I've got water pressure transducer which outputs -15mV to 115mV and I need to use op-amp to scale this to 0-5V for arduino ADC. What kind of circuit and op-amp is needed when range starts form negative millivolts?
Also I'd like to "simulate" zero pressure (around 5mV) and good pressure (around 80mV), but I don't find any voltage regulator to these ranges? Voltage itself is not that critical but it should be stable, is voltage divider enough?
Thanks for all replies!
How is the device creating this -15 mV ? What sort of power input does it have ?
I would start with the simplest possible non-inverting opamp circuit with a gain of maybe 20. It is not compulsory to make the full-scale output equal to 5V, and it is more complicated to do so.
If you get an opamp with a power supply of 5V and zero, you won't get a negative output. Unless the negative cases are important to you, I would just ignore them and treat them as zero.
If you want to test this without more circuits, you can set the analog reference voltage on the arduino to 1.1 volts.
You can directly connect your device, and you will get between 0 and 100 analog counts for an input of 0 to 115 mV. This may be enough resolution for your requirements, at least to test your logic, and that the device is doing something.
I don’t know if an input of -15 mV will damage your arduino, but I rather doubt that it will. You would just get an analog reading of zero. There would be a specification somewhere for the input tolerance, someone will know what it is.
10VDC input for excitation, guess it has some active electronics inside?
I don´t know about this -15mV either, when I get a loose sensor I will try it in bench. In the current setup it outputs 5mV when pump not running, so that's 0 pressure for me and 70 to 85mV when pump running. These are the figures for now. So at the moment 0mV to 115mV is fine and this to 0-100 steps are good enough.
But later on I need to respond to the specs, so I'm interested to be able to see -15mV as well, maybe indicating faulty sensor? I can get -+5V or whatever to op-amp if needed. Maybe later I have datasheet for the sensor.
How would you create 5mV and 80mV for simulation?
Two resistors or a resistor and a potentiometer.