ITTSB.EU Blog Forum
Electrical Test and Measurement instruments => Bench-top Oscilloscope & Handheld scope meter => Topic started by: Kiriakos GR on February 10, 2026, 04:58:28 PM
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Indeed, Oscilloscope digital Low-pass filter, this saves the day but causes delay. :)
This period of time I have started a new series of tests, of Low current and ACA measurements at 50~400Hz.
By connecting TA189 probe at my GDS-2102A, I did notice that AC current measurement this was full of noise.
This time I am not using any current coil amplifier, as boost of current measurement.
This time I have to deal with Oscilloscope Noise floor along of AC/DC probe noise floor.
The only way making my current probe to function properly with my oscilloscope, this was by activating it digital Low-pass filter.
Acquisition Setup -> FILTER
Now I have ACA measuring range since 10mA up to 30A. 8)
But I did sensed, that there is some time lag, when measured current this changes from a known value to another known value.
For example, from 55mA the load changes at 80mA = instant change, but from the side of the oscilloscope, the delivered measurement this becomes accurate after of three seconds of time.
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I did searched for relative documentation, and I did find an quick description from the side of Rohde&Schwarz
Lowpass filters reduce the speed of the signal inside the instrument and cause a delay of the signal on the screen.
Rohde&Schwarz even compiled at table, this delivering ms delay VS selected low-pass filter frequency.
Examples:
1 kHz / 4.347 ms
2 kHz / 2.173 ms
5 kHz / 869.3 μs
10 kHz / 434.7 μs
What is very interesting, this is the observation, that at multiples of 2 ( 2, 4, 6, 8, 10) the digital filter causes a smaller delay at the oscilloscope electronics. ;)
My Oscilloscope this is (GW Instek) GDS-2102A, I am unaware of this digital filter, actual caused delay per Low-Pass filter setting.
But electronics theory of operation, this is not much different between oscilloscope vendors.
For more than ten years, I were involved at product reviews, and never thought as feature for be bench-marked, the speed of digital Low-pass filter, between reputable vendors as is Tektronix VS Rohde & Schwarz VS GW Instek.
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At ITTSB there is also a similar article, with application examples.
Sensitivity of the current probe and oscilloscope combination too low (https://www.ittsb.eu/forum/index.php?topic=1767.0)
Either way, the combination of theory facts along of actual generated experiences, by using your equipment, this is all the assistance that you may get.