Shaft Voltage Detection Device

Helwig Carbon’s Patented Shaft Voltage Detection Device otherwise known as the BPK-Probe™ is an instrument designed to measure common mode voltage on a motor shaft and determine the risk of discharge through the motor bearings. It also has the capability to switch in Helwig’s Bearing Protection solution. This feature allows the user to measure the performance of our grounding device and the risk of further damage to the motor bearings once installed.

The BPK-Probe™ comes as part of a complete kit including everything you need to test motor shafts or other devices where damaging discharges may be present. A tablet oscilloscope is included for more detailed analysis of shaft voltages, but is not required to conduct testing.

PATENT 10942203

BPK Probe with parts of the probe pointed out
kit image
kit image close up
  • BPK-Probe™
  • Probe Preparation Tool
  • Probe Extension Tube
  • 2-replacement brushes
  • Micro-USB charge cable
  • Tablet Oscilloscope
  • Oscilloscope charge cable
  • BNC cable
  • SD Card Adapter
  • USB stick
Made in USA logo, showing that our kits are crafted in the USA, static grounding bearing for brushes

BPK-Probe™ FAQs

A patented instrument used to measure, record, and display voltage on a motor shaft that, when discharged through the motor bearings, damages and reduces the life of the bearing. In addition, it also has an embedded grounding device to show the effectiveness of Helwig’s Bearing Protection Kit™ (BPK).

The BPK-Probe™ uses (2) propriety silver graphite brushes to directly contact the motor shaft. One brush is used to measure shaft voltage, the other is used to ground the shaft. The measured voltage is displayed on the Probe’s LCD screen.

There are two versions of the BPK-Probe, the older version, V1, and the new version, V2.  The V2 probe was developed with new and upgraded features including the ability to connect to Helwig’s newest product, the BPK-Probe DataLink app.  The two versions are easily distinguished by the display screen. The main differences are the color of the display and the status icons. Also, only the V2 versions are eligible for a firmware upgrade to enable the probe to link to the DataLink App.  Follow the simple steps below to be able to tell the version of your probe and if a firmware upgrade is already installed or has the ability to be installed.

Version 1 has a monochrome (non-color) display and is not eligible for the firmware update.  Therefore, it is not able to connect to the DataLink app.

Version 2 has a color display with added features and status icons.

  • If you see the 2-digit alphanumeric code in the upper right corner, your probe is upgraded with the latest firmware and able to connect to the DataLink app.
  • If you see a color display but no 2-digit number, the probe still needs the firmware upgrade to be able to connect to the DataLink app.

Motors driven from a Pulse Width Modulation (PWM) source or  Variable Frequency Drives (VFD) are common sources of unwanted shaft voltage due to the common mode voltage they create. Typically, whenever a speed control is used there is risk of voltage building on the motor shaft causing bearing discharges. Please Note, there are other sources of bearing discharges to consider such as asymmetry in large frame DC motors. Please contact Helwig Carbon if you feel your motors are at risk.

Bearings suspected of damage due to electrical discharge should be removed, cut and examined for ball bearing frosting and raceway fluting. A qualified repair shop or Helwig Carbon can assist with this analysis.

Yes. Driven devices like drive shafts, drums, propeller shafts, gearboxes, or etc… are all susceptible to damaging discharges due to common mode or static voltage discharge and should be monitored.

With the BPK-Probe™ grounded, typically to the motor frame, the Probe tip is placed against the rotating motor shaft and the test is performed. The Probe’s display indicates a Pass/Fail status along with the measured voltage level. See the BPK-Probe™ Operating Guide for additional information on safe and proper use. Factory training is recommended, please contact Helwig Carbon for more information.

Once safe access to the motor shaft is established the test only takes seconds. The risk to the motor is immediately displayed and recorded following each test for real-time, on-site, evaluation.

The Probe is factory tested and calibrated to be accurate. In addition, the Probe includes a BNC output. This output can be connected directly to the tablet oscilloscope or other 3rd party device to verify the test results. Reference the BPK-Probe™ Operating Guide and Tablet Oscilloscope Operating Guide for details.

The ground cable and clamp included with the BPK-Probe™ kit is designed to provide a solid uninterrupted ground path. With the ground contact surface clear of debris and paint, the ground clamp and cable will properly ground the probe. If you suspect an inadequate ground connection, please change the ground reference point and take additional readings. Contact Helwig Carbon with questions.

Although the ground cable and clamp are securely connected to a ground source the ground itself may be corrupt. A quick test with the BPK-Probe™ with the Ground Switch Enabled will check the ground source. If a corrupt ground is detected a GROUND ERROR will be displayed on the Probe’s display. Please contact Helwig Engineering for more information.

No. A Digital Voltmeter (DVM) cannot be used to measure bearing discharge potential. The method and sample rate used by DVMs prevent them from properly measuring discharge potential.

Helwig includes (2) replacement brushes with each BPK-Probe™ Kit. Replacement tips and brushes are available and stocked at Helwig Carbon.

Yes. In addition, the BPK-Probe™ Handle and all accessories are available for replacement if lost or damaged.

Yes, but it must be a 100Mhz or faster scope. Please Note: High Quality Tablet Oscilloscopes are an optional add-on to the standard BPK-ProbeTM kit. Please contact Helwig for details.

Yes, each test is recorded on the micro-SD card inserted into the BPK-Probe™ Test data can be downloaded to your PC through the Micro USB port on the Probe handle. You can also use the Probe’s BNC output to capture detailed test results on the included tablet oscilloscope or other 3rd party devices.

Yes, it is rechargeable through the micro-USB port on the handle. Battery and charging status is indicated on the display.

The BPK-Probe™ does have wireless Bluetooth capabilities and will soon be fully functional with a mobile app.

Helwig offers an optional “Remote Box” option allowing test/verification and performance testing of an installed BPK. The Remote Box allows the motor shaft to be tested using the BPK-Probe™ without contacting the motor shaft with the probe. This provides a convenient way for test and performance verification at any time without guard removal, scheduled downtime, etc. Please contact Helwig Engineering for more information.

Helwig does not recommend using the BPK-Probe™ or any other instrument in explosion-proof or otherwise hazardous environments. Follow all safety precautions and regulations when using the BPK-Probe™. For more information please contact Helwig Carbon.

Yes, in most cases there is access to the motors Opposite Drive End (ODE) or to the line shaft or gear box the motor is driving. Contact Helwig Carbon for more information.

Yes. Helwig has qualified factory-trained local REPs that can perform tests at your location. In addition, Helwig offers an Engineering Service for a more detailed engineering analysis of the application. Contact Helwig Carbon for more information or to schedule a visit.

The BPK-Probe™ will display simple-to-read Pass/Fail test results based on industry standards for bearing damage. For a more detailed analysis, Helwig recommends recording the test results on the optional tablet oscilloscope and forwarding those results to Helwig Engineering for analysis.

Yes. Cleaning the tip with a stiff wire brush should remove embedded debris. Replacement stones are available.

Yes. The optional tablet oscilloscope is delivered with pre-set factory defaults to optimize performance when used with the BPK-Probe™. If the settings are changed there is a simple step-by-step procedure to reset the factory recommended defaults. Please consult the Tablet Oscilloscope Operating manual or contact Helwig Carbon for details.

Yes. The kit includes operating instructions for both the BPK-Probe™ and the oscilloscope when included. In addition to the step-by-step instructions covering all the basic information, you need to test, and record data Helwig Carbon also offers Factory Training. Factory Training includes an in-depth review of shaft discharges, their cause, and effect, grounding, proper use of the Probe. It also covers how to measure, capture and interpret data. To become Factory Certified please contact Helwig Carbon to make an appointment.

No. The BPK-Probe Grounding Error feature is designed to check the quality of the ground source the Probe’s ground clip is connected to when testing motor shafts. The BPK-Probe is not designed to isolate, track down or correct grounding issues at your facility. If you receive a Grounding Error test result when testing the motor shaft for bearing discharges please consult a qualified electrician before proceeding.

Probe Trigger & Patent
Probe Tips
brushed images
BNC Output
Probe Tool 2.0
Probe tool example

BPK-Probe™ Shaft Voltage Detection Device Operating Guide


Tablet Oscilloscope Operating Guide

BPK-Probe™ Basics 101

BPK-Probe™ Blog Posts

BPK Probe on a stand

From Probe to Patent

Helwig Carbon Products, Inc. is proud to announce that the BPK-Probe™ has been issued US Patent #10942203.  This major innovation provides a means to detect induced shaft currents in motors controlled by VFD drives.

silver graphite powder

K007: Exclusive Silver Graphite Brush Grade

Helwig Carbon provides the shaft grounding industry the lowest resistant path to ground via a proprietary silver graphite brush grade to protect from damaging VFD-induced shaft currents.  This one-of-a-kind brush grade is 5X lower in resistance than

test for shaft voltage

Testing Shaft Voltages for Bearing Current Protection

Motor bearings are essential components in electric motors that provide support and facilitate smooth rotation of the motor’s rotating shaft. However, as electrical currents flow through motor bearings this can cause damage and shorten your motor’s lifespan.

BPK Probe ROI Blog, the BPK-Probe™ is an easy to use instrument specifically designed to measure the risk for damage to motor bearings, gearboxes, or other devices.

Achieving an ROI with the BPK-Probe™

Problem Overview: The Patent Pending BPK-Probe™ is an easy to use instrument specifically designed to measure the risk for damage to motor bearings, gearboxes, or other devices that are susceptible to electrical discharges, also known as common-mode. These discharges are typically the result of

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