Isolation amplifiers?? (for oscilloscope) - Page 1
Forum section: electronics / testgear

author: nctnico
author_rank: Super Contributor
timestamp: August 04, 2015, 09:48:55 pm
content: I'm looking into getting some isolated channels on an oscilloscope. For example to look at the gate drive signal of a high side mosfet. I know there are differential probes but these also attenuate the signal. What I would want is the ability to measure a few volts riding on top of a couple of hundreds volts.So far I have found an isolation amplifier made by Siglent but that only goes to 1MHz. Are there any other options out there?

author: MagicSmoker
author_rank: Super Contributor
timestamp: August 04, 2015, 10:56:08 pm
content: Aside from an oscilloscope with properly isolated inputs, the only reasonable option to probe line-side signals in a SMPS is a differential probe. The usual differential probe with 25MHz bandwidth will faithfully reproduce "square" waves with a ~15ns risetime which ought to be more than sufficient.That said, I use two different scopes with truly isolated inputs for most of my work on switchmode power circuits - an ancient, but much beloved Tek THS720 and a newer but not as much loved AEMC OX7104. I also have a couple of B&K Precision 25MHz differential probes but they spend most of the time draining AA batteries (but do work well when used).

author: tautech
author_rank: Super Contributor
timestamp: August 04, 2015, 10:57:59 pm
content: Correct, however the Siglent ISFE is a 2 channel accesory that offers good isolation and lower DUT loadings than many Differential probes. USB powered.http://www.siglentamerica.com/prodcut-fjxx.aspx?fjid=404&id=25&tid=1&T=2You should be aware it has a 200:1 attenuation and FW to match this to enable accurate OSD in Siglent DSO's is being rolled out in each FW update.I've had a lot to do with this FWand it was discussed at length when I was at the factory some months back.

author: 0xdeadbeef
author_rank: Super Contributor
timestamp: August 04, 2015, 11:10:53 pm
content: Testec offers quite a few differential probes. They are rebranded by Tektronix, Agilent/Keysight, Hameg, Lecroy, Yokogawa etc.http://www.testec.de/251.0.html?L=1My personal favorite would be this one:http://www.reichelt.de/Tastkoepfe-und-Zubehoer/TT-SI-9101/3/index.html?ACTION=3&GROUPID=5903&ARTICLE=132890&OFFSET=16&100MHz and switchable 10:1 or 100:1 ratio. Unfortunately a bit expensive. I hope to get find one on ebay for 300€ or so one day.

author: nctnico
author_rank: Super Contributor
timestamp: August 04, 2015, 11:42:43 pm
content: IMHO one of the problems with differential probes is the banana plugs & leads. That won't work for signals over a few MHz. I would like something I can connect a somewhat standard oscilloscope probe to (with touch safe BNC locking mechanism) and attach it somewhere in a circuit.

author: 0xdeadbeef
author_rank: Super Contributor
timestamp: August 04, 2015, 11:59:04 pm
content: Something like this?http://www.voelkner.de/products/96796/Chauvin-Arnoux-Mtx-1032-B-Differenzsonde.html

author: tautech
author_rank: Super Contributor
timestamp: August 05, 2015, 12:28:55 am
content: Quote from: nctnico on August 04, 2015, 11:42:43 pmThis you can do with Siglents ISFE.I attach an email that was sent to Siglent but has an overview of ISFE useage.

author: nctnico
author_rank: Super Contributor
timestamp: August 05, 2015, 12:33:45 am
content: I already looked at the ISFE but the bandwidth is only 1MHz and the 200:1 attenuation ratio limits the use enormously.

author: The Electrician
author_rank: Frequent Contributor
timestamp: August 14, 2015, 05:49:00 am
content: Quote from: MagicSmoker on August 04, 2015, 10:56:08 pmSlightly OT, but what don't you like about the AEMC OX7104?