Level shifting in OPAMP and HE100T01 interfacing problem

Question

Hi,

I want to measure current of 0-50A. For that, in my application I am using HE100T01 hall effect sensor which can measure current from -100A to +100A(depending on the direction of flow it gives -ve and +ve values). The Hall effect sensor gives a current output of -50mA to +50mA. Since my micro controller ADC can't measure negative voltage, I tried level shifting the sensor output to positive region using the circuit which is attached. But the negative voltage is not properly clamping to the +2.5V offset. Can anyone please help me to identify the problem and also give any alternate circuitry to convert the sensor output which can be measured using a micro controller ADC?

Please find the datasheet for the Hall effect sensor and attached schematic. http://www.electrohms.com/data_pdf/2_1_HE100T01-05.pdf

Looking forward for earlier responses.

Regards,
Vishnu

Answer 1

On most op-amps you cannot properly use an input signal that is below the - supply pin. You might try to bias the sensor output to 2.5v (with equal pull up and pull down resistors on the sensor's output).

Alternately, to set up a true level shifting circuit see these examples that use hall effect sensors:

http://www.next.gr/sens-detectors/hall-effect/current-monitor-l13368.html

http://www.instructables.com/id/How-to-Measure-AC-Current-using-Hall-Effect-Sensor/