AMPTEC Research · Ruggedized Failsafe Ohmmeters
641N
Compact ruggedized failsafe igniter tester ohmmeter with self-test
The AMPTEC 641N is a ruggedized failsafe ohmmeter for military ordnance programs, used to measure the resistance of explosive bridgewires (EBW), fuzes, flares and similar explosive components without risk of firing them. It combines a shielded Faraday cage, a built-in DC milliammeter and test resistors, and a self-test function that was new with this generation. At 40% lighter than the 640N it replaces, it is the tool we recommend when safety and portability both matter in firing-circuit tests. Evencat is AMPTEC's sole distributor in Taiwan.
Overview
The AMPTEC 641N is a compact ruggedized failsafe ohmmeter built for safe resistance measurement on military munitions and explosive components. It tests initiators, flares and explosive bridgewires (EBW) with the failsafe current limited to 8 mA, so even an internal fault cannot push enough current into the device to fire it. The measuring circuit sits inside a shielded Faraday cage, with a built-in DC milliammeter and test resistors, a 4½ digit LED display and Trident terminals. The self-test function lets you confirm the meter is healthy in the field, and the waterproof compact case is made for rough outdoor and tactical conditions. Compared with the earlier 640N, the 641N is about 40% lighter and more self-aware. It is UL-913 compliant, built under ISO 9001:2015, and in service with NASA and the USAF. When ordering, choose your probe or lead set and consider the 641-DC charger and an annual calibration plan.
Key specifications
| Resistance ranges | 2 Ω / 20 Ω / 200 Ω / 2K Ω / 20K Ω / 200K Ω / 2M Ω |
|---|---|
| Accuracy | ± .02% (2M Ω range: ± 1% ± 0.2%) |
| Max failsafe current | 8 mA |
| Max input voltage | 250 VDC |
| Open circuit voltage | 1.6 VDC |
| Resolution | Down to 100 µΩ (2 Ω range) |
| Display | 4½ digit LED |
| Terminals | Trident |
| Power | 4 rechargeable 5AH NICAD batteries |
| Operating temperature | 0° to 50°C (temperature coefficient ± .002% per 1°C) |
| Dimensions | 10.62″ × 9.68″ × 4.87″ |
| Weight | 6.5 lbs |
Features
Failsafe design
The failsafe current is limited to 8 mA, so initiators and explosive components cannot be triggered even if the circuit fails; UL-913 compliant.
Self-test function
The built-in self-test, new with this generation, lets you confirm the meter is working in the field before the first reading.
Shielded Faraday cage
A shielded Faraday cage blocks external electromagnetic interference and keeps sensitive firing circuits protected during measurement.
Compact ruggedized case
The waterproof compact case suits harsh field and tactical use; about 40% lighter than the previous 640N, so it is easier to carry.
High accuracy
Seven ranges from 2 Ω to 2M Ω, accuracy ± .02%, resolution down to 100 µΩ, with a built-in DC milliammeter and test resistors.
Rechargeable battery power
Runs on 4 rechargeable 5AH NICAD batteries, so it works on site and in the field with no mains supply.
Typical applications
Military munitions
Munitions and igniter continuity acceptance testing
During munitions production and receiving inspection, technicians use the 641N to measure the resistance of bridgewires, squibs and flare firing circuits and confirm continuity within the ±0.02% specification tolerance. The self-test verifies the meter itself before each test, removing one source of human error from the pass/fail decision.
Launch preparation
Pre-launch firing circuit verification on NASA and USAF launch vehicles
Working through the pre-launch checklist on a rocket or missile, ground crews use the 641N to verify the resistance of each stage igniter. The Faraday cage shields the measurement from RF interference and electrostatic discharge, and the hardware limit of 8mA failsafe current guarantees the test current cannot initiate the charge, as NASA and USAF explosive-device test rules require.
Field maintenance
Ruggedized field maintenance of electro-explosive devices
In bad weather or at forward positions, the waterproof case and 0°C to 50°C operating range let the 641N deploy straight into the field. EOD and ordnance technicians use it for in-place resistance checks on flares, explosive bolts and canopy charges already installed on a system, confirming the device has not aged or taken on moisture without removing it.
Options and configuration
Tick the options you need; we will assemble the configuration list and carry it into the inquiry form.
Standard equipment (included)
Probe and test lead options
Charging and calibration service options
Downloads
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