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### Topic: Large Current Sensing with LEM sensor (Read 1 time)previous topic - next topic

#### dayta_eng

##### Mar 07, 2013, 10:42 pm
Hi all,

I am looking for some assistance in setting up a current sensor with an arduino due.

I would like to use this part (100A PN)  http://www.lem.com/docs/products/hais_e_rev11.pdf

From what I understand I will supply the sensor with 5V from the DUE.
What I am unsure about is the VREF and how to convert the readings to suit the 3.3V range of the analog pins on the Due.

From what I understand VREF can be both a driven input or an output??

When not driven VREF is an output voltage of = 2.5V+/- 0.025??

The voltage output of the sensor will be equal to VREF +/- (0.0625*I/100)
So Vout max (300A) = 4.375V and Vout min (-300A) = 0.625V

As this exceeds the maximum voltage I can put into the analog pins of the due then I think I need some sort of potential divider to lower the Vout max to 3.3V at 300A.

The problem I have is I can not seem to figure out what the output current of the sensor is. Do I use the output internal resistance value of 5 Ohms? In which case my output current is 0.125A to 0.875A and then work out my divider resistors to give a range of 3.3V to 0V?

Also is my assumption about VREF correct? Do I need to just measure it to check it is 2.5V and use it in my calculation of Vout or do I need to supply VREF in some way from the Due?

Any help would be much appreciated as I think I have taken it as far as my own knowledge can!

Chris

#### Erdin

#1
##### Mar 08, 2013, 12:25 amLast Edit: Mar 08, 2013, 02:46 pm by Erdin Reason: 1
This is the page for the sensor, http://www.lem.com/hq/en/component/option,com_catalog/task,displaymodel/id,64.83.34.000.0/

You have to search the whole site for documents how to use it.
Look for "hais" on that page.

Or on other sites, http://chyvack.ru/opisanie-acp-national-semiconductor-adc161s626cimm-i-datchika-toka-lem-hais-100-p.html

You could connect both the output and the reference to analog inputs. So the Due knows what the reference is.

For a full scale, you need a resistor divider or opamp.
I think that a resistor divider of 10k (to the 5V signal) + 15k (to ground) will work.

#### dayta_eng

#2
##### Mar 08, 2013, 02:19 pm
Thank you, I will be sure to look further than the supplier data sheets next time!

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