analog input quantized

[julia_S_998]

Hello,

The data input into LabVIEW by my USB-1208LS is precise, but the analog input voltage values are quantized (there are only a few repeating values: 0.696 0.691 0.696 0.701 0.691 0.701 0.691 0.691, etc.). I am measuring the voltages of four photocells powered by the +5V of the USB-1208LS. Each photocell is measured in a different channel using the differental input mode. Is there some way to fix the quantization of the data?

I am not sure if this is a LabVIEW problem, but attached is my block diagram, in case I am not inputting the voltages correctly.

Thank you in advance.

[Dennis_Knutson]

As far as I know, devices from Measurement Computing use the same general design as DAQmx from NI and your use of four separate tasks is just wrong. You should be using a single task that has multiple channels. You aren't getting an error from your code?

[julia_S_998]

Thank you for your quick response!

From what I have found and used, Measurement Computing requires a VI of its own to aquire the data from the each of the channels separately, so right now I have four different tasks, each reading a single channel. I do not get any errors from my code, and it runs fine, other than the strange voltage readings.

[Dennis_Knutson]

We all know that Measurement Computing requires drivers from them. The fact that you posted to the wrong board does not change the fact that you are using their driver incorrectly. Try using s single task with multiple channels and see if your problem doesn't go away.

[johnsold · Accepted solution]

On the +/-10 V input range the resolution of that device is about 5 mV, which is exactly what you are seeing. The resolution is calculated by taking the total voltage span across the range (20 V) and dividing by the number of steps or bins the A/D converter has over that range (2^12 = 4096). So, resolution = 20/4096 = 4.883 mV.

To get better resolution you need to use a smaller range (if your signal wil fit in a smaller range) or obtain a DAQ device with higher resolution, such as a 16-bit or 24-bit converter.

Lynn

[julia_S_998]

Dennis,

I appologize for posting on the wrong board. I am new to this and will be sure to not make that mistake again. I will look into using a single task with multiple channels. If that doesn't work, I will switch to the NI DAQ card to which I am more accustomed.

Lynn,

Thank you for your help. The poor resolution would account for the gaps in the data.