Programmable Micro-Ohmmeter

Model 4300C

4300C Programmable Micro-Ohmmeter
4300C Programmable Micro-Ohmmeter Back View
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  • User Selectable Test Current Up to 10 Amps.
  • Boosted Compliance Voltage Mode for Rapid Charging of Motors and Transformers.
  • Safety Disconnect Status L.E.D.s.
  • Test Current On/Off Switch.
  • Selectable Voltage Sensitivity:1μV-10μV-100μV
  • 18 Combinations of Voltage Sense/Current provide optimum measurement conditions
  • Selectable Display Rate (100ms-to-500ms)
  • VFD Display w/Adjustable Intensity
  • RS-232 Serial Interface
  • Programmable Temperature Compensation
  • Built-In Limit Comparator w/Visual-Acoustic Indications and Rear Panel Relay Terminals
  • Run/Hold w/Peak Detector
  • Print/Log Function


  • USB Interface
  • IEEE Interface
  • BCD Interface
  • JB-2 (Rear Locking Connectors)


  • OmniCompensator (Temperature Sensor)
  • RS (Remote Foot Switch)
  • 19″ Rack Mount Adaptor

Test Leads:

  • K – Kelvin Lead Set (Alligator Clips)
  • KK – Heavy – Duty Lead Set (Alligator Clips)
  • KC – Heavy Duty Lead Set for JB-2
  • C – Banana-Clip Cable
  • MP-1 – Kelvin Micro-Probes (Needle)
  • MP-2 – Kelvin Mini-Probes (Needle)
  • MP-S – Single Pointed Probes (Needle)
  • MP-4 – 1″dia Surface Probes
  • MP-5 – 0.5″dia Surface Probes
  • BBL – Banana-to-Banana Cables
  • SL-48 – Low termal Leads (Lugs)

Performance That Conquers Any Resistance

The 4300C Digital Micro-Ohmmeter measures a variety of low-resistance devices ranging in value from 100nΩ to 20kΩ. The flexible measurement format of the 4300C provides six ranges of user selectable test current (from .1mA to 10A) and three voltage sensitivity settings (20mV, 200mV and 2V). The unit’s 4½ digit resistance readings are displayed on a high contrast LCD display and are optionally available via optional BCD, RS-232 or GPIB interface.

Features of the 4300C include: four terminal compensation, a very low 2mΩ range, selectable test current levels (up to 10 amps), a fast settling charge inductor mode, safety disconnect status indicators, automatic temperature compensation, a basic accuracy of ±0.03% and a push button or GPIB controlled current on/off selector.

Transformers, Motors, Cables, and More:

The 4300C is the perfect instrument for tackling ultra-low resistance testing requirements associated with motors, transformers, fuses, connectors, breakers, bonding/weld resistance and many other applications. For rapid testing of inductive loads the 4300C’s charge inductor mode provides in excess of 20V compliance. This model reduces settling time by a factor of 5:1 on inductive loads. The result is valid readings in minutes instead of hours when testing 400MW utility transformers. A solid-state “Crowbar” design provides front end protection for up to 500 amps of induced current.

Charging Inductor Mode Indicator:

The Valhalla 4300C charging inductor mode LED, indicates when the unit’s current source compliance voltage is exceeded. The 4300C “Boost Mode” then increases the compliance voltage to exceed 20V output to reduce the settling time (charges the inductance) when inductive loads (i.e. large transformers) are being measured.

Disconnect Status Indicator:

The Valhalla 4300C safe and unsafe LED’s indicate when it is safe to disconnect the test leads from the load. When a highly inductive load is being measured, a potentially lethal back-EMF (collapsing field) is induced when the test current is removed. The Valhalla 4300C internally automatically provides a discharge path for this back-EMF and monitors voltage. The safe to disconnect LED is illuminated when the back-EMF is less than 5V. The 4300C test current can be turned off and on via the test current switch or GPIB command.

In addition, the LED above the test current switch indicates the current source status. The 4300C’s variable test current levels are selected via a six position rotary switch of GPIB command. The test current and full scale voltage sensitivity switch positions determine the resistance range as indicated by the front panel matrix.

Large Inductor Resistance Measurement: The 4300C’s 10A current source is ideal for low resistance inductors such as utility transformers. Combining the current output with boosted compliance voltage (>20 VDC) enables rapid stable resistance readings in seconds, not hours. Having unique features like Automatic Temperature Compensation, High Level Current Sourcing (10A) with High Compliance Drive circuitry and 18 combinations of Voltage / Current Range Selectivity, the 4300C Digital Micro-ohmmeter is second to none.

Automatic Temperature Compensation:

Copper and aluminum will exhibit approximately a 0.4% change in resistance for a 1°C change in ambient temperature. When in Automatic Temperature Compensation mode (TCM), the Valhalla 4300C temperature sensor automatically senses the ambient temperature and references the resistance value of the test item equivalent to being in a 20° C controlled environment. A 10° C change in ambient (i.e. open air, shop floor) provides a 4% change in the resistance of a copper item. Without this “TCM” feature, a micro-ohmmeter which may be 0.02% accurate may be making a 5-10% resistance measurement error when measuring copper or aluminum (i.e., transformer wire) material.

Virtually all competitive micro-ohmmeters lack copper or aluminum (TCM) ambient temperature coefficient of resistivity compensation. Ambient temperature can have drastic effect on the resistivity of a conductor. Without temperature compensation, materials can easily be erroneously classified during the resistance testing process. Correcting the resistance measurement on copper conductors, while ambient temperature varies makes “TCM” a very useful feature.

Other Features

The Model 4300C can also be programmed for Hi-Lo limit comparison. Three front panel LEDs allow a visual of the result and a rear panel relay closure screw terminal block can be used to implement an automated batch sorting system for components or products, operate counters, sound alarms or shut off a process. A Run/Hold function is also a standard feature of the 4300C. The user can program this function as a peak hi or peak low detector. Measurements may be printed or logged and viewed in a spread sheet by using the Print/Log feature also standard with the Model 4300C.