# Sensitivity of a sensor

I have a current sensor (sensitivity is 22mV/A) which is being used to measure AC current with its time stamp data.

I have connected this sensor to an ADC (12 Bits resolution

Can somebody please let me know whether we can measure an AC sinusoidal current as low as 0.3A with its time stamp data (like input side of a mobile charger from 2-Pin socket), I would be very much appreciative.

• I think that the sensor does not generate any time stamp data, whatever that actually is Dec 10, 2020 at 5:31
• Hi @jsotola. On what basis can we say whether it will generate time stamp data or not? Could you plz let me know as I am naive in this field. If required I can get a different sensor Dec 10, 2020 at 7:24
• the device datasheet would specify if timestamp data is generated by the device Dec 10, 2020 at 7:29

Let's see.

22mV/A * 0.3A = 6.6mV

So your 0.3A RMS AC current will produce a 6.6mV RMS AC voltage at your ADC input. It is a 12-bit ADC. So if the ADC reference is 5V, then the resolution of the ADC is:

5/(2^12-1) which is 5/4095 = 1.22mV

So you will be trying to measure a 6.6mV (rms) signal with a 1.22mV resolution ADC. In practice this will not work super well. The current error, when you include all sources of error, will probably be pretty large. A 0.3A AC current may be detectable, but you will be unable to distinguish between a 0.3A current and a 0.4A current or 0.2A.

Using a lower reference voltage may help. There is another potential problem in that you have to make sure the output of the sensor is in the allowable range of the ADC inputs. If the ADC can measure 0-5V, then you need to make sure the sensor is always between 0 and 5V. If the ADC can only measure 2.5V, then you need to make sure your signal is always under 2.5. Etc.

• Thanks you so much @mkeith for your valuable feedback. As you quoted "So you will be trying to measure a 6.6mV (rms) signal with a 1.22mV resolution ADC. In practice this will not work super well." What is the thumb rule behind this? or rather I want to know, on what basis to i correlate this two parameters. ? Dec 10, 2020 at 7:17
• Well, it is a matter of resolution. Each step of 1 in the ADC is 1.22mV. So if we flip it around 1.22mV / 22mV/A = 55mA per step. That would be the best you could hope for. In reality, ADC's usually have noise in the last step. So you would have a lot of uncertainty in your measurement unless you average over a long time period. Also, I don't know what the reference voltage is. If it is not really 5V, then the analysis changes slightly. Dec 10, 2020 at 7:39
• Thanks a lot @mkeith for your feedback. My ref voltage for ADC is 5V. So as per the calculation, the minimum current resolution that I can measure is 55mA/step ( provided that there is absolutely no niose). Dec 10, 2020 at 9:14