tldr: Can I transmit an analog signal through a noisy environment without it being corrupted, or should I use a digital signal instead?
My requirement is to transmit a signal from a MA3 absolute magnetic encoder 75 feet in the sky to a DAQ module on the ground. This model comes with an analog or digital interface. I would prefer to use the analog, because it is easier to interface with a DAQ module.
With the analog interface, the sensor has 10 bit resolution, 2.6 kSample/s, 0-5V output. To keep linearity of the sensor data around the 0 and 5V boundaries the output load impedance should be greater than 4.7kohms and less than 100pF.
The digital interface uses PWM. It has 10 bits of resolution and has a frequency of approximately 1kHz. The RC oscillator for PWM is only within 10% of its rated pulse period, but this can be accounted for by calculating the ratio of tOn to tOff for each duty cycle. In order to interface this with a DAQ module I would have to use counting logic. I am not a fan of this approach because the counting approach seems error-prone, and it will require learning software for the DAQ. However, I will use it if the analog route is impossible.
For the shape of the signal, I expect it to constantly vibrate slightly from the sensor position changing slightly, but change overall very slowly since the shaft it is monitoring rotates at less than 1 RPM.
There are three complications to this.
- the signal has to pass through a slip ring
- the signal has to travel from a height of 75 feet to the ground - I have heard that long wires act as antennae for EMI and the height of the cable in the sky may affect this
- the wire carrying the signal will be no more than a foot away from wires carrying 3 phases of up to 40V of wild AC
My first question is: based on all of these sources of interference, does the analog signal stand any chance of maintaining integrity when it reaches the DAQ module? I lack the experience with signals to be able to predict whether this is feasible or not.
If you think this is possible, do you have any recommendations for making it work? The only approach I know of is shielding the wire, and keeping it as far away from the power lines as possible.
Thanks for your help