WLS-9163 and 9211, wrong sample rate?

[mattias@hv]

Hi!

I have a WLS-9163 with a 9211 module mounted. I have connected one thermocouple type K to analog input 0.
I can connect and take measurements wireless. However, I can only achieve 7 S/s without an error message.
I get the following error message when I try to sample 14 S/s in the WLS-9163 configuration.

Error -200081 occurred at DAQ Assistant
Possible Reason(s):
Sample rate exceeds the maximum sample rate for the number of channels specified.
Reduce the sample rate or the number of channels. Increasing the convert rate or reducing the sample delay might also alleviate the problem, if you set either of them.
Number of Channels: 2
Sample Rate: 14.000004
Maximum Sample Rate: 7.142857
Channel Name: _WLS-14049AF-2/_cjtemp

When I use the 9211 in a cDAQ-9172 configuration I can acquire up to 14 S/s from a single channel with no problems at all.

Somehow it thinks that I have selected to take measurements from to channels, which is not the case. 

I Use Labview 8.5.1 with Hardware Drivers from 2009-10 together with Windows XP SP3.

Is this something that you have heard about before?

Best regards,
Mattias

[jyang72211]

Hi,

I think the 14S/s that you are referring to is shared among the 4 channels.  Is it possible that when you used the wireless carrier you initialized 2 channels by accident? 

Yik

[mattias@hv]

Hi Yik,

Thank you for your time. I have check that only one channel is select, and I can only see one channel in the DAQ-assisten.

It seems as if this is not a very common problem.

/Mattias

[MarkGrot]

The NI 9211 is a slow multiplexed module.  It has a maximum sample rate of 14Hz / number of channels.  This is enforced on the ENET/WLS-9162 and USB-9162 chassis.

Timing for slow modules is a little bit different in a Compact DAQ chassis.  CompactDAQ allows you to acquire from multiple modules in the same task.  If the NI 9211 restricted the task to a maximum sample rate of 14Hz/n then other modules would be incompatible with the task.  It would be impossible to have a NI 9237 and NI 9211 in the same task, for example.  Since the cDAQ-9172 only has one analog input timing engine (cDAQ-9174/8 have three) this would severely restrict what modules you could do together.

Instead CompactDAQ chassis allow you to go faster than the maximum rate of slow modules and return updated data as fast as possible.  This means you will see repeated samples.  Try running your NI 9211 at 14Hz with two channels enabled.  Look at your data, you should see that each data point is repeated once at that rate.

[KyleBryson · Accepted solution]

Hi Mattias,

Your task is also reading the CJC on the device once per sample, so you're actually reading two channels.  Reading the CJC (that's the .../_cjtemp in the error message) is necessary to return a temperature value measured from a thermocouple.

Regards,

Kyle

[mattias@hv]

Okey, I see. Thank you very much for all your good answers. I must say that I think this community is extremly professional and a good source for information.

Thank you.

/Mattias