03-08-2012 04:23 AM
Hi!
I connected voltage pressure transducers on a machine using DAQ Assistant. Sensors used are TP12 - 500Bar. I used linearisation to figure out slope(31250) and Y-intercept(-125). The problem I am having is, that sensors are creating too much noise. The numbers are jumping from -2 bar to 3 bar, whis is way too much, cos I need 1% accuracy. Is this something normal getting this numbers, or have I done something wrong?
Thanks for help!
Jure
03-08-2012 04:26 AM
there varying by 1% which is your spec.
I assume you have checked your hardware and connections.
What are they measuring? is it at a constant pressure?
03-08-2012 04:34 AM
Thanks for quick answer. On the datasheet of transducers the accuracy shoud be 0,2% (Linearity&Hysteresis). The hardware should be ok, so shoud connections. Yes, at constant pressure the number is jumping up and down by 5 bars. If I put 2 transducers (exactly the same) on the same pressure line, they shoud measure the same pressure, but are giving 2 or 3 bar difference.
03-08-2012 04:38 AM
worth checking connections, wouldnt be the first time Ive had similar faults from a dodgy lead. What is the Daq hardware your connecting it too? also can you measure the raw signal from the transducer and check that is stable. Hopefully you can prove beyond doubt the hardware is working fine. After that we can look at the DAQ device and software.
03-08-2012 04:44 AM
03-08-2012 04:56 AM
I dont know the specifics of your devices but the transducers I have used in the past, some are powered from a dc source and have a output wire pair giving a voltage or current. This will be specified as for example 0-10V with a sensitivity of 100mv/bar. range of 100Bar.
The reason the sensitivity comes into it , if we follow my example through but change the fsd to 500bar. the sensitivity becomes 20mv/bar. Your signal is varying by around 100mv. Depending on the resolution of the DAQ it may be an error introduced when it is sampled, as there are only a finite number of values it can read. causing what appears to be a measurement error. Do you know the accuracy of the DAQ for example 16bit or 13 bit? if its 16bit then you have 65536 discrete values. accross the full range of the daq. The cards I have used typically have a range of -10 to + 10V. giving a a step size of 0.3mv which should be fine. If its 13bit then it becomes 2.4mv.
sorry for the quick overview. Could you post the vi for us to take a look at and maybe make some suggestions?
03-08-2012 04:57 AM
just read the spec on the daq your using should be more than good enough
03-08-2012 05:01 AM
just finished reading the specs, you are using a analogue current input module with a voltage transducer? could you confirm this and if there is any signal conditioning in the way
03-08-2012 05:01 AM
Have attached just sensoric part of a program since whole program is quite large(Can also post it if you like).
03-08-2012 05:05 AM
I have 2 voltage pressure transducers (using NI9201), and one current pressure transducer (using NI9203).
Voltage transducers are 0-10 V, 0-500 bar
Current tranducers are 4mA-20mA, 0-500 bar