DAQ interfacing, what is the best way to measure the data ?

[hamadeh]

Hi ,

I have a 16 bit DAQ connected to a PC using the USB port, NI LabVIEW driver for this DAQ is available, I want to connect a pressure transducer to this DAQ to measure some pressure value between the lips, what I want to ask is the following:
What is the best method to measure the pressure value from the transducer ? , is it to get the maximum obtained value from the DAQ or something else ?

Thanks in Advance.

 

[IanP]

Re: DAQ interfacing, what is the best way to measure the dat

1. Resolution:
In your case you have 16bits what gives you 65536 steps.
2. Input ranges:
Again, in your cas you hav Nationa Instruments DAQ card, so it is quite possible that you will be able to select the following input ranges: 0V to 5V, -5V to +5V, 0V to 10V and -10V to +10V.
3. Pressure transducer: it is very common that they are of 4-20mA devices.
Now, you have to select termination resistor. Very common value will be 250Ω and that operates in the ronge of 1Vdc (at 4mA) to 5Vdc (at 20mA).

So normal selection of the possible input ranges will be 0V - 10V.
However, if instead of 250Ω you select 220Ω you can select 0V - 5V with resolution close to 67µ (5V/65536).
Also, be aware that the lowest voltage will not be 0V but 1V@250Ω or 0.88@220Ω.

For normal situation you will be more tyhan happy having pressure resolution of 0.1bar for a pressure transducer 0-100bar or even 0-10bar so you will drop some low bits from available 16.

The main criterion is always resolution you are happy with..