Hi, I'm a final year engineering student and I'm trying to get a basic DAQ set up on my project rig, A water level & temperature control system.
The system consists of a Siemens PLC (S7-300), HMI, and a number of valves & sensors.
My plan is to use an Arduino UNO and the Adafruit Data logging Shield. Students can then use the SD card in a laptop, and import the data into excel for analysis.
I need to record liquid level, temperature, valve position, heater status, level setpoint and temperature setpoint, and of course a time-stamp for each, so 6 inputs and a time stamp. The system reacts slowly, so a sample rate of 1/s is what I have in mind, I don't want to sample faster than I need to because it's just wasting memory!
My question is regarding the choice of inputs. The rig has analog sensors, a DAC, a PLC, and an ADC, so I have a choice of whether I want to use digital or analog inputs. The PLC takes the digital values from the ADC and scales them to corresponding tank level percentage and temperature in degrees. The level is measure with an absolute pressure sensor, which requires daily calibration, so I'd like to get the DAQ to record the (scaled & Calibrated) digital values the PLC uses rather than taking data straight from the sensors. I have absolutely no experience of Arduinos or Datalogging, and my coding skills are next to none (I'm in the mech stream) but I'm eager to learn about it. Is there any other reasons why I should choose analog over digital or vice versa? If anyone could point me in the direction of any useful reading information/tutorials/etc it would be much appreciated.
The Bottom Line: Is there any reasons to chose digital or analog inputs to log? Does the arduino "prefer" one type over another, or are there any problems i'll tend to encounter with one over the other?