AMPTEC Research · Digital Micro-Ohmmeters
720A
7-range 4-wire Kelvin digital micro-ohmmeter for precision low-resistance measurement from 10 µΩ to 200 kΩ
720A is AMPTEC Research's bench digital micro-ohmmeter. It uses a 4-wire Kelvin connection across 7 ranges from 200 mΩ to 200 kΩ, with best resolution of 10 µΩ. Engineers use it for winding resistance, contact resistance and component resistance where a low reading must be trusted. NASA and USAF safety approvals mean it is also accepted in ordnance and aerospace work that needs both accuracy and traceability.
Overview
AMPTEC 720A is a reasonably priced, fully featured 7-range digital micro-ohmmeter. A 4-wire Kelvin connection removes lead and contact resistance from the result, so low-resistance readings are accurate and repeatable. The ranges run 200 mΩ, 2 Ω, 20 Ω, 200 Ω, 2 kΩ, 20 kΩ and 200 kΩ; resolution starts at 10 µΩ on the 200 mΩ range and scales up with the range, and accuracy reaches ±0.02% of reading. A 4½-digit LED display refreshes 3 times per second, and the OP-232 option adds an RS232C interface for data capture and automation. 720A is NASA Range Safety approved, USAF Nonnuclear Munitions Safety Board approved and MIL-STD-810-511 compliant for explosive atmospheres, and it carries UL-913 and ISO 9001:2015 (NSN #6625-01-555-1150). Before you order, choose between the AC mains version and the battery version, and decide whether you need the RS232C port or the NSN autorange package.
Key specifications
| Number of ranges | 7 ranges: 200 mΩ / 2 Ω / 20 Ω / 200 Ω / 2 kΩ / 20 kΩ / 200 kΩ |
|---|---|
| Accuracy | ± 0.02% of reading ± 0.05% of range (200 mΩ); ± 0.02% of reading ± 0.03% of range (all other ranges) |
| Resolution | 10 µΩ (200 mΩ range) to 10 Ω (200 kΩ range) |
| Nominal test current | 100 mA (200 mΩ, 2 Ω); 10 mA (20 Ω); 1 mA (200 Ω); 100 µA (2 kΩ); 10 µA (20 kΩ); 1 µA (200 kΩ) |
| Max. test current | 100 mA |
| Open-circuit voltage | approx. 15 VDC |
| Max. input voltage | 264 VDC |
| Display | 4½-digit LED |
| Update rate | 3 readings / second |
| Connection | 4-wire Kelvin |
| Operating temperature | 0° to 50° C; temperature coefficient ± 0.002% / 1° C |
| Power | 90–240 VAC, 50–60 Hz (battery-powered version also available) |
| Dimensions / weight | 9″ × 10″ × 3″; 4 lbs (12 lbs shipping) |
| NSN | 6625-01-555-1150 |
Features
Seven ranges, wide span
7 ranges from 200 mΩ to 200 kΩ with best resolution of 10 µΩ cover winding, contact and component resistance in one instrument.
4-wire Kelvin connection
The Kelvin method takes lead and contact resistance out of the reading, so low-resistance results are accurate and repeatable.
Accuracy and stability
Accuracy to ±0.02% of reading and a temperature coefficient of only ± 0.002% / 1° C hold results steady from 0° to 50° C.
4½-digit LED display
A bright 4½-digit LED display refreshing 3 times a second is easy to read on the production line or the bench.
RS232C data interface
The OP-232 option adds an RS232C port for logging readings to a PC, automated test and data records.
Safety approvals that matter
NASA Range Safety approved, USAF Nonnuclear Munitions Safety Board approved, MIL-STD-810-511 and UL-913, made under ISO 9001:2015.
Typical applications
Winding measurement
Motor and transformer winding acceptance tests
For outgoing inspection and preventive maintenance of motors, servo motors and power transformers, engineers use the 720A 4-wire Kelvin connection to measure each phase winding precisely. Shorted turns, open windings and poor joints show up before the equipment goes into service.
Contact resistance
Connector and ground contact quality
In aerospace and defense systems a milliohm change in contact resistance is enough to distort a signal or destabilize a supply. With 7 ranges and ±0.02% of reading accuracy, test engineers screen dense connectors, ground bond points and military ordnance circuits quickly, meeting MIL-STD-810 and USAF Nonnuclear Munitions Safety Board acceptance requirements.
Component screening
Sorting and verifying precision resistors in the metrology lab
Metrology and QA labs use 720A to sort and verify precision resistors, shunts and low-value reference standards with traceability. The RS232C interface streams readings straight into an SPC system, and the battery version suits site inspections and locations without mains power.
Options and configuration
Tick the options you need. We compile the configuration into a list and carry it into the quote request form.
Power version
Hardware options
Accessory options
Downloads
Need pricing, specifications or lead time for 720A?
Also available for rent: 720A is part of the AMPTEC rental program, for project peaks, calibration backup and pre-purchase trials. Rental inquiry →