GMW Hall-Effect AC/DC Probes: Overview and Performance Review

GMW brandFounded in 1982 in Redwood City, California, established a factory in San Carlos in 1991, and for many years focused on sensors,

and the research and production of test and measurement instruments.

GMW's CPC/CPCO series clamp-type (open) Hall-effect current sensors can measure AC/DC current from 0 to 16000 A over a DC–75 kHz (Max) bandwidth,

Overall measurement accuracy is 1%, and it is mainly used for current testing of electric vehicles, motors, PV inverters, variable-frequency drives, battery charge/discharge, electromagnetic actuators, etc.

It can usually be used with various power analyzers, recorders, data loggers, and oscilloscopes for testing.

I. GMW Hall-effect current probe product introduction

1. Basic principle

The measurement principle of the GMW probe uses an array of magnetic sensors to detect magnetic field strength and then performs integration to calculate the magnitude of the current flowing through.

2. Product dimensions

GMW Hall-effect current probes are divided into 3 series by aperture size. The CPC series has a clamp-type 27 mm aperture, spring-controlled automatic closing, and is easy to use,

CPCO has 77 mm and 160 mmtwo large apertures, which require a flathead screwdriver to manually open and lock. The open-loop design with a large aperture is suitable for more test scenarios.

3. Current ranges

The 3 series of GMW Hall-effect current probes have different current ranges and bandwidth frequencies.

CPC series range 250 A–2000 A, DC bandwidth ~75 kHz;

CPCO-77 aperture series range 500 A–12000 A, DC bandwidth ~40 kHz;

CPCO-160 aperture series range 1000 A–16000 A, DC bandwidth ~50 kHz

The full series can measure AC/DC currents from 0 to 16000A; the main advantage is high current. For example, 1%-accuracy Hall probes from the mainstream brands we commonly see generally

can measure DC only up to 500A (750Apk); GMW Hall probes effectively fill the gap in the high-current field.

II. Main features of GMW Hall-effect current probes

• Open-loop design with very high adaptability to application scenarios;

• No internal magnetic core; no need to worry about overcurrent magnetic saturation;

• Extremely large measurement range, up to 16000A;

• Three aperture sizes (large, medium, and small) to suit various measurement environments;

• AC/DC operation;

• High compatibility; the output can be connected to instruments such as oscilloscopes and power analyzers;

• Compact design; the unit is lightweight and easy to carry;

• 1% high accuracy (also the topic of this installment)

  
  

III. Typical applications

• Vehicle test bench

• In-vehicle testing

• Current measurement for variable-speed motor drives

• Charging and discharging current measurement for new-energy and energy-storage batteries

• DC/AC current measurement and control for photovoltaic inverters

• Current measurement during operation in rail transit (fully sealed)

  
  

The CPC series is small and can be installed in many difficult locations, such as the motor gap shown in the figure

As shown in the figure, three GMW CPCO current probes, with a range of 16000A and an aperture diameter of 160 mm, are installed between the circuit breaker and the cable to the track

Current measurement is performed on the branch busbar of the electric train.

Above, we have gained a brief systematic understanding of GMW Hall-effect current probes; below, we evaluate the accuracy of two probes from different series,

to verify whether they can achieve the 1% accuracy specified by the manufacturer.

IV. Evaluation equipment and evaluation principle

The auxiliary equipment for this evaluation mainly includes a Fluke 5500A standard source and a power supply and signal processing unit (self-made by 探头之家),

Output display uses a Fluke 8845A 6½-digit high-precision digital multimeter.

Because the maximum output current of this standard source is only 11 A, while our current probe samples are 1000 A and 2000 A,

so in the evaluation experiment we added a 50/100-turn coil device to amplify the current,

so that the measured current reaches a relatively reasonable point within the probe's measurement range (the current is still not large enough after multiplication).

Additionally, regarding the power supply, it should be noted that we did not use the manufacturer-provided one-input/two-output cable and power supply (the manufacturer's power supply is also not self-produced),

because our self-made cable has better connectors and more stable transmission, and the power supply and signal processing unit are more convenient to use.

Evaluation principle: the standard source outputs current — the current is amplified several times by the coil — measured by the probe — output to the multimeter for display.

Here, the probe has an mV/A transfer ratio that attenuates and converts the large current into a small voltage signal.

V. Performance evaluation (see the video below in this issue for details)

1、CPCO-2000-77-BP10 DC accuracy evaluation

The standard source provides DC currents of 1 A/5 A/10 A; after the current is amplified 100 times by the coil,

it is measured by the probe and output to the multimeter; the table below shows the results of three DC measurements:

After conversion to voltage based on the probe transfer ratio, the errors compared with the standard theoretical values are all within the specified 1% accuracy range; this measured current signal

is still in the relatively small range of the probe's measurement range; there is no way around it, as the equipment capability is limited. From the results, we can see that the error at 100 A is relatively large, because 100 A

is within 5% of the probe's 2000 A range; in practical applications, we do not recommend measuring in this way. Selecting an appropriate range has a smaller effect on the error.

2、AC accuracy evaluation of model CPCO-2000-77-BP10

The standard source provides AC currents of different magnitudes and frequencies; the current is amplified 100 times by the coil and then measured with the probe and output to the multimeter,

The following table shows the results of 5 AC measurements:

The AC evaluation results are relatively stable; due to limited equipment capability, high-frequency large currents cannot be driven. This time, the performance at 100 A and different frequencies

is slightly better than DC, and the overall measured results are all within the specified accuracy range.

3. DC and AC accuracy evaluation of model CPC-1000-27-BP2

This model has a slightly smaller aperture; the 100-turn coil cannot clamp on, so it can only be changed to 50 turns. The current output by the standard source is amplified 50 times, and the probe ratio is 2mV/A,

DC currents of different magnitudes and AC currents of different frequencies were measured; the measured results are as follows:

The evaluated current is 10% to 50% of the probe range,Overall accuracy performance is good.

For this model, we used the original manufacturer's one-input two-output cable; no separate power supply is required, and it is powered directly from mains via USB, which is very convenient.

The above is a real evaluation we conducted on these 2 probe samples,

The detailed video can beviewed by logging in to [探头之家]WeChat Channelsto watch the collection.

6. About Accuracy

The evaluation results in this issue only represent the environment and test conditions of the 探头之家 Power Electronics Center Evaluation Laboratory and are for reference only.

In addition to factors such as range and equipment performance, it is particularly noted that engineers always encounter many complex measurement environments in actual operating conditions, and different measurement environments will also greatly affect probe accuracy.

High-temperature environment

During measurement, each probe has an operating temperature range. Measurement within the operating temperature range ensures accuracy; as the limits of the operating range are approached, accuracy will inevitably decrease.

High magnetic field environment

In complex circuits, strong magnetic interference may cause signal distortion and severely affect accuracy; measures such as shielding are required.

Outdoor environment

Extreme factors such as rain, direct sunlight, and lightning strikes will affect the probe's real-time measurement to a certain extent, and changing environmental conditions will also affect its accuracy.

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