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10 A Digital micro-ohmmeter MPK256

Q: What is a micro-ohmmeter?

A micro-ohmmeter is a measuring instrument for very low resistances (from a few nanohm to milliohm). It uses a 4-wire (Kelvin) measurement method to measure cable and contact transitions without measurement error of measurement leads.u003c/pu003e

Q: How does the 4-wire (Kelvin) method work?

Two lines send a known current (I) through the object, two separate lines measure the voltage drop (V) directly across the object. The resistance is R = V/I. Since no measuring current flows through the voltage lines, cable and terminal resistances do not affect the measurement.

Q: What do you use a micro-ohmmeter for?

Contact resistance of switch/disconnector contacts and busbars Weld and bolt connections, bus bars, earth connections Transformer windings (fast DC resistor, not for extended WRT) Motors: winding and connections, rotor/stator transitions Quality control of cables and feedthroughs

Q: Which measurement ranges and resolutions are common?

Resolution: 0.1 μΩ to 1 μΩ. Ranges: from ~0.1 μΩ to u0026gt;200 mΩ (sometimes up to a few ohms). For each model, check the combination of resolution, accuracy and maximum test current.

Q: Why is test current important?

Higher test current gives a larger voltage drop and thus a better signal-to-noise ratio-essential for very low resistors. For contact resistors in high-current applications, 100-200 A is common; for general connections, 10-20 A is often sufficient.

Q: Is more testcurrent always better?

No. Too high a current can generate heat and temporarily increase the resistance (self-heating). Choose a current that suits the application and follow the duty-cycle of the instrument.

Q: What does ‘accuracy’ mean in micro-ohmmeters?

Usually specified as ±(percentage of readout + number of digits). Note that for low absolute values, the “digits” component weighs relatively heavily. Also check noise filtering and repeatability.

Q: What is temperature correction?

Copper and other metals have a temperature coefficient (Cu ~0.00393/°C). For comparisons over time, correct to a reference temperature (usually 20°C). Some instruments do this automatically with an internal/external temperature sensor.

Q: Can I measure inductive loads (motor/trafo)?

Yes, but note that the current builds up more slowly and energy can be stored. Use instruments with suitable protection/discharge function. Wait for “discharge complete” before disconnecting.

Q: What are common measurement errors?

Measuring 2-wire instead of 4-wire Clamps too far apart/no fixed position Dirt/oxidation between clamp and conductor Insufficient discharge of inductive objects Not waiting for thermal equilibrium or stabilisation

The MPK256 is a portable, battery-powered micro-ohmmeter for test currents from 1 mA to 10 A. With a resolution of 1 µΩ and a measurement range up to 2,000 Ω, this is the versatile instrument for resistance measurements on switches, transformer windings, motors, cables and busbar connections.

Compact (6.5 kg), IP65 enclosure, built-in printer, 30,000 readings memory and rechargeable LFP battery. Including MegaLogg 3 software and 2-year factory warranty.

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MPK256 — the versatile micro-ohmmeter up to 10 A

The MPK256 is a portable, microprocessor-controlled instrument for accurately measuring very low resistances. With 6 selectable test currents from 1 mA to 10 A — each continuously adjustable from 0 to 100% — and a measurement range from 1 µΩ to 2,000 Ω, the MPK256 covers a wide range of applications.

The 4-wire (Kelvin) measurement principle eliminates errors caused by test lead and contact resistances. The open circuit output voltage of up to 10 V reduces stabilisation time when measuring highly inductive elements. The measurement circuit is protected against voltage spikes from inductive objects.

Operation is simple: connect the test leads, select the test current and press start. After a few seconds, the reading appears directly on the display with unit indication (Ω, mΩ or µΩ). The rugged IP65 case (6.5 kg) makes the instrument suitable for both laboratory and field work.

Applications

Switches and circuit breakers — contact resistance measurement on switch contacts, disconnectors and relays
Transformers — DC resistance measurement of windings to detect poor connections and winding faults
Motors and generators — resistance measurement of rotor and stator windings, phase symmetry
Busbar connections — verification of bolted and welded joints for transition resistance
Cables and conductors — resistance measurement of cable samples, cable lugs and connectors
Grounding systems — measurement of earth connections and bonding
Quality control — incoming inspection of components and semi-finished products

Key features

6 test currents — 1 mA, 10 mA, 100 mA, 1 A, 5 A and 10 A, each continuously adjustable (0–100%)
Resolution 1 µΩ — at 10 A test current
Measurement range up to 2,000 Ω — at 1 mA test current
Accuracy ± 0.2% — of reading ± 2 digits
4-wire (Kelvin) measurement — elimination of test lead and contact resistances
Output voltage up to 10 V — reduced stabilisation time for inductive loads
Built-in thermal printer — direct printout of measurement results
30,000 readings memory — transferable via USB
IP65 enclosure — dust and waterproof with closed lid, 6.5 kg
Rechargeable LFP battery — 12 V, 6,000 mAh, or mains supply 100–240 V
Protected against inductive spikes — safe measurement on motors and transformers
Bluetooth and USB — for remote control via Android app and data transfer
2-year warranty — standard Megabras factory warranty

MegaLogg 3 software

The MPK256 is supplied with MegaLogg 3 desktop software for transferring, analysing and reporting measurement data via USB. The instrument also supports wireless control via the BlueLogg Android app — including remote control, GPS location and photos of test objects.

When to choose the MPK256, MPK105R or MPK215R?

The MPK256 is the versatile base model: 6 test currents up to 10 A, wide measurement range up to 2,000 Ω, ideal for general resistance measurements on switches, windings and cables. For higher test currents up to 100 A with BSG mode and IP65 for substations, the MPK105R is the choice. For maximum test current up to 200 A in heavy industrial applications, see the MPK215R.

Answer your questions on micro-ohm measurements

What is a micro-ohmmeter?

How does the 4-wire (Kelvin) method work?

What do you use a micro-ohmmeter for?

Which measurement ranges and resolutions are common?

Why is test current important?

Is more testcurrent always better?

What does ‘accuracy’ mean in micro-ohmmeters?

What is temperature correction?

Can I measure inductive loads (motor/trafo)?

What are common measurement errors?

How do you interpret contact resistance?

How does a micro-ohmmeter compare to a winding-resistance tester?

Gijsbert from IONIO will be happy to help.

At IONIO, we not only supply advanced testing and measurement systems, but also offer clear and expert advice to optimise the testing of your product. Find out how we can improve your business processes. A consultation can be scheduled in no time!

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