filter

[holko]

Hi, im doind a project and im using a current sensor(acs712 30A) im using arduino as daq and reading converting  0.200A to about 1V. to obtain 1 V i have amplified it in formula(times 80). The sensor normaly gives 2.5V at 0A. but ist fluctuating a lot and i want to put some conditions. 

1- The formula should accept values only above 2.509V (not below)

2- The output of the formula should be able to be plotted on a graph(when i put filter im not being able to plot the graph

Thanks

[johnsold]

That device is not a very good choice fro measuring currents in the 200 mA range. The peak to peak noise is specified as about 106 mA, and that is with a 47 nF filter capacitor and a 2 kHz bandwidth.

Because of the noise it is certainly possible that you will get some negative readings even if your current is always positive.

The zero current output voltage is nominally hall of the power supply but can vary from device to device and with temperature. A fixed threshold of 2.509 V may work for one device at room temperature, but is not robust over device and temperature variations. Allegro does not exactly specify the voltages but you can get some idea from the temperature graphs and total error specification.

The sensitivity for that device is specified as 66 mV/A with a range from 63 to 69 mV/A.  That gives scaling factors of 79.4 to 72.4 for 1 V output at 200 mA. Your 80 is a little high.

In Range & Coerce can clip off your below threshold signals. I recommend using standard functions from the Numeric palette rather than the Express Formula node. 1. You can see exactly what numerical processing you are doing. 2. It is probably much faster (execution). This may not matter for your present application but could in some future situation.  3. Express VIs are rarely the best choice for implementing functions in LV. As you appear to be a student, I recommend that you learn to use the basic LV functions whenever possible.

Filtering can reduce the noise but it also reduces the repsonse time and introduces delay and phase shift.

Lynn

[akash24]

thanks for the advice, im facing a bigger problem and i hope you will be able to help me, im doing my fyp and im short of time, i was able to read voltages perfectly before, when i was not connecting wire to the analogue, the voltage display was 0, then i dont why all of a sudden, when i start the program, the voltage strarts at 2.35 V and has a lot of noise. I tried to format my pc, reinstall new labview, change wire, use another laptop, but same result. In the photo i attached, when i press on the metal part of the arduino where the ports fits, the noise gets reduce. Im doing testing of a stair energy harvester and its very important for me the voltage to be 0 initially. Your help would be really apreciated. Thanks in advance

[akash24]

thanks for the advice, im facing a bigger problem and i hope you will be able to help me, im doing my fyp and im short of time, i was able to read voltages perfectly before, when i was not connecting wire to the analogue, the voltage display was 0, then i dont why all of a sudden, when i start the program, the voltage strarts at 2.35 V and has a lot of noise. I tried to format my pc, reinstall new labview, change wire, use another laptop, but same result. In the photo i attached, when i press on the metal part of the arduino where the ports fits, the noise gets reduce. Im doing testing of a stair energy harvester and its very important for me the voltage to be 0 initially. Your help would be really apreciated. Thanks in advance

[akash24]

I found out a way, i used small capacitor 100micro farad,the reference voltage was then 0V