Which DAQ for temperature and force

[picante]

Thanks for your reply and apologies about the delay.

Would I need to get an X series NI device to measure frequency then?

I know so many questions, also could you please let me know how the "calibration" process works around making the DAQ or software know that a specific frequency means a specific flow rate. Is this normally a trial and error process, should I expect for the vendor of the sensor to provide more technical info?

Thanks again.

[Henrik_Volkers]

Well. you migth use the 6008 as an event counter. This would give you the total pulses (volume). If you read the counter (software timed) and take the difference you can calculate the flow rate. Would need a closer look at the accuracy you need for this.

As I understand your needs, it's a proof of concept.

For industrial use you would choose industrial grade temperature sensors (easy replaceable, robust design, ...), as less money as more McGyver is needed 😉

A X series card provide much more possibilities, at a higher price

[johnsold]

Certainly an X series device would make it easier to measure the frequency.

Calibration: It sounds like you are talking about scaling first, and then, possibly, calibration.  Scaling is the process of taking a measurement in one set of units and performing a mathematical operation on the data to get a result in the units of the physical system.  Here you want to change a frequency to a flow rate.  The manufacturer of the sensor will provide at least a nominal scale factor, such as 1 milliliter per pulse.  For such a simple sensor the formula would be flow (ml/s) = 1*frequency (Hz).  More complicated systems might require y = m*x+b lineare scaling or the complicated logarithimic equation relating a thermistor resistance to temperature.

The manufacturer should also provide an indication of how accurate the sensor is.  This might be expressed as  1 ml/pulse +/-10%.  If this is not close enough for your work or if the value drifts over time, then calibration will be required. To calibrate you record the output of the sensor while measuring the flow by some other means of known accuracy. For example you might capture the flow in a graduated cylinder known to be accurate to 100 microliters over a time period of 100 seconds with the time known to within 1 second. Then you can calibrate the scale factor to within about 2%, although error propagation is not necessarily quite that straight forward.

My guess is that all you need now is scaling.

Lynn

[picante]

Thank you both, you have been great help.