fix current sensor - Page 1
Forum section: electronics / beginners

author: littlebill
author_rank: Regular Contributor
timestamp: June 09, 2015, 12:05:07 am
content: hii bought this.http://www.ebay.com/itm/400770304649?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AITwhen measuring a load of 2.25 amps, it reads out 1.51 amps.is there a way to fix or adjust this?

author: littlebill
author_rank: Regular Contributor
timestamp: June 09, 2015, 01:40:29 am
content: i fixed this, by putting a offset in the math portion of the software, and now it tracks perfectly. that said is there a way to fix this hardware wise? or is this generally how you calibrate these type of sensors? its tracking perfect now to .05ma resolution

author: mikerj
author_rank: Super Contributor
timestamp: June 09, 2015, 12:43:11 pm
content: Since you have only shown us one part of your current measurement device (i.e. the sensor) it's difficult to comment. Have you measured the voltage output of the sensor with a calibrated multimeter whilst passing your 2.25Amp load current to rule out any issues with the rest of your circuit or software?

author: littlebill
author_rank: Regular Contributor
timestamp: June 09, 2015, 02:36:12 pm
content: yes i used 2 amp meters in line between the shunt, it showed .01 difference between the meters.not sure what else needs to be seen, simply reading the analog reading off the current monitor. wired directly to constant current power supply using a spring as a resistive source.after adding a .66 correction factor to the amp conversion, it tracks at .01 the same as the other 2 load meters.

author: mikerj
author_rank: Super Contributor
timestamp: June 09, 2015, 02:44:22 pm
content: Quote from: littlebill on June 09, 2015, 02:36:12 pmYou haven't even told us what voltages you are getting from the sensor. If you measure the output voltage for at least two known currents (e.g. 0 and 2.25Amps) and plot the transfer function, are you saying this falls outside of the datasheet specification? Ignore the rest of your system entirely, since we know nothing at all about it.

author: German_EE
author_rank: Super Contributor
timestamp: June 09, 2015, 03:06:07 pm
content: I wonder why they refuse to ship to Germany and the Repuplic of Ireland (amongst other countries)?

author: bobcat
author_rank: Regular Contributor
timestamp: June 09, 2015, 07:42:22 pm
content: The output voltage is centered around 1/2 Vcc.So, for zero amps you should see 1/2 Vcc.

author: littlebill
author_rank: Regular Contributor
timestamp: June 09, 2015, 09:27:10 pm
content: Quote from: mikerj on June 09, 2015, 02:44:22 pmSorry,not trying to be difficult, not really sure what needed to be provided.this thing is hooked directly to an arduino via the 5v/Grd/A1 input ports.at 0 current it reads 2.5v which is perfect.the load which is a simple spring is feed power via a current controlled PSU.readings from both meters, were showing 2.25 amps. the shunt showed about 1.51, and it scaled roughly the same through the entire range i could try 500ma-5 ampsfrom some reading this appears to be normal that a correction factor is needed.

author: mikerj
author_rank: Super Contributor
timestamp: June 11, 2015, 10:41:34 am
content: Quote from: littlebill on June 09, 2015, 09:27:10 pmAre you saying that with a current of 2.25Amps passing through the sensor, you measure 1.51 volts at the sensor VIOUT pin using a DMM? If so this is miles out of specification for the 5Amp version of the ACS712, let alone with 30 Amp version.If you are saying that your Arduino is reporting 1.51 amps then this means little to us, as we don't have a schematic for your system or the code etc. so no-one could say if you are doing something wrong. This is why a voltage reading on the output of the sensor would tell us if the problem is caused by the sensor or the rest of your system.Note that the transfer function of these devices has quite a wide spread (63 to 69 mV/A for the 30 amp version) so you will need to calibrate every sensor to get accurate readings rather than just using the nominal value in the datasheet.