AMPTEC Research · Failsafe Ohmmeters
620A-4
Intrinsically safe digital failsafe ohmmeter for resistance measurement on igniters and explosive devices.
The Amptec 620A-4 is the flagship digital failsafe ohmmeter of the 620 series. With 4-wire Kelvin measurement it reads bridge wires, fuzes, flares and other explosive devices in ordnance environments, and its test current cannot exceed 8 mA under any fault. Accuracy of ±.02% on every range and long service with NASA and the USAF have made it the reference meter for ultra-safe resistance checks on munitions and firing circuits. Evencat is the sole distributor for AMPTEC Research in Taiwan.
Overview
The 620A-4 igniter circuit tester and failsafe ohmmeter is the AMPTEC flagship for resistance measurement on bridge wires, fuzes, flares and other explosive devices. The principle is failsafe operation: under any single fault the output current never exceeds 8 mA, which removes the risk of firing the device by measuring it. The meter offers four ranges of 20Ω, 200Ω, 2KΩ and 20KΩ, holds ±.02% of reading and range on all of them, and uses 4-wire Kelvin terminals so lead resistance does not enter the result. It is approved by the USAF Nonnuclear Munitions Safety Board for all non-nuclear munitions and qualified to Mil. Std. 810 Method 511 for use in fuel-laden atmospheres. Each unit ships with a one-year warranty and an N.I.S.T. calibration certificate, and units more than 20 years old are still in service. Before ordering, decide whether you need the RS-232C interface or the isolated AC supply for a fixed test station, and whether the ruggedized 620A-4R suits your site better.
Key specifications
| Measurement ranges | 20Ω / 200Ω / 2KΩ / 20KΩ |
|---|---|
| Accuracy | ±.02% of reading and range (all ranges) |
| Maximum failsafe current | 8 mA (never exceeded under any fault) |
| Resolution | 1 mΩ (20Ω range) |
| Display | 4 1/2 digit LED |
| Measurement terminals | 4-wire Kelvin (banana jack binding posts) |
| Update rate | 3 readings/second |
| Temperature coefficient | ±.002% per 1°C |
| Maximum input voltage | 250 VDC |
| Open-circuit voltage | 1.6 VDC |
| Power | 4 rechargeable 5AHr (5000 mAh) NICAD D cells with the 620-DC charger |
| Weight | 3.5 lbs |
Features
8 mA failsafe design
The output current stays at or below 8 mA under any fault, which is the foundation for measuring explosive devices without firing them.
4-wire Kelvin accuracy
4-wire Kelvin terminals take lead resistance out of the reading, giving ±.02% of reading and range on every range.
Four ranges
Ranges of 20Ω, 200Ω, 2KΩ and 20KΩ with resolution down to 1 mΩ cover bridge wire and fuze resistance checks.
Clear LED readout
A 4 1/2 digit LED display updates 3 times a second and stays readable in the field and in fuel-laden areas.
Military environmental qualification
Qualified to Mil. Std. 810 Method 511 for use in fuel-laden atmospheres, UL-913 compliant and built under ISO 9001:2015.
Rechargeable battery power
Four rechargeable 5AHr NICAD D cells inside a 3.5 lbs housing; units have logged more than 20 years of field service.
Typical applications
Aerospace and ordnance
Pre-delivery continuity checks on missile and rocket motor igniters
At USAF and NASA facilities the 620A-4 confirms squib and initiator resistance before assembly into missile, rocket and spacecraft propulsion systems, checking that bridge wire values sit inside tolerance while the 8mA failsafe limit rules out an accidental firing.
Explosive ordnance disposal
Fuze continuity verification by EOD teams in the field
Explosive ordnance disposal technicians use the 620A-4 before a task to measure continuity of bridge wire detonators, pyrotechnic tracers and other military initiators. Four NICAD cells power the portable meter, so checks run in hangars, magazines or field stations without an external supply.
QC acceptance
Incoming resistance sampling of pyrotechnic and safety initiators
Quality labs at arms manufacturers and defense contractors use the 620A-4 for batch sampling of pyrotechnics such as flares and ejection seat initiators. Four ranges (20Ω to 20KΩ) cover the resistance specifications involved, and ±0.02% accuracy under NSN # 6625-01-460-1499 procurement yields records that satisfy ISO 9001:2015.
Options and configuration
Tick the options you need. We compile the full configuration into a list and carry it into the quote form.
Standard package (included)
Hardware options
Model upgrade options
Downloads
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