Fluke A40B Series Precision Current Shunts

  • Simplifies calibration/verification of precision calibrators and current sources
  • Shunts sized for currents from 1mA to 100A
  • Usable from dc to 100 kHz
  • 14 individual dc and ac current shunts with a 1, 2, 5 sequence over 6 decades of current
  • Simple direct measurements, making ac/dc transfers unnecessary
  • Stability typically better then ± 5.0 µΩ/Ω for one year
  • Typical angular accuracy of better than ± 0.003º at 1 kHz


The wide range of shunt values permit measuring from 0.1 mA to 100 Amps. The physical construction and the components used in the current shunts ensure that the frequency response is very flat (amplitude displacement error relative to dc resistance). Also the phase displacement at 100 kHz is small enough to be neglected in all but the highest accuracy measurements. Combined with excellent dc resistance stability, the shunts can be used to directly measure current through their full bandwidth. This simplifies precision ac current measurements as the complex ac/dc transfer measurement process will no longer be necessary for many precision current measurement applications. These characteristics make the A40B shunts ideal for traditional precision current applications such as calibrator verification. Also, the wide current range allows verification of high current transconductance amplifiers. The low phase shift error is critical for measurement of non-sinusoidal wave shapes, as found in power quality or sampling digital wattmeter measurement applications.

Technical overview

The shunts come in four different sizes. The full current shunt set includes:

  • four fully enclosed dc and ac current shunts: 1 mA, 10 mA, 20 mA, 50 mA
  • five small size radial dc and ac current shunts: 100 mA, 200 mA, 500 mA, 1 A, 2 A
  • three medium size radial dc and ac current shunts: 5A, 10 A, 20 A
  • two large size radial dc and ac current shunts: 50 A, 100 A

Voltage output is nominally 0.8 volts for the nominal rated current input. The output is measured by a voltmeter or detector, such as precision voltmeters, ac measurement standards, ac/dc transfer standards, or thermal voltage converters, fitting them to a wide variety of metrology applications.

The radial style dc and ac current shunt design gives high performance with minimum external magnetic fields. Plus, the open nature of the dc and ac current shunt physical design maximizes air flow so the shunts have a minimal power coefficient effects. This permits each shunt to be used over a wide range of currents with stable resistance characteristics.

The dc and ac current shunt resistance is designed to minimize interaction with the detector instrumentation. The 100 Amp shunt resistance is 8 milliohms, with shunt resistance increasing to 80 ohms for the 10 mA shunt. Additionally, the 1mA shunt includes an internal battery operated buffer amplifier. It drives the output voltage so the 800 ohm shunt resistance has minimal interaction with the measurement device.

Reports of calibration

The A40B series of precision dc and ac current shunts come standard with a report of traceable calibration including data. 17025A Accredited reports of calibration are available as an optional service.




Precision, low inductance shunts for dc and ac current metrology

The A40B dc and ac precision current shunt set consists of 14 low-inductance coaxial current shunts, adapters and connectors, and a rugged transit/storage case. Designed for currents from 1 mA to 100A, the current shunts are for laboratory use in making directly measured absolute ac or dc current measurements as well as ac/dc current transfer measurements. They exhibit outstanding resistance value stability, with an excellent self-heating power coefficient, and a low temperature coefficient. With all of these characteristics combined, the shunts offer direct measurement of current from dc to 100 kHz with higher accuracy than previous commercially available shunt technology. Now precision measurements can be made in a single step process rather than by more complex traditional ac/dc transfer methods.


Absolute accuracy

The following table shows the 1-year absolute accuracy specification stated at k=2, approximately 95 % confidence for the calibrated value. The specifications include 1-year stability, temperature effects over TCal ± 1 °C, and the measurement uncertainty of the calibrated value.
Shunt Nominal Current: Specification ± μA/A, TCal ±1 °C, ≤ 50 % RH 1,2,3,5
DC 1 kHz 100 kHz
1 mA 20 55 150
10 mA 20 26 26
20 mA 20 26 26
50 mA 20 23 23
100 mA 20 24 24
200 mA 20 26 26
500 mA 21 27 28
1 A 21 27 31
2 A 21 27 48
5 A 21 31 71
10 A 26 37 92
20 A 26 43 113
50 A 32 55 144
100 A 35 65 174
1 The measured current is determined from: I = (V/Rcalibrated) ×(1 + (AC-DCcalibrated /1,000,000)); where AC-DC calibrated is expressed in ppm. 2 Above 1 kHz interpolate the specification (si) between frequencies fupperand flower using: si = slower + (fi – flower) × (supper – slower) ÷ (fupper – flower) 3 Add 20 μA/A if relative humidity is outside specification limits. 4 1 mA specifications apply with the battery charger disconnected. 5 Specifications assume no loading effects due to the voltage-sensing device. See Output Voltage Measurement – Loading Effects in the operating information.

Maximum AC-DC Difference

Shunt Nominal Current: Maximum AC-DC Difference (± ppm)1,2
1 kHz 100 kHz
1 mA3 53 150
10 mA 20 40
20 mA 18 30
50 mA 13 16
100 mA 14 27
200 mA 17 28
500 mA 17 21
1 A 17 23
2 A 17 44
5 A 23 69
10 A 28 98
20 A 37 150
50 A 47 180
100 A 60 300
1 Specifications indicate the maximum flatness deviation from dc, and include both measured AC-DC difference and the uncertainty of measurement. They are stated at k=2, approximately 95 % confidence. 2 Includes 1-year stability of the AC-DC difference. 3 Specifications for the 1 mA current shunt are for TCal ± 1 °C.

General Specifications

Calibration Documentation 17025 accredited report of calibration included
Dimensions (maximum)
Shunt Value:  1 mA to 2 A
Height:  70 mm (2.75 in)
Width:  70 mm (2.75 in)
Overall Length1: 124 mm (4.9 in)
Shunt Value:  5 A to 20 A
Height:  130 mm (5 in)
Width:  130 mm (5 in)
Overall Length1: 210 mm (8.25 in))
Shunt Value:  50 A and 100 A
Height:  200 mm (7.9 in)
Width:  200 mm (7.9 in)
Overall Length1:  343 mm (13.5 in))
1 Includes input and output connectors; subject to change by component vendor.
Physical/mechanical parameters
Shunt Value:  1 mA to 20 A
Weight:  0.7 kg (1.6 lb)
Input Connector:  Type-N (female)
Output Connector:  Type-N (female)
Shunt Value:  50 A and 100 A
Weight:  3.4 kg (7.5 lb)
Input Connector:  Type-LC (female)
Output Connector:  Type-N (female)
Operating environment
Temperature: 13 °C to 33 °C
Calibration temperature (TCal) range: 18 °C to 28 °C
Humidity range for best specification 1,2: ≤ 50 % RH
Altitude: 0 m to 3,000 m
1 Resistance stability is affected by humidity, but changes are reversible. 2 If the shunts are calibrated outside this RH, stability specifications will be met as long as the shunts are stored and used at the same relative humidity ± 10 % RH.
Storage and transit environments (for models other than the 1 mA current shunt)
Temperature to avoid damage: -20 °C to 140 °C
Temperature and humidity to maintain performance1: 5 °C to 45 °C; 15 % to 80 % RH
Non-operating altitude: 0 m to 12,000 m
1 Storage at extremes of temperature or humidity will cause a temporary change of shunt resistance by up to ± 20 ppm. When subsequently stored or used within the limits of the operating environment, the shunts will recover to their original resistance value within 30 days.
Additional 1 mA current shunt specifications
Output resistance 8 mΩ
Maximum safe output current 11 mA (e.g., 1 V output into 90 Ω)
Maximum capacitive load 800 pF
Output voltage regulation 15 ppm/100 pF
Maximum output dc v offset ± 100 μV (typical ± 25 μV)
Typical error @ 1 MHz < 2 %
Battery specifications
Battery size AAA (44.5 mm x 10.5 mm)
Battery technology Nickel-Metal Hydride (NiMH)
Number of batteries required 8 (in 2 groups of 4)
Nominal battery voltage 1.2 V (4.8 V per group of 4)
Typical battery capacity 800 mAh
Storage and transit environment to preserve the batteries
Less than 90 days:  -20 °C to 40 °C
Less than one year:  -20 °C to 30 °C
Charging time (from fully discharged):  100 minutes
Maximum operating time between charges
Maximum output load (11 mA):  18 hours
High impedance load:  24 hours
Recommended cooling period:  100 minutes
  To prevent loss of battery capacity recharge at least twice per year.


Model Name


A40B/SET Complete set of shunts including:
  • 14 shunts
  • transit case
  • A40B-ADAPT/LC LC Male to LC Male adapter (1)
  • A40B-ADAPT/LCN LC Female to N Male inter-series adapter (1)
  • A40B-LEAD/4MM N to 4 MM double banana connector (2)
  • A40B-LEAD/N N Male to N Male lead (1)
A40B-001MA 1 milliamp Current Shunt
A40B-010MA 10 milliamp Current Shunt
A40B-020MA 20 milliamp Current Shunt
A40B-050MA 50 milliamp Current Shunt
A40B-100mA 100 milliamp Current Shunt
A40B-200mA 200 milliamp Current Shunt
A40B-500mA 500 milliamp Current Shunt
A40B-1A 1 amp Current Shunt
A40B-2A 2 amp Current Shunt
A40B-5A 5 amp Current Shunt
A40B-10A 10 amp Current Shunt
A40B-20A 20 amp Current Shunt
A40B-50A 50 amp Current Shunt
A40B-100A 100 amp Current Shunt

Accessories common to all models:



A40B-ADAPT/LC LC Male to LC Male adapter
A40B-ADAPT/LCN LC Female to N Male inter-series adapter
A40B-CAL/LC High current adapter to connect two shunts in series for measurement (LC to LC)
A40B-CAL/N Low current adapter to connect two shunts in series for measurement (N to N)
A40B-CASE Fiberglass Transit Case
A40B-LEAD/4MM N to 4 mm double banana connector
A40B-LEAD/N N Male to N Male lead
A40B-ADAPT/SPADE LC型插头转铲形接口适配器

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