P4100 100:1 High Voltage Probe: Safe Scope Measurements
By Kunkune | Published: 2026-11-03
Category: How-to Guides
Use the P4100 100:1 high voltage probe safely: set scope attenuation, compensate the probe, connect ground first, and stay within its 1000V rating.
Quick answer
Use the P4100 100:1 probe only with your oscilloscope set to the correct attenuation and never exceed its 1000V rating. Compensate the probe before measuring, connect the ground clip first, and treat the probe tip as live whenever the circuit is powered.
Why a 100:1 probe changes your measurement setup
A 100:1 probe divides the signal by 100 before it reaches the oscilloscope, so a 500V signal appears as 5V at the input. This protects the scope and extends its usable voltage range, but it also means you must adjust the scope's attenuation setting to match. If you leave the scope set for a 10:1 probe, every reading will be ten times too high.
The P4100 is rated for 1000V and has a 100MHz bandwidth, so it suits mains-derived and other high-voltage circuits within that limit. It is not a substitute for proper isolation or a differential probe when neither side of the circuit is grounded.
When a 100:1 probe is the wrong choice
For low-voltage logic and audio signals, a 100:1 probe attenuates the signal so much that noise and scope resolution become a problem. Use a 1:1 or 10:1 probe instead. Also, the P4100 is a single-ended probe, so it cannot safely measure across two live conductors in a floating or high-side circuit; use a differential probe or an isolation transformer for those cases.
Step-by-step: safe high-voltage measurements with the P4100
- Set the scope attenuation to 100:1: Before connecting anything, change your oscilloscope's probe setting to 100:1 or manually set the vertical scale to account for the 100x division. Common mistake: leaving the scope on 10:1, which makes the displayed voltage ten times too high and can mislead your safety decisions. Double-check the attenuation setting every time you change probes.
- Compensate the probe: Connect the probe tip to your scope's calibration output and adjust the compensation trimmer with a non-metallic tool until the square wave has flat tops. The P4100's 10-35pF range fits most scopes. Common mistake: skipping compensation, which distorts fast edges and gives false rise-time readings. Compensate whenever you move the probe to a different scope or channel.
- Connect the ground clip first, then the tip: With the circuit powered off, clip the probe's ground lead to the circuit ground, then power up and touch the tip to the test point. Common mistake: connecting the tip first and then fumbling for ground, which risks shorting a high-voltage node through the probe body. Treat the probe tip as live whenever the circuit is on.
- Verify the reading against a known source: If possible, measure a known voltage within range to confirm the attenuation and compensation are correct before probing critical nodes. Common mistake: assuming the probe is accurate without checking, especially after swapping scopes or channels. A quick sanity check prevents chasing phantom faults.
- Disconnect in reverse order and discharge: Power down the circuit, remove the tip first, then the ground clip. Wait for capacitors to discharge before touching the probe. Common mistake: leaving the probe connected while moving the circuit, which can create accidental shorts or shocks. Store the probe with the tip covered and the cable loosely coiled.
Product facts
- P4100 High Voltage Oscilloscope Probe 100MHz 100:1 – 1000V Rated: Rated for 1000V with 100MHz bandwidth and 3.5ns rise time. This covers many high-voltage measurements while preserving enough speed for fast switching edges.
P4100 High Voltage Oscilloscope Probe 100MHz 100:1 – 1000V Rated - P4100 High Voltage Oscilloscope Probe 100MHz 100:1 – 1000V Rated: Adjustable 10-35pF compensation range. You can match the probe to your oscilloscope's input capacitance for accurate pulse shapes.
