It looks like a reasonable solution for isolating scopes for measuring anything in circuit and mains referenced equipment. I was really surprised that rfloop nor Tautech had not mentioned anything about this thing with all the discussions about isolation and differential probes. Maybe I missed it.
You did.
Recently posted in a thread started by
nctnico:
https://www.eevblog.com/forum/testgear/isolation-amplifiers-(for-oscilloscope)/msg724098/#msg724098I have wanted to do a full thread on this
Isolated
Front
End and I still might
but the attenuation of ISFE has not matched the probe attenuation settings available on all Siglent DSO's.
AFAIK this is about to change in future FW upgrades and add 2 to have a full 1, 2 ,5 range of probe attenuation.
When released the new SDS1000X series DSO's will have 1, 2, 5 probe attenuation so OSD measurements WILL be accurate with the ISFE.
For simple measurements ISFE is a neat, cheap safe product that gives users
2 isolated channels for far less cost than 1 differential probe.
For other DSO brands ISFE users should consider these points:
ISFE is USB powered. (*below email lists PC, this was done so screenshot could be captured to USB stick)
ISFE BNC connector spacing allows for DSO connection with supplied double ended BNC plugs that may not suit the spacings for some DSO's.
BNC cables would/could then provide the necessary connection to Ch inputs.
For accurate OSD measurement the DSO must have a 200:1 probe attenuation setting
Probes with
insulated BNC connectors should only be used as the Reference lead AND BNC connectors will be an DUT potential.
(this is when the GND lead should NEVER be referred to as GND but instead
Reference)
Siglent supplies with all their DSO's, insulated BNC probes for safe use with the ISFE.
Email to Siglent re ISFE attenuation:
Hi Jade
When I visited Siglent China I had a discussion with Wells on the ISFE attenuation.
The 200x does not match any input settings for Siglent DSO’s.
This makes any on-screen measurement inaccurate.
The ISFE is a good product for its intended use: isolation.
But to market it aggressively the 200x attenuation will be a problem.
I see 3 solutions:
1. Add 200x attenuation in all DSO firmware. Without knowledge of the attenuators, I am not sure if this is possible.
Do you know?
2. Adjust the attenuation in the ISFE to match available attenuation on Siglent DSO’s.
3. Add a “Siglent ISFE” option (200x) in the Probe menu with fine adjustment for additional accuracy of measurements
Manual states 2 important things for the intended use of ISFE.
1. Isolation for floating measurements.
How can accurate measurements be taken if attenuation of ISFE and DSO input are not the same?
2. Used to test high voltage.
Floating measurements are also needed for some low voltage work, this must not be overlooked.
I see the ISFE input impedance is 9 M Ohms and BNC to Alligator clip leads are supplied, so this implies a 1:1 probe connection should be used
Tests indicate a 10:1 probe produces an incorrect waveform.
It need be stated in the Manual “for 1:1 connection”
Very Simple Test
Please see attached and/or copied image:
Incorrect measurements are obvious.
Notes
SDS2304 Probe Cal output ~3V p-p @ 1KHz
All Ch 20 M bandwidth limit ON
DC coupling
All Channels set to 1V/div
256 Average ON
ISFE Channels set to GND as in manual
Ch 1 Siglent 300MHz DSO probe 1:1
Ch 3 ISFE and Siglent DSO Probe 1:1 DSO input set to 100x
Ch 4 ISFE and ISFE alligator lead 1:1 DSO input set to 100x
*ISFE power supplied from PC
ISFE coupled to 2304 with supplied BNC to BNC connectors
Why 3 V test?
Small SMPS may use 3 V and isolated connection may be required.
Comments
Solutions to measurement errors earlier mentioned.
Ch 3 using Siglent probe shows better reproduction of the waveform than ISFE Alligator to BNC cables.
Please consider my comments as very important issues for Siglent to consider re ISFE.
Kind Regards
Tautech