Shopping cart

Precision USB 50 kV probe

  • Excellent accuracy: 0.01% typical from 0 to 50 kV
  • Handles DC voltages to 50 kV
  • 1,000 MΩ input impedance
  • Temperature coefficient under 50 ppm/°C
  • Compact profile: only 12 inches in length
  • Compatible with all CPS probe tips

Model 255 is a USB 2.0 compatible high voltage probe that measures DC voltage up to 50 kV with very high accuracy. Unlike conventional analog probes, it requires no meter-dependent compensation or divider ratio. Model 255 does not measure AC voltage.

Model 255 high voltage probe connects directly to a laptop computer for flexible high voltage measurement and data logging

It employs a high resolution digitizer and embedded processor that work together to greatly reduce sensitivity to voltage coefficients and temperature variations, thus largely eliminating the primary sources of error found in purely analog probes. For higher voltage applications, the model 505 100 kV USB probe is also available.

The probe's unusually short length is made possible by our oil-free, state-of-the-art epoxy encapsulation technology. DC calibration data is traceable to NIST primary standards. Its outstanding accuracy and compact size make it ideal for calibrating, monitoring and testing a wide range of high voltage equipment, including power supplies, CRT display systems, microwave systems, and nuclear instrumentation.

Digital interface

Model 255 combined with a user
supplied tablet computer to make
a portable, precise high voltage
measurement system

The probe's built-in data acquisition system is entirely USB powered. It simultaneously measures high voltage DC, high voltage RMS AC, and internal temperature, and detects peaks in high voltage DC. The resulting digital values are sent over USB to a user supplied host computer for display, recording, or analysis, as required by the application.

If desired, two or more probes can be connected to different USB ports on a single computer and used at the same time. Free demo programs are available for user supplied Windows and Android hosts, and an API is provided for custom application development.


The probe includes an attached grounding cable which, when connected to a suitable ground potential, protects the operator and measurement system from high voltage exposure. An audible warning sounds and a visual indicator lights if the probe tip is brought near high voltage while the protective ground is unconnected.

A high voltage bell is integrated into the probe body between its handle and high voltage tip to increase the surface path length, effectively increasing the distance between operator and high voltage.

Probe tips

A variety of interchangeable probe tips are available to meet a range of application requirements. The probe's high voltage end has a threaded opening that allows standard CPS tips as well as custom tips to be easily attached. Two additional threaded openings are provided in the high voltage bell to allow the probe to be securely mounted to a measurement system.

Included Accessories

  • 1-corona ball tip
  • 1-pointed tip
  • 1-connector insert
  • 1-USB cable

Probe Tips

Three standard, interchangeable tips are available:

PN Image Description
250B Corona ball tip. This probe tip has a large radius of curvature that helps to minimize arcing to the tip when making and breaking high voltage connections. The contact end has an opening that serves as a jack for standard banana plugs. A connector insert (PN 250S) is required to attach this tip to the probe.
250P Pointed tip for probing circuitry in confined spaces where a corona ball won't fit. The contact point has a moderate radius of curvature to reduce arcing, and extended length to allow selective probing. A connector insert (PN 250S) is required to attach this tip to the probe.
250H Hook tip. This tip allows the probe to hang on a suitably shaped high voltage electrode for hands-free operation. It screws directly into the probe and does not require a connector insert.
250S Connector insert. A connector insert is required to attach the probe to a 250B or 250P probe tip. One end screws into the probe and the other into the probe tip. A single insert can be shared by multiple tips, though it's handy to have two if the tips are changed frequently.

Protective Case

The probe is a precision instrument that should be protected when not in use. An optional instrument case is available for this purpose:

PN Image Description
252CASE Instrument case. This sturdy case will accommodate a probe, a complete set of probe tips, connector inserts, and instruction manual. It securely holds the probe and accessories in a shock absorbing, custom fitted molding. The hinged handle allows for easy handling and compact storage.

Viewing Block

For applications up to 30 kV, this viewing block provides a convenient way to make a three-way connection between probe, power supply and load:

PN Image Description
HVT30 Viewing Block. This unit provides a convenient and safe way to connect your probe to a HV power supply (up to 30 kVDC) and load. It also provides a surge-protected, AC-coupled output jack that can be connected to an oscilloscope or AC voltmeter for ripple measurement.
Maximum voltage±50 kVDC peak
Input impedance1,000 MΩ/10 pF
DC meter
Measurement range-50 to +50 kVDC
Initial accuracy±5 V maximum error
Temperature coefficient12 ppm/°C typical, in range 15 to 25°C
AC meter
Measurement range0 to 50 kVAC RMS
Frequency range10 Hz to 10 kHz
Initial accuracy0.1%
Temperature coefficient50 ppm/°C typical, in range 15 to 25°C
Operating temperature0 to 40°C
Altitude< 2000 m
Relative humidity (max)80% at 31°C, 50% at 40°C
Output connectorUSB, Mini-B
Weight1.8 lb
DimensionsView mechanical drawing
Product manualModel 255 Instruction Manual
Windows SDKModel 255 Software Development Kit for Windows
Linux SDKModel 255 Software Development Kit for Linux
Windows DemoModel 255 Demo Program for Windows
Android AppModel 255 Android App
Model Description Price Order Qty.
1 2–9
HV Probes
255 Precision USB 50 kV probe $677 $615
included Each probe ships with one 250B, 250P, and 250S (250H not included) $0 $0  
Probe Tips
250B HV probe tip, corona ball $47 $47
250P HV probe tip, pointed $18 $18
250H HV probe tip, hook $14 $14
250S HV probe tip connector insert $2 $2
Probe Cases
252CASE Storage case for 50 kV probes $175 $175
USBCBL 72-inch Cable, USB A-Mini to B $10 $10
Viewing Blocks
HVT30 30 kV viewing block with AC-coupled out $600 $600