AMPTEC igniter testingsquib testingpyrotechnic resistance measurementfailsafe ohmmeter

Safe Resistance Testing of Igniters, Squibs and Pyrotechnic Devices

Test current never exceeds 8 mA under any fault. When you measure resistance on bridgewires, detonators and explosive bolts, the instrument's safety ceiling matters more than its resolution.

Pyrotechnic work area inside a satellite integration facility

In short

For igniters, squibs, bridgewires and detonators, the first specification is not accuracy but failsafe current: under any single fault, the current delivered to the device under test must stay below the ignition threshold. The AMPTEC 620A-4 and 620UK-V4 set the laboratory standard with 4-wire Kelvin measurement, ±0.02% accuracy and an 8 mA failsafe ceiling; the 620UK-V4 also meets ATEX and intrinsic-safety requirements for use in volatile atmospheres. For field and range work there are the ruggedized, waterproof 620A-4R, 630BN and 641RS, and the 601ES safety multimeter handles the stray voltage and current check. Evencat is the sole distributor for AMPTEC in Taiwan and also rents igniter testers.

Why an ordinary ohmmeter must never touch an igniter

A bridgewire igniter works by passing current through a fine wire until it reaches ignition temperature. The test current an ordinary multimeter injects on its resistance range can sit right next to that threshold. So the first question in any electrical check of a pyrotechnic device is not "how accurate is it" but "what is the most current this instrument can push into the device under any fault condition".

That is the design premise of a failsafe ohmmeter: a current-limiting network holds the ceiling through any single component failure, and the open-circuit voltage is held at roughly 1.6 V. Across the AMPTEC line the maximum failsafe current is 8 mA, and it drops further by range to 1.5 mA, 150 µA and below. The higher the range, the lower the current.

The laboratory standard: 620A-4 and 620UK-V4

The 620A-4 is AMPTEC's flagship digital failsafe ohmmeter. 4-wire Kelvin measurement removes lead resistance, all four ranges from 20 Ω to 20 kΩ hold ±0.02% of reading and of range, the 20 Ω range resolves 1 mΩ, and the temperature coefficient is ±0.002% per °C. It is approved by the US Air Force Non-Nuclear Munitions Safety Board and used by NASA and the USAF, which makes it the standard tool for firing-circuit acceptance and lot inspection.

The 620UK-V4 is the portable EEX unit. Its ranges extend from 2 Ω to 2 MΩ, its failsafe current limiting meets the EU ATEX directive and the intrinsic-safety standard Eex-9b-IIc-T4, and it passes MIL-STD-810. When the test location is itself a volatile atmosphere, such as a loading bay or a propellant workshop, this is the instrument you need.

Field and range work: the ruggedized units

Flight deck operations on an aircraft carrier at sea — Shipboard and test-range work

Outside the lab it rains, things vibrate and there is electromagnetic interference. The 620A-4R keeps the 620A-4's internal circuit and adds a waterproof, weather-resistant enclosure, a built-in Faraday cage and a wide-angle tilted LED display, with accuracy still ±0.02%. The 630BN was developed for a US military ordnance program (NSN 6625-01-587-4854); it integrates a self-contained DC milliammeter and test resistor, adds diode testing, and suits in-circuit measurement of bridgewires, fuzes and explosive bolts.

The 641RS is the compact ruggedized unit: eight ranges cover 2 Ω to 20 MΩ, a built-in self-test and a precision test resistor let the operator verify the instrument in the field, and it is 40% lighter than the previous 640 series. All three cap failsafe current at 8 mA.

Check for stray voltage before you measure resistance: 601ES

Before an ohmmeter is connected to a firing circuit, the correct procedure is to confirm the circuit carries no stray voltage or current. Static charge, induced voltage or a ground loop can all flow through the bridgewire the instant the leads touch. The 601ES is a weatherproof, intrinsically safe digital multimeter that measures 2 to 600 V AC/DC, 2 A AC/DC and resistance from 2 Ω to 20 kΩ, again with an 8 mA failsafe ceiling. It has a waterproof enclosure, conformal-coated circuitry and an all-metal Faraday cage, passes MIL-STD-810 explosive-atmosphere compliance testing and carries UL-913 certification.

Purchase, rental and calibration

Evencat is the sole distributor for AMPTEC Research in Taiwan and can speak directly to the certification documents, calibration certificates and lead time of each model. For project-based acceptance testing or short range campaigns, igniter tester rental gets equipment on site first; for long-term users we recommend choosing a laboratory or ruggedized model to match the working environment and planning annual calibration.