ADF25A High Voltage Differential Probe



Permits conventional grounded oscilloscopes to be used for the display and measurement of multiple floating signals with high common mode voltages
  • IEC1010 approved for safety
  • Wide bandwidth DC-25 MHz
  • Up to 1000 V RMS
  • High common mode rejection

ADF25A High Voltage Differential Probe for DSO
Differential probe for Oscilloscopes

Typical Applications

These probes are ideal for use in measurement of switched mode power supplies, motor control circuits, process controllers and in many applications where it is required to measure voltages which are floating with respect to ground.

The ADF25A will accept up to 1000 V RMS differential and common mode voltage. The probes can withstand their rated common mode voltages on either attenuation range without damage. It is therefore possible to observe small signals superposed on large common mode voltages be selecting the lower attenuation range. This is useful, for example, in measuring and observing small gate signals of semiconductor devices which may be several hundred volts above ground.

Although the probes are primarily designed to enable use with ground oscilloscopes, they may also be used with insulated or battery operated oscilloscope; but with such scopes the probe output lead still must be grounded using the ground lead supplied.

The input leads of the ADF25A have standard sleeved banana plugs which accept standard push-on accessories.

Floating Measurements Made Simple

The ADF25A is an active oscilloscope probe which permits differential measurements to be made with a conventional grounded oscilloscope. The probe is approved for IEC1010 Category III for safe use on heavy-duty motors and similar circuits. The probe incorporates a dual balanced differential switched attenuator system which is combined in a single ended output which can be fed directly to a one channel of an oscilloscope. This method significantly reduces the errors associated with separate probes and scope channels, and gives improved common mode rejection.

The use of additional probes on a multi-channel oscilloscope with common time base permits the viewing of multiple floating wave forms (e.g. for three phase measurements).

The probes can be powered from 4 internal AA batteries or from an external 6V power adapter (not included). Because the output and power connections are ground referenced and separated from the differential inputs, a specially isolated power supply is not required and two or more probes may be powered from a standard power supply.


Input Voltage
Max. Differential

± 70 V (AC + DC) @10:1 or 50 V RMS
± 700 V (AC + DC) @100:1 or 500 V RMS

Common Mode Max.

± 1400 V (AC + DC) or 1000 V RMS

CMRR (typical)

1 MHz



100x setting: DC -25 MHz (-3dB)
10x setting: DC -20 MHz (-3dB)


± 2%

Rise Time

100x setting: <=14ns
10x setting: <=18ns

Input Impedance

4 MΩ /10pF each side to GND
8 MΩ /5pF between inputs

Output Source Impedance

± 7V (minimum 2 KΩ load)
< ± 5 mV (-10 °C to +40 °C)
1.5 /2mV
1 Ω @ 1KHz, 8 Ω @1 MHz;

Operating Temperature

-10 °C to 40 °C

Power Requirements

4 AA cells or 6V DC/60 mA power supply

Input Leads

45cm double insulated PVC terminated in 4mm safety plugs

Sprung Test Hooks

1 red, 1 black sprung hook

Output Cable

95cm RB58 C/U terminated with standard BNC plug

Weight (w/o batteries)

0.62lbs (285gm)


6.6" x 2.4" x 0.8" (166mm x 62mm x 20 mm)

IEC 1010 Compliance

Category III


  • $319 Probe Kit (includes probes, power supply, red and black hook clips, carrying case)