Winding resistance meters ATRM-20/ATRM-40

Winding resistance meters ATRM-20/ATRM-40

The ATRM-20 and ATRM-40 are Amperis’ third generation transformer winding resistance meters. The ATRM line is designed specifically to measure DC resistance values of transformer windings, rotating machine windings, or any dc resistance of an inductive device. The ATRM line features dual resistance-reading input channels that can measure two winding resistances simultaneously (primary and secondary windings of a transformer).

Both the ATRM-20 and ATRM-40 can provide a fast and stable reading of very large transformers by utilizing a 60Vdc power supply. The ATRM-20 is capable of outputting a selectable test current from 1A to 20A while the ATRM-40’s test current is selectable from 1A to 40A.


  • Computer Interface

The ATRM can be connected to a PC via the unit’s RS-232C, USB, or Bluetooth interface. The included Windows®-based Transformer Winding Resistance Analyzer (TWRA) software can be used to retrieve test records (stored in the ATRM or on a USB Flash drive) or to run tests from the PC. Test records are automatically
exported to PDF, Excel, and XML formats.

  • User Interface

The ATRM features a back-lit graphic LCD screen (128 x 64 pixels) that is clearly viewable in both bright sunlight and low-light levels. An alphanumeric keypad is used to enter test information and to operate the unit.

  • Safety Features

The ATRM automatically dissipates the energy stored in the transformer at the end of each test The discharge circuit will continue to work even if the ATRM power supply is lost.

  • Test Record Storage

The ATRM can store up to 256 static test records (111 readings per record) and 120 dynamic test records internally. For external test record storage, the ATRM features a USB Flash drive interface port. Up to 999 test records can be stored on a connected USB Flash drive.

ATRM-20/40 Technical specifications


Portable transformer winding resistance meter

Physical specifications

21”W x 17”H x 9” D (53 cm x 43 cm x 24 cm); Weight: 33 lbs (15.4 kg)

Operating voltage

100 - 240 Vac, 50/60 Hz

Resistance reading range

ATRM-20: 1 micro-ohm - 2000 ohms; ATRM-40: 1 micro-ohm - 500 ohms


1 - 19,999 micro-ohms: ±0.5% reading, ±1 count;

20 - 999 milli-ohms: ±1% reading, ±1 count;

1- 2000 ohms: ±1.5% reading, ±1 count

Test current

ATRM-20: 1A ¬ 20A in 1A increments; ATRM-40: 1A ¬ 40A in 1A increments

Test voltage

60Vdc charging, 18V DC max during measurement

Resistance channels

Two static resistance reading channels


Back-lit LCD screen (128 x 64 pixels); viewable in bright sunlight and low light conditions


Built-in 2.5-inch wide thermal printer

Internal data storage

256 static test records (each can contain up to 111 readings) and 120 dynamic test records

External data storage

Up to 999 test records on external USB Flash drive

Computer interface

RS-232C, USB, and Bluetooth


Designed to meet UL 61010A-1 and CAN/CSA C22.2 No. 1010.1-92 standards


Operating: -10°C to +50°C (+15°F to +122°F); Storage: -30°C to +70°C (-22°F to +158°F)


90% RH @ 40°C (104°F) non-condensing


2,000 m (6,562 ft) to full safety specifications


One 50-foot current cable set, two 50-foot resistance sense cable set, one LTC control cable, one ground cable, one power cord, One RS-232C cable, one USB cable

Optional accessories

Transportation case


1 year on parts and labor

NOTE: the above specifications are valid at nominal voltage and ambient temperature of +25°C (+77°F). Specifications are subject to change without notice

Controls scheme winding resistance meters ATRM-20/ATRM-40Connections winding resistance meters ATRM-20/ATRM-40Test results winding resistance meters ATRM-20/ATRM-40

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