Can Daqmx count sinuous periods?

[Derek Lu]

Hi,

I am trying to read my linear encoder by USB-6211. My A and B signals are sinuous signals between +/- 50mV. I want to use the linear encoder task of Daqmx to count the distance I moved, but it doesn't work. Is any requirement for the linear encoder task od Daqmx?

Thanks.

[DjDaveNI]

Hi Derek,

The USB-6211 Multifunction DAQ device is not capable of the Resolver/LVDT measurement you describe. This is because simultaneous sampling and/or a stimulation signal is required (depending on your sensor’s technology Resolver or LVDT). This document does an excellent job explaining the technologies and what types of devices can perform the measurements you desire: “LVDT/RVDT/Resolver Measurements” (http://zone.ni.com/devzone/cda/tut/p/id/3613).

Two hardware options come to mind as a solution for this type of measurement: SCXI instruments or R-Series FPGA instruments. SCXI provides signal conditioning, and FPGA is ideal if you want to develop your own simultaneously sampled encoder reading device.

Can you provide more details about your sensor, like the make/model as well as the manual?

[JoeFriedchicken]

You could also externally condition your +/- 50 mV A and B signals to 0-5 V square waves with some DC offset injection and a comparator. With 0-5 V square waves, you should be able to use the USB-6211's counters to make a linear encoder position measurement.

[Derek Lu]

Is it possible I set a threshold value to build an internal counter? Do you have similar programs?

My sensor is an optical encoder. It generate two sinuous signals within pi/2 phase difference.

Thanks.

[JoeFriedchicken]

I don't quite understand your question. It sounds like you want to use DAQmx to set a compare value for your optical encoder's signals and then use a counter to make the measurement. If that's what you mean, then no, you cannot do that since the hardware does not have that functionality. You will need to externally condition your signals so that they match TTL levels: 0-5 Volts.

[Derek Lu]

I mean since I already got the sinuous signals between +/- 50mV by DAQ. All I want is to count the peak numbes of these signals. So could I set a threshold value to build up a counter by while loop? That will not go through the DAQassistant but write a LabView counter directly.Do you have simular examples?

Thanks.