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DAQ selection for plethysmograph/metabolic setup

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I hope that I am in the right place – please redirect me if not.  

 

I am trying to build a small animal plethysmograph from spare parts that I have been able to procure from various labs. This is to be “a learn as you go” experience for both the hardware and writing software (Labview and Matlab). I am completely new to this with no engineering background, so sorry if these are very basic inquires. I have assembled the following components, but now, the most critical component is the DAQ. I am hoping that people here can point me in the right direction for choosing a good PCI DAQ or other NI system for signal conditioning, if needed, and data acquisition.

 

Equipment:

 

Setra 239 pressure transducer – output voltage +/- 2.5V

(might be supplanted by a Validyne DP45 – output voltage  24mV – Would I need an amplifier then?)

 

Ametek Oxygen Analyzer S-3A/I

Output voltage 0-5V

 

Ametek Carbon Dioxide Analyzer Model CD 3-A/I

Output voltage 0 to 7.5V

 

Still to be acquired:

Animal chamber temp measurement system  - (thermocouple ?)

 

Telemetry heart rate monitor (Home made from: A low-cost telemetry system suitable for measuring mouse biopotentials - Lin et al. 2007)

 

I have been considering purchasing the PCI-6024E (used in the above paper) since it seems to have the ranges that I need for voltage and enough inputs for everything. Do higher end DAQs with signal conditioning offer analog conditioning similar to the SCXI chassis and components? Do I even need any sort of signal conditioning with this equipment? I believe all signals are linear, at least for the analyzers and transducers, but if not, would that be addressed by the software or is that a DAQ consideration as well?

 

Thanks for any help that can be offered as I stumble through this.

 

Best,

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Accepted by topic author Just_Starting

Hello Just_Starting,

 

The 6024E is an older board that uses older (i.e. more difficult to find and thus expensive) components.  The PCI 6220 or PCIe 6320 (depending on if you need a PCI or PCI Express DAQ device) are replacements that would give you similar performance at about $400 cheaper (as long as you don't need to run any existing code that was written in the Traditional DAQ driver).

 

Whether or not these boards are suitable for your application is going to depend on your accuracy requirements.  Of the three boards mentioned, the 6320 has the best accuracy for voltage signals across all ranges.  Usually the biggest concern would be the small voltage signals (24 mV or the thermocouple channels).  When using the ±200 mV input range, the accuracy of the 6320 is specced at ±72 uV under conditions described in the Detailed Specifications.

 

 

So, if you can tolerate an accuracy of ±72 uV on a 24 mV input signal then you shouldn't need any external amplification if you are using the 6320.  You can measure the higher voltage channels using the ±10 V range of the 6320 for an accuracy of ±2.26 mV (it is not a problem to configure independent channels to use different voltage ranges on our current DAQ devices).

 

 

Thermocouples are just one option to measure temperature--they are typically used when a low-cost or large-temperature range solution is necessary.  Here is an external link showing the accuracy of thermocouples across their ranges, you might want to verify that this would be suitable for your temperature measurements.  If not, there are likely other options but these may require some signal conditioning (current excitation etc.).

 

 

You may create custom scales in software for each input channel to convert voltage back into the quantity being measured (these can be linear or higher-order).

 

 

You will need a terminal block with the 6320 or 6220--I would suggest the SCB-68 if you do not need conditioning.  If you do decide to use conditioning (i.e. RTDs instead of Thermocouples, additional amplification on low voltage channels to improve accuracy, hardware filtering to remove noise) then you could look at the SCC-68 in combination with the desired SCC modules.  SCXI or CompactDAQ platforms are typically more suitable for higher channel count applications.

 

 

I hope this helps, if you have any questions don't hesitate to ask!

 


Best Regards,

John Passiak
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It's been a while, but your suggestion have worked great. Now I am fumbling my way through the software!

 

Thanks,

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