VirtualBench

[x_ca]

I would like to adjust the sampling rate using the NI 4351 for PCI card with TBX-68T and Virtual Bench 2.6. I am logging data to disk every 14 time intervals for four K-type thermocouples (from channel 2 to channel 5) through TBX 68T with Fast Reading and 50 Hz Power line Frequency. According to the formula given on LOGGING DATA AT A SPECIFC RATE WITH VIRTUALBENCH-LOGGER AND NI 435X (link is attached), the seconds between logs should be 30. However, the actual logging rate is 1 time per 60 seconds. I would appreciate it if someone could help me with this issue.

http://digital.ni.com/public.nsf/websearch/720BEF2AFD4383BB862567A60076DC33?OpenDocument

Thanks a lot!

Shawn

[h_baker]

Hi Shawn,

Unless I overlooked something, with your settings there should be 6.36s between logs.  If you want 30 seconds between logs, then your Log to Disk every X intervals number should be 66 (30*8.8/4).  Hopefully this helps!

[x_ca]

Hi h_baker,

Thank you for your reply! The formula for the seconds between logs is:

Seconds between logs = (Number of Channels/Reading Rate)*Log to Disk very X Time Intervals

Where,

Number of Channels = 4+2 =6 (TBX-68T: 2 extra channels) (Refer to the user's guide.)

Reading Rate = 2.8 readings/sec (VirtualBench, PCF=50Hz, Reading Rate=Slow, Multi-Channel) (Refer to Table 3-1 in the guide.)

Log to Disk very X Time Intervals =14

Thus,

Seconds between logs = (6/2.8)*14 = 30 Sec

Could you please let me know why the reading rate is 8.8 readings/sec and the number of channels is 4?

Thank you and best regards,

Shawn

[h_baker]

In your original post, you indicated 4 channels and a fast reading rate (8.8 readings/s).  If your settings are as you indicate in the most recent post, then your calculation is correct.

[h_baker]

Shawn, I see where the two additional channels come from so you are correct with 6.  My apologies on the misunderstanding; however, the reading rate I used was for the fast sampling mode as indicated in the original post. 

[x_ca]

Hi h_baker,

It is my mistake! The reading rate should be slow. If my calculation is correct, the seconds between logs should be 30. However, the actual number is 60 in the log file. When I change the number of channels connect to the terminal block, I get some strange numbers. It seems that the reading rate is not always 2.8 readings per second. Could you please provide me your opinions on that?

Thank you in advance!

Regards,

Shawn

[h_baker]

Shawn,

On what operating system is VirtualBench installed?  I installed the software on my computer to configure the setup and began receiving inconsistent logging behavior.  After additional troubleshooting determined the software was never officially tested on XP.  This is an older software package that was replaced by the release of Signal Express; however, the NI-435x driver is based on the Traditional DAQ driver.  Signal Express only supports the DAQmx driver thus the 435x cannot be used with this software.  

The software must be on Microsoft Windows NT 4.0 or higher, Microsoft Windows 2000, Windows 98, or Windows 95.  If it is on a different operating system, then your logging issues are likely due to incompatibility.  

[x_ca]

Hi h_barker,

Thank you for your reply! The operating system installed on the computer is Windows XP. It seems that VirtualBench is able to take the readings from the PCI card, but it will not log the data at a specific rate. I guess that I have to use LabView instead of VirtualBench to solve the problem. Do you have other suggestions?

Regards,

Shawn

[cyclone2k9 · Accepted solution]

Good morning Shawn,

It appears you are now looking to log temperature using LabVIEW with a 435x device and a terminal block with K-Type thermocouples.  If that is correct, I would recommend using a shipping example with the 435x driver.  You can then find examples in LabVIEW by navigating to Help»Find Examples...»Hardware Input and Output»NI 435x»Measurements.  You will be able to make a temperature measurement with this VI, and then you can choose to log the data to file thereafter.

Best,