cDAQ 9184 with NI9232 module for accelerometer and pressure sensor

[wisjaf12]

I am trying to build a CompactDAQ system to measure two signals: vibration and pressure in pipeline system. The system will consist of the following: cDAQ9184 chassis, NI 9232 Module. IEPE accelerometer  to measure acceleration (vibration) and pressure sensor for pressure measurement. My question is: Can I connect the pressure sensor into the NI 9232 module? I found in NI website that this module is designed for acceleration and supports signal conditioning and excitation for accelerometers but nothing mentioned about pressure sensors. On the other hand the website mentions NI9237 module as the best choice for pressure sensors. So can I just use NI 9232 for both sensors or not.  Thanks

[RavensFan]

What is the pressure sensor you are using?  Is it based on strain gages or does it have a voltage or current output?

[Jason-M]

wisjaf12,

You are able to set up the 9232 to measure a regular pseudodifferential voltage input between 30 V and -30 V. You will not be able to measure a current or bridge based signal on this device. Keep in mind that the 9232 is a DSA board, so it will over-sample your signal and spit out an average, so you may see some unexpected measurements. Also, these boards are not very good at measuring DC signals or very low frequency signals, so accuracy would be compromised. Since, however, you mention an interest in the 9237 board; I assume that you are using a bridge-based sensor. If this is the case, as stated before, you will be unable to measure this signal with this device. We definitely recommend the 9237 for this type of measurement.

Best,

[wisjaf12]

RavensFan,

I didnt order the pressure sensor yet, but it definitely will be strain gage besed bridge type sensor.

[wisjaf12]

Jason-M,

Does that mean that I will not be able to conect a bridge based sensor to NI9232 even if I provide external excitation for the sensor by using 12V battery? I mean, is there any way to use the NI 9232 for the accelerometer and the bridge pressure sensor (with external excitation for the bridge) rather than purchasing additional module (NI9237) ?

[preston_johnson]

The 9232 provides IEPE excitation for sensors.  This is a different voltage (24V) than used by strain gauges / bridge sensors (10V or 12V). 

If you provide external power to your pressure bridge sensor, the 9232 will do an excellent job digitizing the voltage(s) across the bridge.  So, yes, you can consider the 9232 as a voltage input where the dynamic > 0.1Hz portion of the signal is best measured by DSA devices. 

[wisjaf12]

Preston-Johnson

Thank you for your reply. But Jason-M mentioned that the DSA of the NI9232 will oversample the bridge signal affecting the accuracy. So, What do you see?

[preston_johnson]

All delta sigma ADCs use an oversampling technique with digital downsampling and anti-aliasing filters.  This is true of all the NI C series modules (9232, 9237, 9235, 9236, etc).  The effective sampling rate is typically around 1000 samples per second on the lower end. 

With the 9232, dynamic pressure (AC signal) is best measured although you will get decent DC accuracy. 

What pressure transducers are you considering?

[wisjaf12]

Preston-Johnson

I didn't purchase neither the pressure transducer nor the accelerometer yet. And that is for two reasons:

1- I wanted to make sure that I could connect both sensors (accelerometer and bridge transducer) into NI 9232 without any problem.

2- I am not familiar with sensor, So I am doing my best to find the right sensors for my application and also to find good suppliers with reasonable proces since I am a grad student with no actual fund. But now that I know (according to your reply) I can use the NI9232 with the accelerometer and the pressure bridge sensor I will start looking for suppliers for the sensors.

So your question leads me to another two questions:

1- Do you know any sensor suppliers with affordable prices?

2- Based on what factors/variables should I choose the accelerometer and the pressure sensor?

[preston_johnson · Accepted solution]

Here is an IEPE (ICP(r)) source of pressure transducors: http://www.pcb.com/products/browse_productlist.asp

Kistler is another vendor.

To help choose - can you tell us more about what you will connect the sensors to - what is the unit under test?

What are you hoping to discover or monitoring from the unit?