Brüel&Kjaer Type 4393 V accelerometer sensitivity

[Saad@cbe]

Hi ,

I recently installed NI Signal Express with Sound & Vibration Toolkit, while configuring the sensitivity of the B&K accelerometer 4393 V, I find the sensitivity is defined on NI Signal Express with V/g but it's definitely on the B&K accelerometer with pC/g (cf. The attached fig).

Until now I didn't find any conversion possible to input the correct value of the sensitivity in NI Signal Express.

Hoping to find some help from you, I'll be so thankful.

Regards 

A.S.B

[Saad@cbe · Accepted solution]

Ok  , I spent the whole day trying to find the solution of this ''imaginary'' problem.

According to  Brüel& Kjaer , I need a physical converter ( Type 2647 ) to have a 1 Volt for 1 pC but this converter needs a feeding on ICP by the DAQ.

But according to NI , the NI 9234 DAQ has to ability to convert the pC automatically to V without any need to the physical converter and it feeds the accelerometer by ICP.

To summarize, just put the accelerometer in BCN connection and make your acquisition.

Done.

ASB

[Logan_K]

I took a quick look at your accelerometer, and I a pretty sure that the information you got from B&K is correct, and you are going to need that Charger Converter in order to properly measure the accelerometer with the 9234. Here is some reference material for you... I recommend jumping down to the "Charge Mode Accelerometers" paragraph, which I believe describes the accelerometer that you are using.

http://www.pcb.com/techsupport/tech_accel.aspx#.Up4peMSfiKs

Cheers!
Logan

[Saad@cbe]

Thanks Logan ,

But according to NI Technician, there's no need to charge converter. The QDAC do the conversion because it feed the sensor with ICP.

I tested it and it gives me the same data  as with the B&K charge converter.

Thanks again.

[Henrik_Volkers]

Your sensor is a charge source with XX pC/ms²

Together with it's capacitance (and more worse: the cable capacity and the input impedance) a charge convert to a voltage U=Q/C. That voltage is what you measure with your DAQ card.

Even more annoing is the effect of cable microphonie : Move the cable and it's capactance will change, so will the measured voltage.

Believe me, if you want to make reasonable measurements with this sensor you will absolutely need a charge amplifier to get a voltage

or (if your DAQ supports IEPE) a charge to IEPE conditioner.

Here I build a tube based one, but building a stable good charge amplifier is an art. 😉

[Henrik_Volkers]

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Saad@cbe wrote:

But according to NI , the NI 9234 DAQ has to ability to convert the pC automatically to V without any need to the physical converter and it feeds the accelerometer by ICP.

ASB

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Wrong: The 9234 supports ICP (=IEPE) accelerometers. ICP accelerometers have a charge to voltage converter already build in.

But you don't have a ICP sensor.

[Saad@cbe]

I have already the converter ...so even if the 9234 don't work, as NI said, The output to my DAQ is in Volt.

Regards

[Suglob_Artur]

I've got B&K Deltatron (IEPE???) 4396 and 4519 Sensors. They have pre-installed charge converter 2646. Data sheet says that it must have 2...20 mA constant current supply. If I use NI 9234, I'll have IEPE excitation current 2,0...2,1 mA. Is it the currrent that I need for correct work of the sensor? If I understood correctly, I could work with 9234 direct, right?

Thanks for help,

Best regards

[Henrik_Volkers]

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@Suglob_Artur wrote:

I've got B&K Deltatron (IEPE???) 4396 and 4519 Sensors. They have pre-installed charge converter 2646. Data sheet says that it must have 2...20 mA constant current supply. If I use NI 9234, I'll have IEPE excitation current 2,0...2,1 mA. Is it the currrent that I need for correct work of the sensor? If I understood correctly, I could work with 9234 direct, right?

Thanks for help,

Best regards

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Yes, sound reasonable so far.

Deltatron, ICP,( forgot the Kistler naming 😉 )  with minor differences all are IEPE or CCLD ...   so again_ Yes 🙂