Clamp-on DC Meters

One-of-a-kind Clamp-on DC Ammeters

The Swain Meter™ Company manufactures portable clamp on DC ammeters that precisely measure the magnitude and direction of DC current flow on any conductor. Used both onshore and offshore, Swain DC clamp on amp meters accurately read current from 5mA to 200 Amps with a resolution of 1mA in the 0-2Amp range.

Swain MER™ and Auto MER™ meters cancel out AC interference up to 10Amps to establish a +/- 1% reliability specification. MER™ is “Magnetic Error Reduction”, a patented technology (US patent 6,323,635 1) is constructed to cancel out the earth’s magnetic field and establish an error-free baseline from which precise readings are obtained.

Two models of Swain are manufactured: the Auto MER™ and soon to be released Auto MER™ GEN 3.0  meters. Both offer fast, precision accuracy to read magnitude and direction of current. The Auto MER™ GEN 3.0 meter will be capable of AC and DC amperage measurements. This new meter will also have built in measurement data storage capable of being downloaded via USB. A rechargeable battery has been incorporated into the Auto MER™ GEN 3.0 meter as well.

MER™ Meter

The MER™ meter has been discontinued as of January of 2018.


  • Optional external battery operation.
  • Measures direct current without interrupting the circuit.
  • Magnetic Error Reduction (MER™) type Clamp DC Ammeters™ are generally more accurate for measuring direct current with a non-contact sensor. They are constructed to substantially reduce zero offset error due to non-uniform magnetic fields common on steel pipe, near rebar, or near the battery in cars and trucks. The benefit is usually two or three to one over comparable standard Swain Meters.
  • Offshore platform anode current or transmission line current can be measured at 700 ft. depth or more. MER™ DC Clips (to 8″ dia.) and Clamps (to 100″+ dia.) work undersea for a long time when waterproof connectors are provided. The origin of these sensors were called Sea Clip™.
  • Accuracy is ±1% reading, ±3 digits. User friendly 31/2-digit LCD meter with polarity and 1/2″-high numerals.
  • Protected from 300 A overload.
  • AC input current is rejected to less than 5 mA change with 10 A input.
  • Portable, with auto off, or full on for recorder, 50 hr. typical alkaline internal battery life. Test Battery range provided.
  • 3/4″ Clips to 100″+ dia. Clamps, which work in a desert, or 700 ft. under water with optional waterproof connectors and extensions.

Auto MER™ Meter

The Swain Auto MER™ DC Current Clamp Meter is a test meter for corrosion detection that features auto ranging and auto zeroing. MER™ stands for Magnetic Error Reduction.

Our Pelican brand case design is water resistant and uses dust proof, military style, Cannon Connectors. Data logging output jacks are a standard item on all Auto MER™ and MER™ Meters.


  • Optional external power source available.
  • Measurement range is selected automatically — typically 2, 20, or 200 A., within seconds of a change of input current. Zero is also automatically and precisely set.
  • Auto MER™ model DC Amp Current Clips are generally more accurate. They are constructed to substantially reduce zero offset error due to residual magnetism in transmission line pipe, or magnets in vehicles. The benefit is usually two or three to one over comparable standard Swain Meters.
  • Polarity (direction of flow) of measured current is shown both on the LCD meter and also at the output terminals.
  • Auto MER™ is fully portable, with 50 hr. battery and “Low Batt” icon.
  • In “Auto”, Range selection, Zero adjustment, and also battery OFF are automatic.
  • In “Manual”, Range is selected and Zero is set by hand. Battery power stays on.
  • External Battery is optional.
  • Resolution: 0-2Amp range is 1mA, Zero to 20Amp range is 20mA, Zero to 200Amp range is 100mA MAX resolution.
  • Clamps with 24″ to 60″ inside diameter have 10 mA max. resolution.
  • Accuracy is ±1% reading, ±3 digits, ± zero offset due to magnetism. The LCD meter has 3½ digits with ½” high numerals.
  • Output for a recorder is ±2 V at full scale input on any range. Overrange is available. AC input current is rejected to less than 5 mA change with 10 A rms – 60 Hz input.

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