General
PC communication
Automatic discharge

The C.A 6255 micro-ohmmeter from Chauvin Arnoux is a high-performance device for precise measurement of very small electrical resistances. It is specifically designed for applications requiring high accuracy and resolution, such as testing ground connections, contact quality in switches and relays, or evaluating cable and winding resistances. The device enables measurements in the range of approximately 1 microohm to 2500 ohms, with a maximum resolution of 0.1 microohm. This resolution is particularly important for detecting fine differences in conductivity or the condition of metallic connections.

Applications

The C.A 6255 is used in industrial electrical engineering, machine building, and the maintenance of electrical installations. It is used to check ground continuity quality, metallization, and surface condition of components, as well as to evaluate contact quality in switches, relays, and other electrical contacts. Measuring cable and winding resistances, for example in motors and transformers, is also possible. The ability to detect winding heating makes the device suitable for diagnosing overloads or defects in electrical machines.

Functions and Equipment in Detail

The device offers three measurement modes: inductive, ohmic, and ohmic with automatic triggering. The inductive measurement mode is particularly suitable for test objects with high inductance, as it enables optimized current generation. The four-wire measurement ensures that lead and connection resistances do not affect the measurement, thereby increasing accuracy. Automatic compensation of interference voltages at the terminals minimizes measurement errors caused by external influences. Additionally, automatic discharge is performed after measurement to ensure no residual voltage remains on the test object.

Technology Explained Simply

Measurements are performed using test currents up to 10 amperes, with three of the seven measurement ranges supporting this maximum current. The high resolution of 0.1 microohm enables detection of minimal resistance changes, which is important for diagnosing wear or corrosion. Temperature compensation is achieved using a Pt100 temperature sensor, which converts resistance values to a reference temperature. This is particularly relevant because electrical resistance of materials is temperature-dependent. Storage of up to 1500 measurement values allows for later evaluation, with data transferable via PC communication.

Compatibility and Accessories

To extend the range of applications, retractable Kelvin test probes for 10 A are available as accessories. These enable safe and precise contact with test objects, especially at high currents. The test probes are designed for easy handling and support accurate measurement at tight or hard-to-reach locations.

Mounting and Installation

The device is designed as a portable measuring instrument and requires no special mounting. It is directly connected to the test object, with the four-wire method ensuring the measurement is not influenced by lead or connection resistances. Power supply is via a rechargeable NiMH battery, enabling mobile use. Dimensions are 270 x 250 x 180 mm, and weight is 4 kg.

Operational Advantages

The combination of high resolution, four-wire measurement, and programmable alarms enables reliable and reproducible measurements. Automatic discharge after measurement increases safety, and PC communication simplifies documentation and evaluation of measurement results. The safety class 50 V CAT III ensures operation in industrial environments with increased electrical loads.