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LEM HLSR 10P current sensor

robals

Jan 24, 2017
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I'm having no luck getting anything out of this current sensor. I've hooked it up to something drawing about 5 Amps, powered the sensor with 5v and placed the necessary capacitors across the pins. The Vout should be higher than Vref when current is flowing but they are both about 2.5v whether current flowing or not. Also tried putting a lower voltage into Vref, about 2v, which just lowered the Vout voltage to the same and made no difference when drawing current.

Here is the info for the device...
http://docs-asia.electrocomponents.com/webdocs/1272/0900766b81272eb2.pdf

Has anyone had experience with these devices or know of another way to sense current? I don't need accurate measurement, just need to know if something is running or not (woodworking machinery like tablesaw, etc...)
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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Is the device your connecting it to run from AC? If so, the average output will be 2.5V, but it will vary equally either side of that value 100 times per second. If you're reading the value with a multimeter on a DC range you won't see this. On an AC range your meter may read it (a lot depends on your meter because you have AC with a DC offset). Measuring the AC voltage between the output and the reference if probably the best method with a multimeter. I don't suppose you have an oscilloscope?
 

robals

Jan 24, 2017
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Thanks Steve. It is running from AC. I don't have an oscilloscope. I have since tried putting an LED between Vout and GND and it lights up when I draw current through the sensor, so at least I know it works. I suppose if I plug Vout and Vref into a voltage comparator like LM311 I'd get a nice clean signal out I can use to switch something? Please excuse my lack of knowledge, I'm more of a woodworker than an electronicist. Thanks again for your help.
 

hevans1944

Hop - AC8NS
Jun 21, 2012
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Please bear in mind that this transducer is similar to the Allegro Hall-Effect sensor. It responds to both positive and negative current directions through its input terminals, with an offset of about 2.5 V DC when the input current is zero. Thus an AC input current will cause an AC output with a DC offset. The DC offset is what lights up your LED when you tested the device. If you want to measure the AC current, the easiest way to do that is to couple the AC+DC offset output through a capacitor to remove the DC component. Rectify and then low-pass filter the AC component to remove ripple, and then measure the resulting DC voltage or apply it as one input to a comparator if you want to switch at a particular AC current input level.

Another woodworker here has extensive experience with the Allegro version of this device and may want to chime in with further advice.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Another option is to use a bridge rectifier and pass pulsed DC through the sensor
 

robals

Jan 24, 2017
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Thanks for the suggestions, I'll give them a try and see what happens!
 

hevans1944

Hop - AC8NS
Jun 21, 2012
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Another option is to use a bridge rectifier and pass pulsed DC through the sensor
Clever idea, but the diodes defeat the ultra-low resistance (a few milliohms) for which this type of device was created. Should work though if one can "tolerate" the voltage drop across the bridge and subtract the DC offset in the output.
 
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