Act (Title 22, U.S.C., Sec 2751 et seq) of the Export Administration Act of 1979, as amended (Title SO, U.S.C.,

App 24O1 et seq). Violations of these export laws are subject to severe criminal penalties. Disseminate In

accordance with provisions of AFI 61-204.

HANDLING AND DESTRUCTION NOTICE: Comply with the distribution statement and destroy by any

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Published under authority of the Secretary of the Air Force

18 JULY 2000

ORIGINAL

AMPTEC RESEARCH IS AN ISO 9001:2015 CERTIFIED QUALITY MANAGEMENT COMPANY

OPERATION/MAINTENANCE MANUAL

REV. G

AMPTEC 620A-4 Fail Safe

Digital Ohmmeter /Igniter Tester

LOW

BATTERY

Mil Std 810- Method 511 rev F certified compliant for

use in " Volatile Fuel Air Atmospheres "

PHONE (512) 858-4045; FAX (512) 858-4340; TOLL FREE IN USA 800-350-5105

website http://www.amptec.com e-mail [email protected]

TABLE OF CONTENTS

_______________________________________________________________

SECTION A: RECEIVING AND INITIAL INSPECTION

A-1 Introduction to the AMPTEC 620A 4

A-2 Receiving, Unpacking, and Initial Inspection

A-3 AC Battery Charger- Power Requirements

A-4 Setup and Use

A-5 Serial Number, Revision and Safety Board Approvals

SECTION B: 620A 4 IGNITER TESTER /

FAILSAFE OHMMETER SPECIFICATIONS

Table B-2. Specifications

SECTION C: OPTIONAL ITEMS AND ACCESSORIES

C-1 Available Accessories and Options

C-2 Test Lead and Probe Sets

SECTION D: OPERATION AND USE

D-1 General

D-2 Front Panel

D-3 Rear Panel

D-4 4-Wire Resistance Measurement

D-5 Connections

D-6 Failsafe Operation

D-7 Battery Monitoring Circuitry

Figure D-1. Error Sources in Resistance Measurements

SECTION E: THEORY OF OPERATION

E-1 General

E-2 Troubleshooting

E-2-1 Localizing the problem

E-2-2 Component Replacement

E-3 Circuit Description

E-4 Analog-to-Digital Converter

E-4-1 Reference Voltage

E-4-2 LED Display

E-5 Ohms-to-DC Converter

E-5-1 Constant Current Source

E-5-2 Constant Current Circuit Operation

E-6 Failsafe Design

E-7 Ultra-Safe Power Supply Scheme

SECTION F: ROUTINE MAINTENANCE

F-1 General

F-2 Required Test Equipment

F-3 Calibration Procedure

F-4 Battery Replacement Instructions

E-8 Relay Board General Operation

A-1. Introduction to the AMPTEC 620A-4

The AMPTEC 620A and the 630 Series Igniter

Testers/Failsafe Ohmmeters have become the

standard in the Safety Igniter Circuit Test

industry, and are designed to provide extremely

safe and reliable resistance testing of electrically

explosive devices (EEDs) or “current sensitive”

blasting devices. Approvals from various Safety

Boards include, the U.S. Air Force ( 620A-4) for

use on Non-Nuclear munitions provided the

appropriate T.O. is available. In addition the US

NAVAL ORDNANCE CENTER has approved

the AMPTEC 630AN, 630BN and 640N Igniter

Testers and other versions are pending. Some of

the devices the 620A Failsafe Ohmmeter may be

used on include: fuses, squibs, igniters,

warheads, explosive bolts, rocket motor squibs,

drone parachute squibs, automobile air-bag

initiators and many others.

The AMPTEC 620A-4 is a 4-wire Kelvin (i.e.

eliminates contact resistance errors) failsafe

digital ohmmeter which has been designed to

use safe levels of DC current for its DC

resistance measurement. Failsafe Output

Circuitry proprietary to AMPTEC RESEARCH

ensures that test current levels do not exceed the

specified "failsafe current" in a worst-case

component failure situation. The failsafe feature

is tested in every instrument before shipment.

The AMPTEC 620A-4 represents the latest in

ultra-safe Igniter Tester measurements. The

620A-4 (serial numbers 620A4-800 and higher)

Igniter Testers all use the same main printed

circuit board (PCB) referred to as Revision D.

Please check the Appendix of this manual for

any addendums that may apply to any

differences between the newer (rev D.) version

620A-4s and older (rev C.) 620A-4 Igniter

Testers with serial numbers less than 620A4-800

(i.e. 620A4- 525).

Should the rechargeable batteries reach a low

charge level, a minus sign will appear on the

display. The 620A-4 has a battery monitoring

circuit that indicates when to charge the

batteries.

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 620A 4 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.

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 number

(Return Material Authorization). 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. After getting an RMA #

from AMPTEC, as an added precaution against

loss, be sure to also affix an ID label (contact

info) on the lid of the 620A Igniter Tester with

your phone number, name, address and FAX

number, and email address. By calling

AMPTEC RESEARCH, prior to returning

the 620A, we can often troubleshoot and

identify the problem (i.e. battery loose in the

battery holder), over the phone.

A-3. AC/DC Battery Charger - Power

Requirements

The AMPTEC 620A 4 uses an internal

rechargeable heavy-duty nickel-cadmium

battery pack (4 D cells - 5.0 AHr). Replacement

batteries may be purchased, contact the sale

department at AMPTEC RESEARCH.

The battery charger is an external AC/DC

converter that plugs into a standard 115VAC

receptacle. The battery charger outputs 6.0

VDC @ 100 mA. The battery charger circuitry

is configured such that the 620A-4 main power

switch must also be in the “OFF” position.

The 620A-4 main power “On/Off” switch

design makes it impossible to be powered (in

operating - measurement mode) directly from

the AC/DC Battery Charger. When the 620A-4

main power switch is in the “On” position the

rear panel charging jack is electrically

disconnected from all 620A 4 circuitry.

A fully charged battery pack typically powers

the 620A 4 for approximately 8 hours before

requiring a recharge. AMPTEC installs a quality

set of 4 each Heavy Duty (5000 mAHr) Ni-Cad

batteries ( option 620-BAT) set of 4 ea.. The

620A 4 will also operate on a 4000 mAhr D cell

Ni-Cads with a shortened operating time

between charges. Recharge time is typically

twice the “Power On” time. An “Overnight”

charge usually restores the 620A 4 to a “Fully

Charged” ready to use state.

If you turn on the 620A-4, and the display does

not come on, it may indicate the batteries need

charging.

The diagram on the right shows a rear panel

view of the 620A Igniter Tester. To check the

fuse, remove the cap from the fuseholder. The

620A uses a 2 ampere fast blow (3AG size).

Only replace with an identical rated fuse.

A spare or replacement battery charger (option

“620-DC”) or replacement set of 4 each heavy

duty NICAD batteries (option "620-BAT") may

be purchased if needed, contact the sales

department at AMPTEC RESEARCH.

The “OFF/ CHARGING” power switch position

is for use when the batteries need charging or

the 620A-4 is not in use. As mentioned earlier

the Battery Charger (115 VAC 60 Hz powered )

must be plugged into the 620A-4’s rear panel

charging jack to facilitate charging the batteries.

Although the batteries are fully charged prior to

shipment, it may be desirable to refresh the

charge for 24 hours before use. As a rule of

thumb, the 620A requires twice as much time to

fully recharge as the amount of discharge time.

For example, if the instrument was used

continuously for 2 hours, the AC adapter must

be connected for 4 hours in order to fully restore

the charge.

use Ho de w th F seF lriu

ha i ck

Crg ng Ja

620A Battery Charger

Option "620-DC"

Additional note - Main switch Power “On”. When

the 620A Igniter Tester is first turned on, the unit

briefly draws more internal power then cuts back

to less than 100 mA, after a few seconds. The

initial Power “On” battery drain is to heat up the

unit’s ovenized zener voltage reference. If the

“Low Battery” Indicator only comes on (i.e. 10 to

15 seconds) for a few seconds (i.e. when the 620A

is first turned on), then goes out, the battery levels

are starting to indicate the charge level is starting

to get low.

A-4. Setup and Use

Once the AMPTEC 620A has had it’s batteries

charged for 12 to 24 hours it is ready for use. The

620A 4 only draws a little electrical power

(internal battery based) 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.

You may also have a test procedure or technical

order (T.O.) that has you inspect the calibration

sticker on the AMPTEC 620A Igniter Tester to

determine that it is still valid, or within its

calibration interval. Avoid exposing the 620A to

extreme temperatures, hot or cold which will affect

accuracy and shorten battery life-span.

A-5 Serial Number , Revision and Safety Board

Approvals

The AMPTEC 620A Igniter Tester represents the

latest in ultra-safe Igniter Tester resistance

measurements. The AMPTEC 620A-4 (serial

numbers 620A4-800 and higher) Igniter Testers

use the same main printed circuit board (PCB)

referred to as “Revision D”. This manual is

specific for the “Rev D” versions of the 620A.

Please check the Appendix of this manual for any

addendums that may apply to any differences

between the newer (Rev D.) version 620A-4s and

older (Rev C.) 620A-4 Igniter Testers with serial

numbers less than 620A4-800 (i.e. 620A4- 525).

The AMPTEC 620A-4 Igniter Tester is Mil Std

810 Method 511 Compliant for use in Explosive

Atmospheres Use to +50 degrees C . A copy of this

Approval and others is available in the password

protected section of AMPTEC RESEARCH'S

Certified for Use in Explosive Fuel Air Mixtures per

Mil Standard 810 Method 511.

A copy of this Approval and others is available in the

password protected section of AMPTEC

RESEARCH'S website www.amptec.com/tech.htm

. At present you must enter the following for access

User ID=2004 and the password=safety.

A variety of USAF Tech Orders related to the

AMPTEC 620A-4 are available there for review.

Contact AMPTEC RESEARCH if the password has

changed.

SECTION B - 620A 4 TESTER 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)

20 ohm through 20Kohm ranges . . . . . . . . . . . . . . . . ±0.02% of reading ±0.02% of range

(i.e if you a using a 10.000 ohm Resistance Std. - the high limit for the 620A-4 is a ohm reading

and the low limit is ohm reading )

Temperature Range

Operating 0°C to 50°C

Storage -10°C to 70°C

Temperature Coefficient

20ohm through 20Kohm ranges ±0.002% per °C (from 0°C-15°C and 35°C-50°C)

Test Current Level

(Model 620A-4 version) 20ohm range is <5mA when operating normal, <8mA worst case when faulty

Instrument Display . . (20,000 count) 4½ digit Super Bright Light Emitting Diodes (LED)

Over-Range Indication . . . . . . . . . . . . . . . . ( select next higher range) 620A 4 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 . . . . (4 "D" 5.7AHr Heavy Duty) 1.2V rechargeable nickel-cadmium batteries

AC/DC Battery Charger (Option DC) provides 6VDC at 100mA nominal

Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.5" (24cm) W x 11" (27cm) D x 3"(8cm) H

Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 lbs net; 6.5 lbs shipping (not counting transit case and

accessories)

AMPTEC RESEARCH continually strives to make improvements with it's instrumentation and as such reserves the right for

general operation of its products and specifications to be subject to change on rare occasion.

C-1. Available Accessories and Options

Listed below are the options available for use with the

AMPTEC 620A Series FailSafe Ohmmeters.

Option 620-DC: Battery Charger

Option "DC" is an AC/DC converter that converts

115VAC line voltage to 6VDC at 300mA. One charger

is provided as a standard accessory with every 620A. A

220 VAC 50 Hz powered Battery Charger adapter is

also available.

Replacement Batteries (Option 620-BAT)

The rechargeable Nicad batteries installed in the 620A

should provide years of trouble-free operation.

Replacement, however, will eventually be necessary.

The 620A uses four 1.2V cells (Heavy Duty) installed

in the units battery box. The batteries are held in place

by reusable tie-wraps. When ordering replacement

batteries, please specify AMPTEC option "620-BAT"

(a new set of 4 each NiCAD D cells will be supplied).

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.

Test Leads and Probes - All AMPTEC Igniter Tester

Leads and Probe sets are a minimum 48" length, (call the

Sales Department for any custom requirement).

Option “620RACK”: Rack Mount Adapter

Option "620RACK" includes an adapter tray that

allows any single AMPTEC 620 series tester to

be flush panel mount installed in a standard 19"

equipment rack.

C-2. Test Lead Sets and Probes

Option “290" Alligator Clip Lead Set

Option "290" is the recommended general

purpose Alligator Clip test lead set (red and

black) for models not having a 2.0 Ohm range

(due to a small resistance “offset” at the tips -

OK for 20 Ohm and higher range units ) . Option

“290" is supplied as a standard item with all

620A-4 (USAF version) ohmmeters as part of

the accessory package. Option “290" is a 48"

long cable set with dual banana plugs at one end.

The other end is terminated with an alligator clip

( red and black) . Some “Squib Resistance” test

panel jacks have a plastic exterior with a

conductive socket center. These alligator clips

will measure (2 wire method) properly with

either upper or lower jaw connected to the

conductive socket center of plastic test panel

jacks. Kelvin Clips see Option “300” (using the 4

wire method) may have difficulty only if both

jaws (both upper and lower) do not make

electrical contact with the conductive “resistance

under test” center.

See next page for Kelvin Clips and other

accessories.

SECTION C OPTIONAL ITEMS AND

ACCESSORIES

Option 401: Handheld Single Probe Leads

Option "401" is a gold plated 620 series compatible

handheld probe (one black probe & one red probe ) lead

set terminated in single points. The OP401 handheld

probes allow for easy access to connector socket wiring

(i.e. drone parachute squib sockets), recessed surfaces,

and parts (i.e. flares) that alligator clip can't reach.

Option 430 4000-ITS Mating Connector

AMPTEC offers an adapter connector that provides

equivalent circular socket connections (J9 Connector)

found on SIMPSON 4000 ITStm, and Alinco 101 series

Circuit Igniter Testers. In some applications (i.e. AIM-7

Missile harnesses) regular alligator clip leads cannot

properly connect to ( screw on ring collar type

connectors) the small recessed electrical sockets inside a

connector harness that normally mates with the J9 style

connector. This item is included in the AMPTEC 620A-

4 NSN 6625-01-460-1499NM package. The “OP430” has

the AMPTEC 620A Ohmmeter act as a 2-wire ohmmeter

from the OP430 connector out to the resistance under test.

Option "247" - Isolated Continuous Operating Power -

Allows the AMPTEC 620A series tester safely operate

continuously 24 hours a day 7 days a week. It includes an

isolated AC/DC wall adapter. This option uses a 3.0 KV

AC and DC isolated circuitry (i.e. medical grade DC to

DC convertor) to safely supply the 5.0 VDC need to

operated the units main measurement electronics

normally supply by batteries. This 3 KV medical grade

electrical isolation is the same safety isolation that cardiac

monitors use. That is they are AC line powered (i.e. 120

VAC) while electrodes are connected to a human patients'

chest. The unit’s Safety Board Approved failsafe ohmmeter

current source is still running independent of the meter’s 3.0

KV DC supply isolation circuitry. UL 61010 AC Line Isolation

Test Report confirms Isolation to 3 KV AC input protection.

Option “500” Optically Isolated Analog Output

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 purposes with an external device (i.e chart

recorder, system DMM with GPIB). Isolation protection

is rated @2000 volts peak to insure any instrument con-

nected to "Option 500" has virtually no impact on the

620 series tester's safety.

Option 300: 4-Wire Gold Plated Kelvin Lead Set

Option "300" is a general purpose Gold Plated

Kelvin four wire Leads for all AMPTEC 620 series

Testers. Kelvin clips provide a 4 wire Kelvin Gold

plated low thermal EMF connection (minimizes the

thermocouple effect) with most connections. The

Option “300” is the recommended test lead set for

any AMPTEC 620 Series Igniter Tester for

calibration or precision measurements (i.e

AMPTEC 620ES and 620RK). The 4 wire Kelvin

connection is important when measuring less than

1.0 ohm, and also automatically eliminates test

lead length offset and test lead contact resistance

errors. Option “300” is a shielded 48" lead set

terminated in ½" opening gold plated Kelvin clips.

The option "300" can clip easily to wires, pins, and

medium size (up to ½" diameter conductors). The

dual banana plug ends connect directly to the 620

tester's front panel input terminals. (see Option

"320" for replacement Kelvin clip ends only)

Option 305: Banana-to-Banana Cable

Option "305" is a 48" shielded cable terminated in

dual banana plugs at both ends.

Option 320: Kelvin Clips

Option "320" are the gold plated kelvin clips used

on the Option "300" cable set . These clips may be

used when making custom cables or when repairing

Option "300".

Option 360: Heavy-Duty Clips

Option "360" are Gold-plated jumper cable (large

jaws) type clips used on the Option "350" cable.

They are still Kelvin Clips because the insulated

upper and lower jaw (jumper cable appearance)

integrity is maintained. These may be used when

making custom heavy duty cables that open to 1

1/2 " wide (i.e bolt heads)..

The AMPTEC 620A-4 ohms ranges are

manually selected by pressing the desired range

switch on the front panel. The range select

pushbutton for the

lowest resistance range 20 Ohms ( leftmost

resistance range button) indicated above the

range select buttons. When a given range is

selected (pushed in) the other range switches

"pop-out" and inform the user. It is obvious to

the 620 user which resistance range has been

selected, as it is pushed in. Also note that a

resistance range should be selected after

powering up the 620A-4 in order to place it in

an operational mode. After turn "ON", a range

should be selected. 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". If

the front terminals are disconnected, the

display may even wander around, this is normal

for the disconnected 4 Wire Kelvin "Open

Circuit" mode.

D-3 Rear Panel

Fuseholder

The fuseholder is mounted on the rear panel of

the unit. The fuse for ithe AMPTEC 620A-4 is

a 2 ampere fast blow 3 AG type ( 1 ¼" long) .

This fuse is designed to protect the battery pack

from excessive currents. On some AMPTEC

620A versions a fuseholder is mounted on

D-1. General Operation

D-2. Front Panel Features and Operation

OFF

Range Switch

This section contains operating instructions for the

AMPTEC 620A4 Explosive Safety Igniter Tester. A

description of the front panel controlsm, connection

instructions and theory behind 4-wire Kelvin

resistance measurement is discussed in this section .

When the front panel power switch is in the “ ”

or charging position, all power is removed from the

(output terminals) ohmmeter measurement circuitry

and the unit's internal battery pack is connected to

the rear panel charging jack

When the AMPTEC 620A-4 main power switch

(single throw double pole) is placed in the " " or

up position, the battery pack is disconnected from the

rear panel charging jack. The possibility of a voltage

between the device under test and a AC/DC Voltage

from the rear panel AC/DC Charging jack is

therefore eliminated. The operator need not be

concerned if the battery charger is plugged in while

making resistance measurements.

(see diagram on next

page).

AMPTEC 620A-4 Range Switches shown

Option "620-DC"

SECTION D - OPERATION AND USE

OP247 AdapterOP247 Adapter

RS232C

Interface

revision 2.0

FUSE - 2 ampere

3AG FAST BLO

CAGE CODE 1CRL2

PHONE 800-350-5105

MADE IN USA

www.amptec.com

RESEARCH

AMPTEC

MODEL NUMBER 620A4

AMPTEC 620A-4 REAR PANEL configured with Option "232" , "247"

(not part of NSN 6625-01-460-1499NM package)

SERIAL NUMBER 620A4-1278

VHI VLO IHI ILOVHI VLO IHI ILO

620A4 Rear Panel with options RS232C I/O

The AMPTEC 620A4 rear panel (shown above) may

contain many optional jacks, terminals, labels, and

stickers. Only the option "247" Continuous Isolated

Operating Power DC Adapter (item #1) plugs in the rear

panel jack for isolation and in order to continuously

operate the unit.

Item 2 is the fuse holder - replace with a 2 ampere 3 AG

type fast blow fuse (rarely needs replacing).

RS232C Serial Interface - Item # 3 is the safety isolated

RS232C serial I/O (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 (Option 232 )

(NOTE: All front panel range buttons must be de-

selected (press in half way) with all range pushbuttons

out in order to disable with local lockout and enable

RS232C control. 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).

r0De-Selects all Ranges

r1 Selects the 20 Ohm Range

r2 Selects the 200 Ohm Range

r3 Selects the 2K Ohm Range

r4 Selects the 20K Ohm Range

VVersion commands board to output the firmware

version string.

CERTIFIED BY

DATE

CALIBRATED DATE DUE

AMPTEC 620A4

23JUNE2004 23JUNE2005

DWH

Serial # 620A4-1278

14 5

Data Format - The RS232C I/O outputs a data

string with the following format:

1.2345E+3 The measurement is always in Ohms

(where E+3 = 10 scientific notation style) . The

Exponent is defined below. 1.2345E+3 = 1.2345

KOhms (where E =10 ). 1.3700E+1 = 13.700

Ohms (where E =10 )

Range Exponent

20.0 Ohm E+1

200.0 Ohm E+2

2.0 K Ohm E+3

20 K Ohm E+4

An overrange condition 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 AMPTEC 620A-4 Voltage High,

Voltage low, Current high and Current low wires

are permanently connected to the gold plated rear

terminal strip ( seel 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

620A4 Explosive Safety Ohmmeter/Igniter Tester.

contact AMPTEC customer service 001-512-858-

4045 .

The battery charging jack is a barrel type and is

located on the 620A rear panel. The center pin

of the connector is positive. The charging

requirements of the internal battery pack are

6VDC @300mA. The correct charging voltage

is supplied by the adapter included with the

instrument. Additional AC/DC Battery

Chargers are available as Option "620-DC".

The four-terminal configuration of the 620A

eliminates errors normally caused by in series

test lead resistance and contact resistances. In

many applications the contact resistance can

exceed the value of the load by several orders

of magnitude.

The 620A avoids this potential error source by

providing two terminals of constant current and

an additional two terminals for high impedance

voltage measurement. The constant current can

be thought of as a that overcomes

lead length resistance and contact resistance

encountered (all series resistance) along its loop

path. The result is a fast, accurate resistance

measurement of the load, independent of the

resistance of the current carrying leads.

Figure D-1 (above) illustrates the 4-wire

principle and how it is used to eliminate lead,

wire and contact resistances as potential error

sources. The internal current source inherently

overcomes all series resistance (within

compliance voltage limits) and delivers a

precise constant current.

The internal high-impedance DVM senses the

voltage drop across the load. 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 leads.

Charging Jack

D-4. 4-Wire Resistance Measurement

with the AMPTEC 620A-5, the

charging jack is mounted on the unit’s front

panel.

current loop

Figure D-1. Error Sources in Resistance

Measurements eliminated with Four Wire

Kelvin Connections

Connections are made to the front panel

terminals using a 4-wire configuration as

described in section 4-4. When using AMPTEC

test leads, the tabbed or

. This ensures that the

current is carried in the largest conductor and

that the voltage input is shielded. The 620A

features five way gold plated input jacks. The

gold plating on the input jacks helps minimize

thermal EMFs . Wire connections often generate

a DC offset voltage with the contact between

two dissimilar metals (also called the thermo-

couple effect).

In addition, the 620A five way input jacks allow

for clean, simple connections to bare wires,

cables terminated with spade lugs, and banana

jacks.

D-5. Connections

negative (-) side of the

banana jack is plugged into the current

terminals of the 620A

620A CLOSEUP - INPUT JACKS (4 wire connection)

*contact resistance

.8V C

LIMITED

CONSTANT

CURRENT

SOURCE

VOLTAGE

LIMITING

RESISTOR

IGNITER

CurrentLoop

LEAD RESISTANCE

FAIL-SAFE

OHMMETER

DIG TALVOLTMETER

Ihi

Vlow

V high I high

V low I low

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).

Unless it is receiving a definite input signal,

the output reading of this A to D is

ambiguous. The display may indicate a

randomly wandering number or it may

indicate an overrange condition. This

unpredictable display may make it seem to

appear that the instrument is experiencing

some sort of malfunction. It is, in fact, just a

characteristic of the voltmeter circuit and

should not be mistaken for a fault in the

instrument.

The display indications should be ignored

unless there is a definite measurement being

taken. If this wandering display is not

acceptable, the ohmmeter can be made to

indicate an overrange condition whenever

the terminals are open by using a 4-wire

Kelvin type lead set or by shorting the VHI

and IHI terminals together.

The 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 a load,

recheck the test leads for integrity and

cleanliness. If all external items appear to

be functioning properly, the problem may be

the ohmmeter. In this case, please contact

your local AMPTEC RESEARCH Sales

Office.

D-6. Failsafe Operation

The AMPTEC 620A Series Igniter

Tester/Ohmmeter incorporate a proprietary

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

under the corresponding range switch on the

620A front panel. Please refer to section 5-6

for a technical description of the failsafe

circuitry.

Every 620A Series Failsafe Ohmmeter is

thoroughly tested before it leaves the

factory. Every resistance range is tested and

calibrated (a U.S. N.I.S.T. Certificate of

Calibration accompanies every 620A).

As a further precaution the 620A is isolated

from the AC line whenever the POWER

switch is in the ON position.

The 620A receives its power from an

internal rechargeable battery pack. The

620A must be in the OFF/CHARGING

position in order to charge the batteries.

D-7. Battery Monitoring Circuitry

If the low battery indicator LED is

continuously illuminated, readings should

not be trusted. An overnight recharge

should be performed before using the 620A

for critical testing.

It is possible for the user to receive a low

battery indication on a single range only

(particularly the 20 ohm range), while the

620A remains well within operating limits

on other ranges. Unless the user observes a

continuous low battery indication during

measurement, readings are still valid.

Notice for Cal Lab: The variable

potentiometer - trimpot RV3 is factory

adjusted to have the low battery indicator

come on at 4.50 VDC. To make this

adjustment, refer to Section F Routine

Maintenance for further details.

Replacing the AMPTEC 620A-4 Handles

The AMPTEC 620A-4 handle access screws are

located behind the black circular end caps (see

points A and B in the diagram below) at the joint

where the handles meet the case. Once the recessed

circular end caps have been removed (ie pop out with

screw driver), you should be able to locate the spring

loaded assembly with the access screws. Care should

be taken when unscrewing the handle access screws as

they hold back the spring loaded lock-notch assembly.

Once the screws have been removed the spring loaded

handle lock assembly will come apart (take note of the

parts and sequence of disassembly). Remove the

broken handle and replace with the new handle.

Return the spring loaded lock-notch assembly to the

center of the rotating joint (points A and B below).

Replace the retaining screws back into the center of

the spring loaded lock-notch assembly. Replace the

black end caps. The repair is complete.

Rotating the AMPTEC 620AInstrument Case

and Handle Position

The AMPTEC 620A-4 handles position can be

easily adjusted or rotated with the simple

maneuver described below. There is a lock

notch rotating joint at points A and B below,

where the handles meet the case. Never force

the handles to rotate as this will damage the

lock notch rotating joint and break the handle.

By pulling outward firmly but not too hard, you

can release the lock rotating notch mechanism

inside the handle pivot assembly. While pulling

out at points A and B, rotate the handle position

to the desired location. If the handles do not

freely pivot/rotate, then slightly more pulling

force at points A and B may be required (in

order to unlock the notch mechanism). Once

you have rotated the handles to the desired

angle simply release the outward pull at points

A and B. You should then feel or hear a "click"

as the handles lock/notch into the new position.

SECTION E - GENERAL OPERATION AND DESIGN

E-1. General

The AMPTEC RESEARCH 620A-4R Igniter

Tester is shown in block diagram form in Figure

E-1. All diagrams and information disclosed in

this chapter is proprietary and is included in

order to make troubleshooting to component level

possible.

The AMPTEC 620A 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 spare parts inventory of all

components found in the 620A Tester and it’s

customer service department can also provide

additional assistance in the trouble shooting

process.

E-2. Troubleshooting

Since the 620A 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 620A

Tester should not even attempt to remove the

calibration access screws or open the main

panel or effect any repair whatsoever.

Apparent 620A 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 620A series igniter tester .

If you turn on the AMPTEC 620A-4R, and the

display does not come on, it may indicate the

batteries need charging, or fuse needs replacing.

If the 620A-4R 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 Section of the 620A 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

620A Tester does not come on when powered

up, did you check the front 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 620A series 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 620A series igniter tester can be

maintained only if the 620A is re-calibrated

following the 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

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