AMPTEC Research · Failsafe Igniter Testers
620LM
Failsafe wide-range ohmmeter with diode test, built for ultra-safe testing of explosive devices.
The 620LM is a failsafe ohmmeter for ultra-safe resistance tests on squibs, flares, bridge wires and other explosive devices. It descends from the 620A-4 approved by the USAF Non-Nuclear Munitions Safety Board (USAF NNMSB) and has become an industry standard for igniter testing. With a built-in diode test and six ranges from 2Ω to 20MΩ, it suits labs and engineering teams that need precise resistance readings under strict safety limits. Evencat is the sole distributor for AMPTEC Research in Taiwan.
Overview
The AMPTEC 620LM is a failsafe wide-range ohmmeter developed for ultra-safe testing of initiators, flares, bridge wires and other explosive devices. The design comes from the 620A-4 approved by the USAF Non-Nuclear Munitions Safety Board, has been used in THAAD-related munitions testing, and is treated as the industry standard for igniter work. Six ranges cover 2Ω, 20Ω, 2KΩ, 20KΩ, 200KΩ and 20MΩ through 4-wire Kelvin terminals, with ±0.02% of reading and range accuracy on the main ranges and a 4.5 digit LED display. The failsafe current is limited to 8mA on the standard ranges, so a fault inside the meter cannot fire the device under test. The unit also includes diode test, the RS232C interface (OP-232) and optically isolated power (OP-247) as standard, is built under ISO 9001:2015, is UL-913 compliant and is trusted by NASA and the USAF. Before ordering, decide whether you need the isolated analog output or the rack mount kit for a fixed test station.
Key specifications
| Resistance ranges | 2Ω, 20Ω, 2KΩ, 20KΩ, 200KΩ, 20MΩ |
|---|---|
| Nominal test current | 5mA, 5mA, 50µA, 5µA, 0.5µA, 0.01µA |
| Failsafe current | 8mA (standard ranges); 0.015µA (20MΩ); 25mA (diode) |
| Diode test | 0.5mA nominal; 25mA failsafe |
| Accuracy | ±0.02% of reading and range (most ranges); ±2% of reading and ±0.2% of range (20MΩ) |
| Resolution | 100µΩ to 1KΩ depending on range |
| Display | 4.5 digit LED |
| Terminals | 4-wire Kelvin |
| Maximum input voltage | 250VDC |
| Open-circuit voltage | 1.6VDC |
| Accurate temperature range | 0°C to 50°C |
| Update rate | 3 readings/second |
| Dimensions | 9" × 10" × 3" |
| Weight | 8 lbs |
| Power | 4 rechargeable 5AH NICAD batteries |
| Certifications | ISO 9001:2015, UL-913 |
Features
Failsafe design
The failsafe current is held within 8mA on the standard ranges, so even a fault inside the meter cannot fire the explosive device under test.
Wide-range measurement
Six resistance ranges from 2Ω to 20MΩ, with ±0.02% of reading and range accuracy on the main ranges, cover the full spread of igniter test needs.
4-wire Kelvin measurement
4-wire Kelvin terminals take lead resistance out of the reading, and resolution starting at 100µΩ supports precise low-resistance work.
Diode test capability
A built-in diode test (0.5mA nominal, 25mA failsafe) extends coverage to igniter systems that include a diode.
RS232C and optically isolated interfaces
The RS232C interface (OP-232) and optically isolated power (OP-247) come standard, easing data capture and system integration while protecting measurement integrity.
Industry-standard lineage
Derived from the 620A-4 approved by the USAF Non-Nuclear Munitions Safety Board, trusted by NASA and the USAF, built under ISO 9001:2015 and UL-913 compliant.
Typical applications
Missile systems
Pyrotechnic verification on the THAAD ballistic missile interceptor
During operational readiness work on the THAAD terminal high-altitude defense system, ordnance technicians use the 620LM for in-circuit resistance checks on squibs and bridge wires, confirming the firing loop is complete and free of shorts. The output current stays under 8 mA throughout, never approaching the no-fire threshold of the device.
Aircraft maintenance
Pre-flight safety checks on ejection seats and canopy cutters
Before each sortie, ground crews run non-destructive continuity and resistance checks on ejection seat cartridges, explosive canopy cutters and fire suppression bottles. The diode test in the 620LM also reads the forward and reverse behavior of protection diodes in the loop, confirming that the safety interlock has not been bypassed before the aircraft is released.
Ammunition storage
Routine igniter QC in magazines and ground weapons preparation stations
After batch receipt or long-term storage, weapons preparation stations sample the electrical condition of flares, smoke cartridges and fuze igniters. The 620LM sends readings straight to the QC system over its RS232C interface (OP-232) with optically isolated power (OP-247), meets MIL-STD-810F environmental requirements, and follows intrinsic safety practice for fuel vapor and similar hazardous atmospheres.
Options and configuration
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Standard equipment (included)
Hardware options
Downloads
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