Shaft Voltage Detection Device

Helwig Carbon’s 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. An optional tablet-style oscilloscope is available to record and analyze measured results.

Patent Pending



BPK-Probe™ FAQs

An instrument used to measure 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-ProbeTM 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.

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, etc… are all susceptible to damaging discharges due to common mode or static voltage discharge and should be monitored.

With the BPK-ProbeTM 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-ProbeTM Operating Guide for additional information on safe and proper use. Factory training is recommended, please contact Helwig Carbon for more information.

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 optional tablet oscilloscope or other 3rd party device to verify the test results. Reference the BPK-ProbeTM Operating Guide and Tablet Oscilloscope Operating Guide for details.

The ground cable and clamp included with the BPK-ProbeTM 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.

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-ProbeTM Kit. Replacement tips and brushes are available and stocked at Helwig Carbon.

Yes. In addition, the BPK-ProbeTM 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.

No, not on the probe. To save data use the Probe’s BNC output to capture test results on the optional tablet oscilloscope or other 3rd party device. These devices can save and download captured data.

Version 1 of the BPK-ProbeTM does not have wireless capabilities.

Helwig offers an optional “Remote Probe Interface” to allow test/verification of the performance of an installed BPK kit. The Remote Interface allows the motor shaft to be tested using the BPK-ProbeTM 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 down time, etc. Please contact Helwig Engineering for more information.

Helwig does not recommend using the BPK-ProbeTM or any other instrument in explosion proof or otherwise hazardous environments. Follow all safety precautions and regulations when using the BPK-ProbeTM. 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 (www.helwigcarbon.com) for more information or to schedule a visit.

The BPK-ProbeTM 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-ProbeTM. 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 probe kit includes Operating Instructions for both the BPK-ProbeTM and the optional 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 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.

Operating Manuals & Safety Information

BPK-Probe™ Shaft Voltage Detection Device Operating Guide

Tablet Oscilloscope Operating Guide

BPK-Probe™ Blog Posts

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

Why We Test For Shaft Voltage (And You Should, Too!)

Bearing discharges damage the motor bearings in two ways: the degradation of the bearing grease the roller assemblies are suspended in, and by electrostatic machining (ESD) of the bearings and bearing raceways. The combination of the two can be devastating to the life of the motor bearing and should be mitigated to avoid costly repairs and machine downtime.

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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