Interface with hall sensor

Forum 2005-2010 (read only) Hardware Interfacing
1

Hi everyone,

I want to measure DC current with the CSLA2CD hall effect sensor.

The sensor have a voltage offset of VCC/2. Every amp on the wire adds 33mV.

I will have to add a voltage divider to be in the adc range and a zener for adc pin safety.

What is your opinion about that ? Is it right ?

Thanks in advance

Best regards

2

Hi,

the max. input for the ADC is 5V, so you can measure up to 2500/32 Amps = 78Amps. A voltage divider will also reduce the resolution of your measuring. A Zehner diode is a good idea, also a restistor of about 1kOhm between sensor output and ADC input, the Z-Diode placed direct to the ADC input.
If the range is not big enough, i think it is a better idea to use an opamp to subtract the VCC/2 voltage offset, this gives you up to 156Amps. Above there is a voltage divider or opamp gain below 1 necessary.

Best regards
Mike

3

To suppress the offset, i that the best way to do : http://soundlab.cs.princeton.edu/learning/tutorials/sensors/img47.gif
http://soundlab.cs.princeton.edu/learning/tutorials/sensors/img48.gif

I can also multiply the 33mv / amp to match the whole adc range :
for max 74 amp : Vhall = 2,442 V

If R1/R2 = 2, I will match the 10 adc bits.

V1 is the middle point between vcc and ground with resistor divider.

I can use the AD627 witch is great for instrumentation.

What do you think about that ?

Thanks in advance

Best regards

4

Why do you want to get rid of the offset in the hardware? Its there so that you can detect negative currents as well as positive currents.

I would read the ADC value into an integer and then subtract 512. A negative number means a negative current. You may need to adjust the 512 to get a zero reading for zero current but thats easier than trying to adjust a voltage to get zero for zero current.

5

Because I need as much precision as available and a wide range of input values. The adc have 4.89 mV / bit précision. If I use an opamp to match to the adc range, I have a wider range and a better precision (two times better) if I use a instrumentation opamp like ad627.

6

You can also increase the gain of the Arduino ADC by reducing the voltage on the AREF pin. From a quick look at the datasheet it looks like the minimum you can put on AREF is 1V (probably to keep the resolution above the noise level). This is a free 5x gain already.

7

Good idea ! You must use all the adc pin for the same purpose. This is not my case ! But it's a good way to do

Thanks