The AMPTEC 620UK-B is a bonding milliohmmeter designed for safe and reliable low-level DC resistance testing, particularly on explosive or volatile devices. It is widely used in maintenance wings globally, having been originally designed at the request of Lockheed Martin's engineering team.
Function Description
The 620UK-B measures DC resistance using a 4-wire Kelvin (or 4-terminal ohms) technique. This method effectively eliminates measurement errors caused by the resistance of the test leads/probes and their contact resistance to the device under test. Two wires (current high and current low) pass through the bond resistance under test as part of a constant current source (100 mA). The constant current source's compliance voltage ensures 100 mA flows in the loop, regardless of lead length or contact resistance. The other two wires (voltage high and voltage low) sense the voltage drop across the resistance under test. This voltage measurement is high impedance, drawing virtually no current in the voltage sense leads. The meter then scales its display as resistance based on Ohm's Law (V/I=R). During a measurement cycle, the meter changes polarity, samples again, and displays the average reading of both polarities.
The device is suitable for:
- Electrical chassis ground connections and continuity determination on electrical subsystems in aircraft, helicopters, fighter jets, UAVs, drones, missiles, etc.
- Continuity determinations on fuses, electrical cable connections, and heavy-duty metal-to-metal connections.
- Bonding measurements for metal-to-metal connections.
Important Technical Specifications
- Resistance Range/Resolution:
- 200 mΩ range: 100 mA nominal current, 0.01 mΩ resolution.
- 2 Ω range: 100 mA nominal current, 0.1 mΩ resolution.
- Accuracy: ± 0.05% of reading for both ranges.
- Calibration: Recommended annually.
- Dimensions: 7.69" W x 7.56" D x 3" H.
- Hazardous Use Locations: UL-913 approved as intrinsically safe for Class 1, Division 1, Groups A, B, C, and D locations (ambient temperatures from -20° C to 50° C, T3 zones). MIL. STD. 810 MTD. 511 approved for use in explosive and volatile atmospheres.
- Instrument Display: 20,000 counts, 4 ½ digit liquid crystal display with a backlight that indicates autolock.
- Low Battery Indication: "LO BAT" displayed.
- Measurement Update Rate: Approximately 3 readings per second.
- Open Circuit Current Source Compliance Voltage: ~5.0 VDC.
- Over-Range Indication: "1 - - - -" and ">>>OR" displayed.
- Power: Four 1.5 VDC AA alkaline Duracell MN1500 batteries housed in a separate chemical and F.O.D. resistant metal battery box. Do not mix battery brands; replace all batteries simultaneously.
- Temperature Range: Operates from -20° C to 40° C at rated accuracy. Stores from -20° C to 70° C.
Usage Features
- Ease of Use: Features an all-metal case and a separate F.O.D. resistant battery compartment. Can be carried hands-free using the padded straps of its carrying case, allowing the user to focus on probe placement.
- Power On/Off: To turn on, press and hold the power switch for 2 seconds. This prevents accidental power-on. The LCD display and a small LED on the front panel indicate power is on. Pressing the switch again turns the unit off.
- Automatic Shut-off: The meter automatically turns off after 5 minutes of inactivity to conserve battery life. This feature can be deactivated upon request to AMPTEC.
- Autolock Feature: The meter senses continuity, automatically samples readings, and locks on the most accurate resistance measurement. It takes 16 positive polarity measurements, averages them, then 16 negative polarity measurements, averages them, and finally averages these two values for the final autolocked measurement.
- An audible beep and the lit backlight indicate an autolock measurement has been found, allowing the user to focus on probe placement.
- The display backlight turns off during the active measurement cycle and lights up when a measurement is locked.
- Measurements reset automatically if continuity is sensed again or by pressing the "AUTO MEASURE RESET" button.
- Resistance Range Selection: The meter starts in Auto Range. Pressing the "AUTO MEASURE RESET" button (when the backlight is off) cycles through Auto, 200 mΩ, and 2 Ω ranges.
- Test Lead Connection: Uses a 4-terminal-in Trident connector on the front panel. Only AMPTEC 620UK-B compatible test leads should be used to prevent damage to gold pins and sockets. The keyed access connector prevents incorrect lead/probe connections.
- Chassis Ground: A front panel chassis ground panel jack (accepts external banana jack) is wired to the all-metal case, front panel, rear panel, and battery compartment, as well as "pin G" of the test lead connector. This allows connection to an earth ground to preclude static voltages.
- Display Backlight: Yellow backlight illuminates when the unit is powered on and when an autolock measurement is achieved.
Maintenance Features
- Reliable Design: Built with high-quality, strong, and reliable internal and external components, making it extremely reliable and rarely in need of repair.
- Troubleshooting: The manual provides diagnostic test routines for the Current Source PCB and DVM PCB to help identify faulty circuitry.
- Calibration Adjustment: Two adjustment potentiometers (for zero and full-scale adjustments) are located on the DVM PCB, accessible through holes on the rear panel, under a tamper-proof calibration sticker. Removing this sticker voids the product's calibration and warranty.
- Zero Adjustment: Requires a precision 0.001 Ω (1.0 mΩ) resistance standard (0.005% or better). Adjusts a trim-pot to read the exact value of the 0 mΩ standard resistor.
- Full-scale Adjustment: Requires a precision 100 mΩ resistance standard (0.005% or better). Adjusts a full-scale pot to display the actual value of the 100 mΩ standard.
- The meter's autolock feature requires waiting 5 to 10 seconds between adjustments for settling and updated display.
- Recommended Calibration Standards: AMPTEC recommends using their 630-304 4-Wire banana jack test lead set and NIST-traceable resistance standards (e.g., from Ohm-Labs).
- Battery Compartment: Metal, powder-coated for chemical resistance, and backed with a watertight rubber-based compression gasket liner. Battery supply wiring insulation is extra thick Teflon for abrasion resistance.
- Battery Replacement: Requires removing two retaining screws on the rear panel's battery compartment cover. Use only AA alkaline (1.5 VDC) Duracell MN1500 batteries. Replace all four batteries simultaneously and do not mix brands or batches. Re-secure with a plastic cable tie or similar fastener. This activity does not interfere with warranty or calibration as the compartment is separate from internal electronics.
- Repair Services: AMPTEC RESEARCH provides maintenance, repair, and calibration services at their facility. An RMA number must be obtained before sending a unit for service. Diagnosis is free, but if internal circuitry access is required, a calibration fee applies as all instruments are calibrated before leaving the facility.
- PCB Removal (Discouraged): Removing the PCB voids the warranty and calibration. A detailed procedure is provided for authorized and trained personnel, involving removing front panel screws, carefully pulling the front panel forward, sliding out the display and main PCBs, disconnecting/reconnecting wires, and following calibration procedures. AMPTEC offers free PCB replacement for warranty products and a small fee for non-warranty products.
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