Current Hall Effect Sensors - Accuracy? (long)

Hi,

Specifically GRT supplied AMPLOC100 (green donuts). We have two and have been getting them installed and setup over the past days. The calibrartion numbers that we have recieved however seem to be rather off.

First question - if you have HE sensors - have you checked / calibrarted your setup - yes / no - results?

My test methodology: Take known current drain (land light = 6.4AMP) and run the cable X times through the donut. Use a sensitive fluke to measure the 'green wire' output voltage from the HE whilst using the EIS4000 for the Blue 4.8/5V reference and ship / common ground. The multiple pass through of the wires is just to be able to 'generate' an 80+ Amp load with a 6.4 Amp landing light.

Question - is this fundemental assumption about workings / testing of a HE valid?

The following Amp values are using the standard ScaleFactor=186 and ScaleOffset=-179 (EIS entered value as 357).

For background: Value=((Voltage*ScaleFactor)/2.5 ) + ScaleOffset


This is just so far out of whack that is it 'informational' at best, misleading at worst.

Question: Is this inaccuracy normal?
Question: Is this variation between 'identical' HE sensors normal?

I was under the understanding that HE should be an accurate measurement device (Maxwell's laws and all that). So after spending most of a day investigating and working various options, I found the B HE was pretty linear in sensing and using SF=1602 and SO=3057 (did you know EIS factors went THAT high?) with decimal values I get resulting values which are within .5 amp of measured (StdDeviation of .12) - really good and impressed with.


However with the A sensor tailing off at 60ish amps, it is impossible to get a decent calibration line for the whole range, so a rethink is needed there anyway.

So final questions: Are we on our own here, just one / a dodgy pair of sensors? Are we expecting too much? What checks / calibrartion have others done?

Thanks,

Carl

Bravo Man of experiment

I have the same amp100, EIS4000. I don't have the SF or Offset handy but found it to be pretty close. I did the same thing. I used a known load (like landing light) and a shunt / millivoltmeter to check the amps against the EIS4000. I admit I didn't go as high amps as you did. I'm using it on my alternators B-lead, and my alternator is only 40-45 amps, my max load about 30-32 amps. I was happy with a couple of data points between 1-12 amps and stopped there. It was pretty accurate and linear and assume the same in at higher currents.

Could one HE be bogus (bad)?

Thoughts...

Scott:

My understanding is no it doesn't have to be centered / anything special. Multiple cables all need to be going through the 'same' way.

No instructions on how to mount. Our approach was probably overkill - turned up a plastic bush that is then inserted in the center of the sensor.



George:

I'm thinking the 'A' side is suspect and otherwise it is manufacturing tollerances - but default values seem well outside what I was hoping for. Another option is to switch the A and B sides, the B side only needs to get to ~30Amps (SD-20) but changing them down the line is going to be a real PITA.

Any other datapoints people?

Carl

Yeah, nice job, Carl.

I don't have my GRT stuff yet so I don't know what they are using but have used hall donuts from FW Bell and Tamura, with and without internal electronics, and have found them to be pretty close from unit to unit with only trim calibration necessary. (Looking at a Tamura sheet, they are calling 1% linearity and +/- 1% FS accuracy, and its a cheapo, general purpose one) so the wide variation you are seeing is suspect.

BTW, looks like your 'A' device is just saturating at 'high' currents.

Hopefully, other GRT users will chime in with their settings and experience.. before I need to set mine!

John

PS. You are right, the wire does not have to be centered.

AmpLoc Spec Sheet

FYI: The AmpLoc site has details on the model that I think we have.....

http://www.amploc.com/AMP 25-300.pdf

And more general background / theory information
http://www.amploc.com/HANDBOOK 4.pdf

Carl,

I have to admit that I have never done anywhere near as controlled and detailed testing and calibration of the Amp sensor as you are doing, but my loads have always seemed "about right". I did have a situation a few months back when my dimmer module was shorting, and popped the circuit breaker. I did a test (on the ground!) by watching the amp meter while pushing the 5 amp breaker in. The amp reading went up by exactly 6 amps and the breaker popped, so I know I have about the right order of magnitude.


I'll be honest - I personally don't use the amp meter for much, as the experiences I have had with in flight electrical failures have all been extremely evident in the voltages. In the Valkyrie, I don't have any limits set on the Amps right now.

You're in the classic situation of the man with two watches right now - with two indications, you have no idea which one is right. With three, you'd have a tie-breaker, and with one....you'd have nothing to worry about!

Paul

Another data point.

I know this is a very old thread but I have just been through the process of calibrating the GRT Hall effect current sensor. I'll add my data point to this.

I will install the unit with two turns through the sensor to give me a range of +/-50 Amps.

Initially to get the resolution to 0.1 Amps I set the scale factor to 930 with Offset 1807 (sorta in accordance with GRT info, with SF x10 and offset adjusted out). Result was a 12% over reading, ie +1A read as +1.12A, -1A read as -1.12A. This is similar to the results at the top of this thread.

After a fair bit of experimentation I have settled on SF of 805 and Offset of 1563. This seems to be good to within +/-0.2A.

Reference was a calibrated Fluke87.
Doug

Update

Hi,

Wow, this goes back a bit.... but I didn't update the result. Yes I had a bad donut - GRT mailed a wararntee replacement.

Just looking at my configuraiton documention, the values I ended up with - and I believe are accurate for my particular units.

Channel SF Offset Direction Int/Dec
AMPA 1580 2939 + Dec
AMPB 1578 2991 + Dec

Regards,

Carl