PCB Vibration sensor readings

[osmosis]

Good day all,

Kindly assist on this. I have a PCI 6221 and a connector block BNC 2110. I am using a PCB accelerometer to acquire signal from a modeled building with the aim of getting the frequency components  from the time response after exciting the building at a specific constant frequency. The problem is I kept noticing that I cannot select acceleration with PCI 6221 so I selected voltage in DAQ. The time response seems okay but the FFT is totally not worth it. I presume I should get my specific frequency back since this if forced excitation but this is not happening.

My question are

1) Since PCB accelerometer are supposed to be given a little voltage of 4A to get them started, can I use PCI-6221 the way I am using it and still acquired signal from my building which can be presumed normal.(I mean okay)

2) Is it right for me to select voltage in DAQ instead of accelerometer using PCB accelerometer when the aim is to acquire acceleration values or let me put it this way :if I cannot get a card that can read acceleration can I still used the voltage in DAQ since the PCB ICP accelerometer gives out voltage values. Please which is the right way.

[Ian_Ren]

PCB ICP sensor needs a constant current supply, which PCB called "ICP" and NI "IEPE" (https://www.ni.com/en/shop/data-acquisition/sensor-fundamentals/measuring-vibration-with-acceleromet...

To power your PCB accelerometer,  you need a card with IEPE or have to use an external conditioner.

To perform frequency analysis later, you need to use an antialiasing filter before A/D conversion.

If the phase between channels is important, you have to have simultaneous sampling.

I suggest you take a look at the Dynamic Data Acquisition (DSA) cards NI provides 

[Henrik_Volkers · Accepted solution]

What sensor type? Datasheet?

As already noted you probably  need a 4mA exitation current to run the sensor  and a decoupling capacitor

A 4.5mA  current limiting diode is for example the CCL4500  see http://www.centralsemi.com/PDFs/products/CCL0035_V2.PDF

(and they have a request sample button 😉 and the 3.5mA type will work too  )  and two 9V blocks or a 18V Voltage source

The decoupling capacitor should be a 470nF (or higher) foil capacitor

How to put it together is noted here

http://www.pcb.com/techsupport/tech_signal.php

Like this you can use your 6221

Or you can buy a signal conditioning box from PCB (or B&K, or Kistler, or ...) or the noted ICP (IEPE) card from NI

[osmosis]

Thanks a lot Henrick.

Really grateful for your response. For the sensor type. I am using an ICP accelerometer with model number 603C01.

Please is it save to admit that clicking on the icon Voltage while acquiring the signal in DAQ is wrong and will not give the required accelerometer reading.

Also if I can change the card, then should I change to acceleration in acquire signal tab in DAQ or used voltage?

Thanks to you all for your response.

[Henrik_Volkers]

With a 6221 you can't read a ICP(IEPE) sensor directly.The sensor need a constant exitation current between 2mA and 20mA to provide a voltage output of XXXmV/ms² plus an offset of about 10V.

Solutions:

Use a signalconditioner like

http://www.pcb.com/spec_sheet.asp?model=482A21&item_id=12217

or

http://www.pcb.com/spec_sheet.asp?model=480C02&item_id=12061

the boxes will supply the sensor with appropriate power and have a AC signal output that fit to your 6221 (Basically the same circuit I noted above, with housing , connectors and power indicators etc)

or switch to a NI Card that can be used directly with such type of sensor (IEPE) like the USB-4431

Depending on your measuring task there might be other cards from NI that better fits your needs, just give them a call ...

[Lord_Kian]

Hi i have a question is posible use a USB 6259 DAQ with the custom voltage excitation input type to provide a excitationfrom of 5V to a 608A11 accelerometer sensor, i don-t gone use all the range of the sensor is probable that only need -/+ 10g.

[Henrik_Volkers]

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@Lord_Kian wrote:

Hi i have a question is posible use a USB 6259 DAQ with the custom voltage excitation input type to provide a excitationfrom of 5V to a 608A11 accelerometer sensor, i don-t gone use all the range of the sensor is probable that only need -/+ 10g.

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No, the sensor will need at least a 2mA current source going up to at least 18V (according to the spec, probably 15V will do also with reduced range , 10V for the biased output plus signal(2V) plus 3V headroom for the current limiter , bias  can be 10V+-1V))

You will always need a CURRENT source (eg. a current limiting diode or other circuit) .

A crude way maybe working would be using a current limiting diode and two analog outputs, one -10V ,one +10V (analog out should be able to source and sink 2mA)  BUT the housing of the sensor usually is conncted to GND and the the shielding ..... no good idea for a serious measurement.