Nato Stock Number 6625-99-833-7949

Download the Model 620UK datasheet (pdf format)

The 620UK Explosive Safety Ohmmeter
The 620UK Low Resistance Explosive Safety Ohmmeter is a portable digital, intrinsically safe, explosive safety ohmmeter which has been specifically designed for ultra-safe resistance testing on explosive devices (i.e. squibs, igniters, flares, detonators, warheads) in volatile and explosive atmospheres. The 620UK Ohmmeter features a pattern 104 - type 3 NATO Std. connector and is a direct replacement for the Fairey MK7 Safety Ohmmeter. The 620UK is manufactured in the UK by Permac Electronics and is approved by Sira Test & Certification to EEx ib IIc T4 (Certificate Number: Sira03ATEX2076). EMC tested in accordance with British Defence Standard 59-41 and complies with British Defence Standards 66-31, 07-85 and 05-34 (-40° Cold temperature, Damp Heat +°70C, Humidity and Altitude tests) . The 620UK Ohmmeter provides a reliable and safe means of measuring resistance in explosive and volatile atmospheres.

Intrinsically Safe Ohmmeter - EeX-ib-IIC-T4 British Defence Standard Compliant
There are a number of critical military, commercial aerospace and aircraft applications that use squibs, EEDs (electronic explosive devices), detonators, explosive bolts and a number of explosive/blasting devices. It is critically important that these devices detonate when properly triggered. It is also critically important that these devices do not detonate while being tested for wiring continuity/integrity. Each Safety Ohmmeter is manufactured with redundant, dual fail-safe protection - current limiting and resistor network circuitry that limits and ensures that the instrument test currents cannot exceed the specified amount. Even in the unlikely event of a worst case component failure, the output current limiting network is still in effect.

Low Ohm Range - Accuracy and Resolution
The 620UK offers the following full-scale ranges - 2.0 Ohms, 20 Ohms, 200 Ohms 20K Ohms, 200K Ohms and 2.0M Ohms. The 2.0 Ohm full-scale range provides a two-wire resistance measurement from 0.0000 ohms to 1.9999 ohms. The 2.0 Ohm range also offers a low (1/10) 0.1 milliohm or 100 micro-ohm resolution. The 2.0M Ohm range provides a relatively high resistance range for determining electrical isolation status or open circuit” (>2.0M Ohms) character of ordnance related control lines, pins, sockets and wiring.

Better and Safer than a Multifunction DMM
Multifunction DMM's have many modes (i.e. DC Voltage, AC Voltage, DC current, AC current, frequency, shift keys, Capacitance and more..) that can measure igniter circuit resistance incorrectly. If the DMM has an electrical fault the igniter circuit may accidentally fire. The 620UK Safety Ohmmeter only measures resistance, it is not a complex multifunction DMM. If the 620UK had an electrical fault it offers the life saving advantage of failing safe.

No Hazardous Mercury Batteries
The 620UK does not use hazardous mercury batteries like those in older model igniter testers. All 620UK Safety Ohmmeters are powered by 4 x AA Alkaline batteries.

Polyurethane Epoxy Coated Circuit Board and More ...
A common question we get from evaluating safety engineers is "What sort of electrical and mechanical measures are taken with the 620UK to prevent an internal loose wire, metal screw, or washer inside from floating around and shorting the battery output to the terminal output connections?". The ohmmeter's output connections are insulated inside the unit with heat shrink tubing covering any of it's conductive surfaces. The entire PCB (except for the calibration trim pots) is also non-conductive polyurethane epoxy coated, to make it extremely difficult to get an accidental conductive pathway. The ultimate electrical safety analysis for fail-safe current relies on "Ohms Law" for determining Imax, based upon a Vmax ( ~ 6.0 VDC battery value) divided by the equivalent circuit current limiting resistance (R-limit) for the particular version being considered. 620UK circuit schematics are available upon request for reviewing the maximum fail-safe current level.

Large 4 1/2 digit, high contrast LCD display, visible in direct sunlight (back lit for low ambient light conditions)

Specifications
Accuracy: (1 year 25°C ± 10°C) ± 0.02% of reading  ± 0.05% of range for 2.0 ohm range, ±0.02% of reading and range for 20 ohm through 20 Kohm range, ±0.05% of reading and range for 200 Kohm, ±1% of reading and ±0.2% of range for 2M ohm.
Display: 4½ digit (19999) L.E.D.  - 20,000 counts
Display visible day or night (back lit display)
Open Circuit Current Source Compliance Voltage: Diode clamped at <1.4V
Terminal Configuration: Two-wire
Operating Temperature Range: -20°C to +40°C
Temperature Coefficient: ±.01% per °C (from 0°C to 15°C and 35°C to 50°C)
Conversion Rate: Approximately once per 3 seconds
Calibration: Tamper Resistant Security Screws (1 year calibration interval)
Power: 4 x AA Alkaline batteries - good for one year
Max. Internal Voltage: 6.0 Vdc
Size: 235mm/9" D x 254mm/10" W x 76mm/3" H
Weight: 1.6 KG/3.5lbs NET 3 KG/6.5 lbs shipping