9178 max sample rate lower than expected

[rodrick.pierce]

I'm working with a cdaq9178 chassis that has the following modules: 3x 9229 modules 50kS/s simultaneous rate, 1x 9206 250kS/s aggregate rate, 1x 9213 1200S/s aggregate rate slow module. It is my understanding that the 9213 does not limit the overall speed of the chassis in any way. The 9206 card uses at most 10 channels, so depending on the test we're running our max sample rate should be between 25k - 50k simultaneous samples per second. When I run the test with all 10 channels in use, I get a sample rate that maxes out at 25kS/s aggregate, meaning the simultaneous rate is much lower. Why would this happen? I also have 2 DIO cards in the chassis, but they aren't sampled or timed in anyway, so I don't believe they're involved in any way.

[KatieC]

Rodrick, 

Just to clarify, what test are you doing? Are you only using the 9206 during the test? 

Katie

[rodrick.pierce]

We are using the cdaq to test batteries. There is one thermocouple channel, one 9229 channel, and one differential 9206 channel per battery we connect to our hardware, and we connect up to 10 batteries at once. We also have one additional thermocouple in use for measuring ambient temperature, so at most we have 31 channels all taking samples in a single task.

[KatieC]

Roderick, 

I think there is some confusion on the capabilities of the cards. First off, only the 9229 does simultaneous sampling. So when you say "The 9206 card uses at most 10 channels, so depending on the test we're running our max sample rate should be between 25k - 50k simultaneous samples per second", this is only partially correct. If you are using all 10 channels, then your sampling rate would be 250 kS/s divided by 10 to be 25 kS/s; you would not expect anything higher. However, if you are using 5 channels, then it would be 250 kS/s divided by 5 to be 50 kS/s. Regardless of the number of channels, there is no rate for simultaneous samples as the device does not support this. 

 "When I run the test with all 10 channels in use, I get a sample rate that maxes out at 25kS/s aggregate, meaning the simultaneous rate is much lower." As explained above, we would expect the device to max out at 25kS/s with all 10 channels in use. However, you can't say the simultaneous rate is lower as the card cannot do simultaneous sampling. 

In addition, the sampling frequency of one module does not affect the sampling frequency of another module. The chassis provides a clock for the modules, but it does not set the sampling rate. 

I hope the above sheds some light as to what is going on in your test. 

Katie