I need to connect a sensor system that outputs 0–5 VDC to a data-acquisition system (DAQ) that accepts inputs of ±0.1 VDC (it is designed for a different type of sensor, but I need to repurpose it in this application). (The signals are primarily DC, but there may be AC components. The ranges are the same.) This scenario presents two obvious problems:
The 5 VPP output range of the sensor system needs to be attenuated significantly in order to be compatible with the 0.2 VPP input range of the DAQ.
Naively, I figure this could be achieved with a simple voltage divider, performing a 50-times reduction.
The sensor system has a unipolar voltage output, whereas the DAQ is designed to work with bipolar voltage inputs.
This could be simply ignored, if I were willing to sacrifice the loss of half the DAQ's input range (and thus resolution), but given how much the input signal must be attenuated, I think that is not a reasonable approach.
Therefore, I came up with the idea to use a differential amplifier as a simple way to convert the 0–5 V output of the sensor system to a ±5 V output.
The complete design for the "conversion" circuit is the following:
Note that the sensor system (which generates the input) is modeled here as a waveform generator (far left). It's not actually going to be generating a constant output (in fact, precisely the opposite, or it'd be a terrible sensor), but this is sufficient for simulating the circuit.
According to the CircuitLab simulation, it works, achieving exactly what I want. But I am not an electrical engineer by training, so I'm looking for some expert guidance/review. Is this a reasonable design? Are there any hidden flaws or "gotchas" that I am overlooking?
Is the two-stage design—starting with the differential amplifier to do the unipolar-to-bipolar conversion, followed by the voltage divider to attenuate the bipolar signal to the desired range—correct? Is there a better way of doing this?
Precise and repeatable measurements are important here, to the extent it is reasonably possible. (Obviously, since this is all designed to allow sampling from sensors, the idea is to be able to quantify real-world phenomena as precisely and accurately as possible.) If there's a relatively simple design that would be more precise than this one while achieving equivalent results, then I would be interested in hearing about it. I say "relatively simple" because this is a retrofit/hack. If I have to design a simple PCB that will be inserted as an adapter/converter, then so be it, but both systems (the sensor system and the DAQ) are already existing and can't be easily modified.