LabVIEW
Connecting an analog input to a digital output
Hi dmarios,
@dmarios24 wrote:
Thank you for the equation. I have a calibration sheet that has a table of load (lbs) and sensitivity (mV/V). Do I still apply the same equation?
Can you attach that sheet?
(A typical force sensor should operate linearly (within its specified tolerances) within its measurement range, so the sensitivity should (almost) be the same for different loads…)
@dmarios24 wrote:
Also, would it be better if I used an analog input of voltage instead of force DAQ for the load cells if i want to create a control loop and use the same units (Volts) for everything?
Why do you want to use "same units for everything"? Why not measure force (N) and apply voltage to your output? The controller in between (like a PID controller) can convert units between process and output values…
I am attaching the datasheet.
I read in some forums that the PID controller need to have the same units for the setpoint, the process variable and the output. Is this not correct?
Thank you.
Hi dmarios,
@dmarios24 wrote:
I read in some forums that the PID controller need to have the same units for the setpoint, the process variable and the output. Is this not correct?
No, that is not correct.
I used PIDs to control pv=massflow [l/s] using output pump speed [rpm]. Or to control temperature [°C] using heater duty cycle [%]. It's all placed into the PID gains…
In addition to the previous message:
Voltage (V) = Load (N) * Sensitivity (mV/V or µV/V per N)I would use the formula:
Voltage (mV) = Load (N) * Sensitivity (mV/V per N) * Excitation [V]This way the units match…
Now the calibration sheet makes sense: 250lbs * 0.0088mV/V/1lbs * 4.99V = 10.978 mV.
(The calibration sheets I used so far always also provided linearization factors…)
