Constant current source for electrical resistivity (ERT ) need help  - Page 1
Forum section: electronics / projects

author: Maxoverdrive
author_rank: Contributor
timestamp: July 22, 2021, 02:47:27 pm
content: HelloI have a very limited skill in calculation in this domain , I work on a ERT tomography home made systemI need a 150 DC ( 1.414x110 V ) with 150 mA and 250 mA current , can be two separate circuitcurrent will injected in soil during 0.25 second or 0.5 secondI have the DC source ( 220/110V transformer with rectifier and capcitor to get clean voltage ) available current is 1 Amp or more if needed .I have after hours of search on google I have located a lot of lectures / courses / ... on current mirror or current source but nothing as a clear exemple or already made circuits with information or even where to locate L and W value or how to calculate transcondunctanceDoes someone have an available design with BOM or at least component specs / valueA Wilson current mirror can be a solution ( transistor or Mosfet ) if I have values .Thanks in advanceRegardsMOD

author: ocw
author_rank: Regular Contributor
timestamp: July 22, 2021, 04:02:33 pm
content: For at least earth ground resistance measurements, I used the following publication to build my own tester:https://www.aemc.com/userfiles/files/resources/workbooks/950-WKBK-GROUND-WEB.pdfFor those sort of measurements I simply measured the current rather than making a constant current source. And, due to soil acting as a battery, using AC rather than DC will produce much more accurate results. Plus, your combination of voltage and current could be deadly if used incorrectly.I have since purchased five different commercial earth ground resistance testers.

author: Maxoverdrive
author_rank: Contributor
timestamp: July 22, 2021, 05:44:00 pm
content: Dear OWCThanks for the pdf linked that usefullI dont use pure continuous DC but a set of short pulses of DC linked with data acquisition on voltage received ( dipole dipole method the same method used for resistivity of metal ) to avoid to charge the soil , There are some articles on the net with this method .Right now I have a current limiter set on 200ma that work but my goal is to improve accuracy by injecting constant current and not get a current ramp up to reach 200 mAERT tomography equipement are $$$ but in my case that not usefull if I need a simple system so no complex management for 3D or multiples electrodes pitchs setup .Professional system go up to 500 VRegardsMOD

author: Marco
author_rank: Super Contributor
timestamp: July 24, 2021, 09:45:03 pm
content: This is a scary amount of voltage/energy being used. Do the electrodes have thick layers of rust which need to be punched through or something?

author: TimFox
author_rank: Super Contributor
timestamp: July 24, 2021, 09:55:33 pm
content: If you build a true constant-current source with high compliance voltage, be very careful! With no load current or high load resistance, the output voltage will go to the compliance limit, which can be dangerously high.

author: Marco
author_rank: Super Contributor
timestamp: July 25, 2021, 02:34:21 pm
content: Especially because it's fed through an inverter. A couple ms pulse every second might be survivable, but the inverter has power to put out a lot more.A little safety in depth would be nice for a device which exposes its high voltage, a single Watt high voltage power supply instead of a kilo-Watt plus inverter.

author: Maxoverdrive
author_rank: Contributor
timestamp: September 06, 2021, 01:41:45 pm
content: Hello@MarcoElectrodes are in SS304 to avoid oxydation , can be in copper too even copper with nickel coating to keep the same contact resistivity .@TimfoxThanks for the explanation , my main concern is that documentation is not easy to locate to learn , there is a lot of professional system on the markets but they are $$$ .soils have their one resistivity , there is two technologies Current control or Voltage control ( current-voltage (CV-ERT) (or current mode) and voltage-current (VC-ERT) (or voltage mode) ).ThanksMOD