What's the best way to translate current in a DC loop into voltage referenced to - Page 1
Forum section: electronics / beginners

author: cdev
author_rank: Super Contributor
timestamp: January 27, 2017, 01:19:00 am
content: ground on my scope. Neither side of the controller is groundable, and my scope cannot float,Theres something being sent down it once a second that I'm assuming is data... There also may be some higher frequency stuff or it may just be RFI( I cant just use a resistor because neither side of the controller is grounded.)I am going to try a simple toroid with two windings - a transformer, and see what I get doing that. I don't have the time to build an opto isolator today.Does this look like anything people are familiar with? The controller board is made by Kanalflakt..

author: yashrk
author_rank: Frequent Contributor
timestamp: January 27, 2017, 02:21:14 pm
content: First of all share more info on your circuit, what exactly you want to do.By the information you have provided guess you want to measure current in a circuit. Why not just put a low value resistor in the loop and measure the voltage of it and let ohm's law do it's magic ?

author: cdev
author_rank: Super Contributor
timestamp: January 27, 2017, 04:40:39 pm
content: Neither side of the loop is groundable/referenced to ground..Its an expensive fan/heat exchanging ventilation controller that ventilates based on several presets which are fairly limited. I want to be able to emulate the controller eventually so a small computer with sensors can control it based on rules.By and large I do want to have it running, most of the time, just sometimes less and sometimes more. certain things outdoors make me need to turn it off.I have sinusitis- long story.Generally I sleep better when there is a small amount of ventilation all the time. But currently it doesnt have all the settings I need.Initially I dont want to change anything, I just want to see whats being sent so I can figure out which of the two devices is speaking when and what is being said, and why.Eventually I want to be able to have a small SBC talk to the fan box in its own protocol if I can figure it out beyond a shadow of a doubt. I dont want to damage anything.Does this sound like its potentially any known protocol? When there is no activity occurring (when the fan is off) this signal is sent once a second. Thats probably establishes the timing and when the controller wants the fan to do something it probably sends some variation back.

author: AndersJ
author_rank: Frequent Contributor
timestamp: January 27, 2017, 05:27:12 pm
content: Use a currrent probe.

author: cdev
author_rank: Super Contributor
timestamp: January 27, 2017, 05:35:02 pm
content: what is in a current probe, an electromagnet and a hall effect sensor?Can I build one?

author: AndersJ
author_rank: Frequent Contributor
timestamp: January 27, 2017, 05:46:28 pm
content: https://en.m.wikipedia.org/wiki/Current_clampIt is difficult to build.Or use the previously mentioned resistor,and measure differentially with two oscilloscope probes.

author: cdev
author_rank: Super Contributor
timestamp: January 27, 2017, 07:36:47 pm
content: DOH!thank youthat may work.

author: AndersJ
author_rank: Frequent Contributor
timestamp: January 27, 2017, 07:45:19 pm
content: Yes, invert and add channel 2.

author: suicidaleggroll
author_rank: Super Contributor
timestamp: January 27, 2017, 08:02:07 pm
content: Quote from: cdev on January 27, 2017, 07:36:47 pmMost (all?) scopes will let you plot the difference between the two channels, should be in the math menu or similar.

author: yashrk
author_rank: Frequent Contributor
timestamp: January 29, 2017, 06:27:49 am
content: As suggested putting a resistor in the loop is the simplest way of doing it, also you can use hall effect sensor ACS712 which will give a sine signal with its center at VCC/2. Depending upon the current, the peak voltage will increase or decrease.Check this link for more info <http://www.instructables.com/id/How-to-Measure-AC-Current-using-Hall-Effect-Sensor/>

author: Brutte
author_rank: Frequent Contributor
timestamp: January 29, 2017, 11:39:05 am
content: Isolated hall sensor is not a bad choice.And with lower common mode voltage, if you need bandwidth then you can use a rawopamp. Of course reference has to be tied to scope's GND.

author: cdev
author_rank: Super Contributor
timestamp: January 29, 2017, 04:13:47 pm
content: I need something more suited to milliamps or perhaps even microamps (data) (also faster- there may be higher frequency signals )I don't need raw current measurement in amps..I do have a bunch of older opamps in my junk box.. don't know if they are still good.

author: Brutte
author_rank: Frequent Contributor
timestamp: January 29, 2017, 05:25:33 pm
content: QuoteYou need to know the bandwidth, the differential mode and common mode voltages first.If it is 1uV Ethernet frame on a 10kVAC then obviously it can be more challenging than a 1V 9600_8N1 frame on a 24VDC.

author: cdev
author_rank: Super Contributor
timestamp: January 29, 2017, 05:50:54 pm
content: Maybe I can tell something from the audio domain..