Can I use NI-USB-6251 to directly measure signal from IEPE accelerometer?

[Robert MacDonald]

I have an NI-USB-6251? I want to measure the signal from an IEPE accelerometer (PCB Piezotronics PN 352A25). I want to know if I need a signal conditioner or if I can measure the output directly with the analog input to the NI DAQ?

[Hillman]

 Hi Robert,

Thanks for the post and I hope your well today.

The accelerometer outputs between 18 to 30 VDC, 2 to 20 mA and 20,000 Hz max. ( i think)

The USB 6251

Maximum working voltage for analog inputs (signal + common mode) ................ ±11 V of AI GND

Input range ...................................... ±10 V, ±5 V, ±2 V, ±1 V, ±0.5 V, ±0.2 V, ±0.1 V

Sampling rate Maximum 1.25 MS/s single channel, 1.00 MS/s multi-channel (aggregate)

So the max voltage is 10V (say) so you would need to be stepped down. As for the sample rate you should be fine. With transducers its always a good idea to check currents and impedences, but they seem fairly matched.

For your reference please find:

NI 625x Specifications

http://www.ni.com/pdf/manuals/371291h.pdf

This has more data regarding the inputs (and outputs). This should help you to make an informed decision. Please let me know if you have any questions.

Hope this helps, 

[Seth_B.]

Robert,

Just to clarify, is this the accelerometer that you are planning to use?  If so, the input range for the sensor can be calculated by multiplying the sensitivity by the range (2.5mV/g * ±2000g) resulting in a ±5V range.  Thus, you can use the ±5V range for your USB-6251 with this accelerometer.  If you select the ±5V range using the DAQmx driver, DAQmx will set the gain automatically for you, allowing you to take advantage of the full resolution of your card over ±5V.

However, you will need to provide external excitation.  That accelerometer requires a constant current excitation between 2-20 mA at 18-30 VDC.  Our M-series cards cannot provide excitation.  Instead, you should look into purchasing an excitation source from either PCB or another supplier.

Message Edited by Seth B. on 12-16-2008 09:20 AM

Message Edited by Seth B. on 12-16-2008 09:20 AM

[Hillman]

Hi Rob,

I would like to confirm my post I was unsure (as I stated) what the range was.. I happen to agree with Seth. I got confused between the excitation voltage and input range. I didn't think my take on the datasheet made sense ...sorry about that. 

[Robert MacDonald]

Thanks for your input. You are correct. I needed to purchase a signal conditioner to excite the sensor.

[preston_johnson]

You might consider the following additions to your USB-6251, if you have the mass termination option.

This connector block that holds signal conditioning modules

https://www.ni.com/en-us/support/model.scc-68.html

This signal conditioner:

https://www.ni.com/en-us/support/model.scc-icp.html

Let us know if this helps

[yogi_patel]

I am in the same boat as Robert in that I have a NI PCI 6251, NI SCB 68 and PCB 352C03.  I know that you need a signal conditioner to provide a constant current source to have the accelerometer work, but I was wondering if the NI SCB 68 can provide the current that is necessary to run the accelerometer.  If not, what would be the best addition to my current setup that will allow me to use my ICP accelerometer.  My accelerometer has an input range of +/- 5 volts, so it should be fine with the DAQ.

[ie.aleja]

Hello Yogi,

the NI SCB 68 is just an extension, this wont let you provide the excitation to your sensor, because you need from 18 to 30 VDC as an excitation voltage of your sensor and a constant current from 2 to 20 mA, the PCI 6251 cannot provide this voltage or current, so you would need an external excitation source for your sensor.

Best regards,

[yogi_patel]

Hi Miriam,

Would I be able to use an MEAS Model 161 or MEAS IB-ACH-01 to excite the accelerometer and work with our current setup or a NI Elvis II+ unit?

Sincerely

Yogi Patel

[ie.aleja]

Hello Yogi, 

This device cannot be used to excite your sensor, because still is not providing enough voltage and current. But with the ELVIS II+ unit you could provide the external excitation, you would need to make sure the references are set up correctly that way you can have 30V and they can offer up to 500 mA.

I hope this works.