Hello. I'm working on a project to monitor the water level in my sump pit using a raspberry pi. I've ordered a submersible transducer sensor, which outputs 4-20ma of current to indicate 0 to 5 meters of water depth. I plan to convert this current into a voltage using a resistor, then read that voltage using an ADS1115 analog-to-digital converter. I have questions about what resistor to use and the resulting voltage range that will be measured.
My pit is only 1M deep. I think it would good to calibrate the resistor/voltage circuit so that I get more "range of motion" in the area I care about. I've read that it's common to use either a
100R resistor - resulting in a voltage range of .4v-2v
250R resistor - resulting in a voltage range of 1v-5v
Since my pit is only 1M deep, that means for a 100R resistor I'd probably only be reading a range of .4v - .7v. It seems like it would be harder to get an accurate measurement of water level when translating from such a small voltage range of (.7-.4)= .3 volts (considering about .3v per meter).
So I am thinking of using something like a 470R resistor, which gives a theoretical voltage range of 1.8 - 9.4v, but since my sensor will never be more than 1M deep, I would get voltages between 1.8 and 3.3. Which leaves me with a range of 1.5v to indicate the depth 0-1 meter.
Does this seem like a good idea? I would of course test the circuit with a voltmeter first to make sure even at full depth it does not exceed 3.3v. Reading the specs on the ADS1115, the absolute max voltage it can handle is vcc+.3. I will be powering it from a 3.3v pin on the raspberry pi.
Thanks for your help.
My pit is only 1M deep. I think it would good to calibrate the resistor/voltage circuit so that I get more "range of motion" in the area I care about. I've read that it's common to use either a
100R resistor - resulting in a voltage range of .4v-2v
250R resistor - resulting in a voltage range of 1v-5v
Since my pit is only 1M deep, that means for a 100R resistor I'd probably only be reading a range of .4v - .7v. It seems like it would be harder to get an accurate measurement of water level when translating from such a small voltage range of (.7-.4)= .3 volts (considering about .3v per meter).
So I am thinking of using something like a 470R resistor, which gives a theoretical voltage range of 1.8 - 9.4v, but since my sensor will never be more than 1M deep, I would get voltages between 1.8 and 3.3. Which leaves me with a range of 1.5v to indicate the depth 0-1 meter.
Does this seem like a good idea? I would of course test the circuit with a voltmeter first to make sure even at full depth it does not exceed 3.3v. Reading the specs on the ADS1115, the absolute max voltage it can handle is vcc+.3. I will be powering it from a 3.3v pin on the raspberry pi.
Thanks for your help.