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620A-4 | Digital Failsafe Ohmmeter

The 620A-4 Igniter Circuit Tester is our flagship ohmmeter. A failsafe and portable digital ohmmeter specifically designed for ultra-safe resistance testing on squibs, flares, bridge-wire, and other explosive devices, the 620A-4 was the first we designed in our long line of intrinsically safe instruments. Capable of making highly accurate resistance measurements from 20 Ω to 20 KΩ, this ohmmeter has a proven track record of durability: with 20+ year old units still being used in the field today. This unit has been designed to never have a current level that exceeds 8 mA – the cornerstone of our failsafe design. The 620A-4 is compatible with many convenient modifications, such as OP-247 Optically Isolated Power (enabling the unit to run on AC power rather than batteries) or OP-232 RS232C Interface (enabling the unit to communicate with your computer via an RS232 port), allowing you to fully customize your instrument and cater it to your specific needs. Due to its intense self-safety design and numerous certifications, the 620A-4 failsafe ohmmeter is the industry standard for military programs in need of igniter testing.


The 620A-4 safety ohmmeter has been approved by the USAF Non-Nuclear Munitions Safety Board for usage on all non-nuclear munitions, and independently certified to meet Mil. Std. 810 Mtd. 511 for usage in fuel-filled environments. Amptec is an ISO 9001:2015 certified company, ensuring each instrument is manufactured to the highest quality standard.  Every instrument made is designed and manufactured in the USA, comes with an extensive one-year warranty, and an N.I.S.T. calibration certificate with data at no extra charge.


Please contact us to purchase.




Range, Resolution, Accuracy, and Current Levels

Range 20 Ω 200 Ω 2K Ω 20K Ω
Nominal Current 5 mA .5 mA 50 uA 5 uA
Failsafe Current 8 mA 8 mA 8 mA 8 mA
Resolution 1 mΩ 10 mΩ 100 mΩ 1 Ω
Accuracy ± .02% of reading & range ± .02% of reading & range ± .02% of reading & range ± .02% of reading & range


General Specifications

Display 4 1/2 digit LED Terminal Banana jack binding posts
Storage Temperature Range -20° to 70° C Operating Temperature Range 0° to 50° C
Dimensions 9.75″ x 10″ x 3.25″ Weight (Standard Version) 3.5 lbs.
Power 4 ea rechargeable 5AHr NICAD batteries Max. Input Voltage 250 VDC
Open Circuit 1.6 VDC Max. Internal Voltage 4.8 VDC
Update 3 readings/second Temperature Coefficient ± .002% per 1° C

For further specifications (such as the various modified versions of this product) contact us or see the product data sheet.

Ordering Information

The 620A-4 failsafe ohmmeter may be purchased as a part of two separate packages, which are listed below.
This product is unavailable for online purchase. For specific pricing information or to place an order for a 620A-4 meter, please contact us today.

Package Description Price
NSN Package Includes 620A-4 failsafe ohmmeter, (OP-100) transit case, (OP-290) leads, (620-DC) battery charger, (OP-430) connector adapter, & U.S. N.I.S.T Calibration Certificate. Request a quote!
Commercial Package Includes 620A-4 failsafe ohmmeter, (OP-300) leads, (OP-401) probes, (OP-110) lead pouch, (620-DC) battery charger, & U.S. N.I.S.T Calibration Certificate. Request a quote!
Lead/Probe Sets The 620A-4 ohmmeter is compatible with our 620 Series probe/lead sets and accessories. This product is also customize-able: it can be rack mounted, contain an RS232C interface, or use an optically isolated power source, for example. Contact us for more information.

For more detailed ordering information, contact us or see the product data sheet.

Compatible Accessories
Part Number Description Link
620-DC Battery Charger for 620 Series Igniter Testers Click Here
620-BAT Set of 4 NiCd D cell batteries Click Here
OP-100 Transit Case Click Here
OP-290 4′ Alligator Clip Lead Set Click Here
OP-300 4′ Gold Plated Kelvin Clip Lead Set Click Here
OP-304 4′ Banana Jack Calibration Lead Set Click Here
620 Series Leads The 620A-4 is compatible with our 620 Series probes and leads Click Here

For a more complete list of compatible accessories and modifications, contact us or see the product data sheet.