Open loop fluxgate current sensor? - Page 1
Forum section: electronics / beginners

author: Faringdon
author_rank: Super Contributor
timestamp: September 07, 2021, 05:59:32 am
content: Hi,Has anybody ever heard of an open loop fluxgate current sensor?The key words being "open loop"

author: GeoRock
author_rank: Newbie
timestamp: September 08, 2021, 08:26:01 pm
content: Have a look at the DRV425:https://www.ti.com/product/DRV425There is also an evaluation module:https://www.ti.com/tool/DRV425EVMBeen developing a project with this, it's a nice little sensor.

author: Faringdon
author_rank: Super Contributor
timestamp: September 10, 2021, 11:15:11 am
content: Thanks for that, looks really good.As you know, DRV425 is "closed loop" in so far as it has an internal compensation coil which is driven so as to bring the current waveform "symetrical" about zero amps)Also, its a shame it couldnt really be used to sense say 6mA of DC leakage in a 32Arms distribution system. Also, i doubt it would be able to accurately detect 30mA of imbalance current in the said same.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 10, 2021, 01:12:45 pm
content: If it is about detecting only the leakage part, that is the difference in 2 currents, than the high of the main current does not have much influence. With 2 wires through the same core one would only see the difference. The high main current only needs a sufficiently large opening / core.There are ready made current differential current sensors that also work for DC.An example is this one, sold for cheap in Germany:https://www.pollin.de/p/differenz-stromsensor-vacuumschmelze-t6040n4646x95081-300-ma-5-v-180071It the wires for thmain 35 A current fit through the opening, all is fine.There are also more expensive DC current transformers with a larger opening an more accuracy.The DRV425 is compensating locally at the sensor, but would not be compensating the main current. However the core or distance to the conductor would have an influence.

author: Terry Bites
author_rank: Super Contributor
timestamp: September 10, 2021, 02:59:38 pm
content: Right up your street, Current Transducer CDSR 0.07-NPRogowski sensors are very low noise sensitive.They are open loopshttps://www.rammeter.com/accuenergy-rct24-rogowski-coil-flexible-current-transformer-24-coil-w-7-00-window

author: Faringdon
author_rank: Super Contributor
timestamp: September 11, 2021, 10:18:12 am
content: QuoteThanks, sorry i am struggling with my German for some of that...is there an english equivalent web page of this?QuoteThanks, i emailed LEM but they wont quote me unless i give project details which i am not at liberty to give. Do you know the price?My German was failing me a little, but the T60404-N4646-X950 seems to do the same as what the LEM "CDSR 0.07 NP" does, but likely costs a lot less (i assume CDSR 0.07 NP is expensive given that LEM wont tell me the price without me giving them loads of confidential project info

author: Kleinstein
author_rank: Super Contributor
timestamp: September 11, 2021, 11:24:54 am
content: Here is a link to the nanufactuers info in english:https://vacuumschmelze.com/Assets-Web/World_of_VAC_Current_Sensors_Sep%202019.pdfThe price in the German web shop is not a regular price, more an special offer for left over stock.In side the sensors look relatively simple with a magnetic core made from more L shaped laminations. So the electronics could also handle a movable more clamp like core.

author: Faringdon
author_rank: Super Contributor
timestamp: September 11, 2021, 07:05:50 pm
content: Thanks,the T60404N4641X900 is the one we are after....https://www.digikey.co.uk/en/products/detail/vacuumschmelze/T60404N4641X900/12530335..it is $30 in qty of 50.It does the "6mA/30mA" thing so that must be the reason that its more expensive than the T6040N4646X95081