inaccurate readings recorded

[4268]

i am recording a digital signal as an rpm value of a motor rotating but when it records the values in the spreadsheet file the recorded values are lower than the actual rpm values by approximately 500rpm. the recordings are on 1sample on demand in the daq assistant on the block diagram and there is a counter in the program that averages every 5 samples  and the daq assistant will not work unless i leave the recordings as one sample on demand. the data also has to go through a while loop 2 case structures and a stacked sequence structure before being logged to file. is there any way i can get the actual values to be recorded. would recording the values on there own work or how can i get them to be recorded accurately.

[johnsold]

Your architecture sounds unnecessarily complicated.  If you are recording 1 sample on demand, then you are apparently using software timing which typiclaly is not very stable or accurate.

Please post your code including some typical data so we can see what is going on.

Lynn

[4268]

if i select any other mode such as 1 sample hw timed, continuous samples or n samples the daq assistant will not work in the labview program. it gives an error if i select a different mode for the daq assistant to run in. it gives error 200203 saying an external sample clock must be specified for this application. how do i solve this problem

[johnsold]

It is really difficult to tell what is going on from a written description of the program.  Please post your code with typical data for both this question and your filter question.

Lynn

[4268]

i am trying to record an rpm value is there any examples of code that i can look at to fix my code. i want to record the rpm value so that it can be compared to analog signals can it be done with 1 sample on demand or will it not be accurate do i need to use a different acquisition mode

[MikeParkin]

Hi 4268,

I would agree with Lynn in that if you posted your code it would provide us with a better insight into how your code could be fixed.

This will provde a better understanding on what can be done to correct it.