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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.

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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