About Lem current sensor

LEM current sensors are magnetoresistive current sensors and hence can work both AC and DC current. There is a thick conductor on the sensor which carry current and above that is a coating of magneto resistor, which change value on magnetic lines of force passing through it. Other electronics is to amplify the sensed signal. These sensors can sense DC to 100kHz or even more speedy change in magnetic field due to electric current and hence are excellent for monitoring the switching power supply current pulses. Good thing is that sensor element is isolated like a transformer even for DC current sensing which is not possible to sense CT current sensors.

Mr. Shyam, LEM current sensor has different sensitivity depending from direction relative to conductor with current? Thanks for info, Nic

Yes the sensor is sensitive to direction. Now giant magneto-resistors are also made that are sensitive to magnetic field to very small level. Some people also used Hall Effect sensor for sensing magnetic field and often sensor is placed in cut portion of the magnetic core.

sir

can these sensors measure small currents in range of 500 mA to 3000 mA.If yes then at what frequency will they work to sense the small flux produced by such low currents.

500mA to 3000mA is not a small current and sensor can measure at kHz speed.

Sir

We are trying to develop a non-contact type current sensor for our project.Will induction principle work at low currents with frequency in microseconds.We actually want this sensing equipment for measuring the current flowing in a bus in devices like printers.This equipment is only for testing hence we don't want to mount this sensor on the board.Will a single turn transformer with air core work for such currents.What is the best way to develop such a sensing device.

Experiment and see.

Sir,

I want to sense three phase currents of peak 4.15amps using HX 05-P

I am using PWM technique with switching frequency 10Khz to get pure AC signal of 50 Hz. Have i selected the correct sensor. I want to get good results. Can you suggest me more better option.

ALso please tell how can I use "TWO" HX 05-P to sense "THREE" phase currents?

Thank you,

Yogesh.

yes. This sensor is Ok.

Dear Dr Shyam

thank you for providing some detail for the sensors.

can the sensors be used to senses electric and magnetic fields of a power cable (13.8kv and 60 hz) ?

can you send specification data and possible application

many thanks email : msmiai@kacst.edu.sa

web site : www.kacst.edu.sa

Hello mahalingam,

you should carefully think about your application when selecting a current sensor - when it`s a lo cost application where you only need rough results with higher tolerances and slower step response times you can use LEM, otherwise you`ll burn your fingers. This can be proved when you compare rms-results of LEM with a calibrator, par example FLUKE.
If you don`t need isolation and current range is <200A you should look at isabellenhuette.de, they build fine resistive precision sensors with lo inductance so that you come up to 200kHz or more with good compensation.

Regards Uwe

Our application is a simple one.

A Dc motor is there we have to find the current in open circuit and in short circuit.

Also we pass 500v single phase AC to the machine body and -Ve input of the DC motor to test insulation level.

For all the case we measure currents in a single LEM sensor.

That means we test rated voltage test 1st and short circuit test next.

Thats why i am asking we put two different currrent sensor (for AC and DC) or single sensor is enough.

I don`t know your motors DC current range but I think it will be in any way be much larger than the isolation current - assuming your isolation is ok. So I would measure the DC current with a sensor and, independly from that, the isolation current as a voltage over a resistor in series with your machine body, motor and isolation test voltage source.

For AC current, Current Transformer "CT" may be good enough and is a lower cost device. These can respond from 50Hz to few hundreds of kHz frequencies, arc discharges, dielectric breakdown and motor current fluctuations.

Have a really good look at the LEM site. Their explanations are very good. The closed loop Hall effect measuring modules they produce are illustrated and the ratings are published there. Some of the US manufactured devices are not listed though, but the Swiss built ones are. When I use them to analyse AC drives the picture is good enough to deconstruct the PWM output from the DC link current.