Not to mention, you have to compare the precision of the accelerometer to the precision of the cRIO. The DAC on the accelerometer probably outputs either an 8-bit or a 10-bit output. If it’s a 10-bit output, then the values occupy 25% of the precision range of the cRIO, but 9% of the values, for a loss of – well, somebody else can do the math, it’s late. But my point is, if it’s a 10-bit device, you will lose some data.
However, if it’s an 8-bit output, the output precision range is only 1/16 that of the input range, so you have a voltage range that is 9% of the total, but a precision range that is 6.25% of the total. Since 9% is not a clean multiple of 6.25% there will be some error induced by thresholds not lining up, but effectively, you’re not losing any data.
This is all assuming that you’re not getting any EMF on the wire. As far as I’ve seen, there’s a pretty big lack of consistency on analog devices just because of induced interference. If you’re really worried about precision, a more accurate method may be either pulse-width modulation (also imprecise if the timers are not lined up, but on something as fast as the cRIO, that’s not really an issue), or serial data (don’t know which pins can be used as a serial bus other than the I2C port). An example would be these two, from Parallax and SparkFun:
At $35 and $28, these are well within the range of all of the other basic triple-axis accelerometers, and only require one connection to get all three axes, as opposed to connecting three independent analog lines. They can both use either SPI or I2C, so they might be perfect for our setup on the cRIO. Serial accelerometers go all the way down to around $20, but they’re mostly 8-bit resolution at that point.
But as for scaling the voltage coming off of the one you have, you may or may not gain precision. If the accelerometer’s resolution is high enough to warrant boosting the voltage, you have to account for the noise that will be incurred just by virtue of amplification. However, if the accelerometer’s data precision is low enough anyway (8-bit), there’s no reason to scale the voltage, because the V/G (volts per G) precision will not increase with mapping, it’s a resolution problem at that point. If you are going to try scaling the voltage however, do use something with low losses. And don’t worry about expanding into the - voltage range, usually accelerometers only have up to 10-bit resolution (most of the time, if yours is 12-bit, go for it if you can figure out a way), so that results in 1/4 of the cRIO’s ADC resolution. That means if you got the voltage range past 5 volts, that’s the maximum resolution you’re going to get out of the device anyway. I think you’re on the right path using an LM386, they have lots of nice features for this, like both a + and - input for resolution’s sake, and an internal gain. Having all of these features in such a small package guards against interference. And don’t forget the good impact of twisting your wires.