Connecting Kistler 6215 to NI cRIO

[FarukMW]

Hello, I am trying to connect Kistler pressure sensor 6215 to LabView and NI cRIO.

The main concern is that this is not IEPE sensor, and requires additional charge amplifier according to Kistler's manual.

Is it ok to connect it directly to NI9234 without any additional electronics between ?

Thank you in advance,

[nar5112]

You will most likely need a charge amplifier, either in-line or a separate unit. I believe this particular sensor does not have the built-in amplifier circuits found in IEPE type sensors. I can't confirm this though because I can't find documentation on this particular sensor. The in-line charge amplifier (something like a Kistler Type 5050B) convert the high impedance signals charge signals to low impedance voltage signals. These charge converters are basically the IEPE amplification circuits, and therefore require the IEPE current source (the 2mA for the NI9234 should be enough). 

[Henrik_Volkers]

If you have a IEPE reading unit,  the inline charge to IEPE amplifier would be the best solution. Kistler, B&K, PCB , MMF (metra)   they all make so many, that they sell them 😄

[FarukMW]

Hello nar5112, thank you for reply. Here is the documentation for the Kistler 6215. (http://www.helmar.com.pl/helmar/plik/6215_nn3885.pdf). You are right for the non existing IEPE circuit in sensor. That is my main concern, because NI says in manuals for NI-9234, that it can be used for IEPE and non-IEPE sensors. Tricky thing is what they mean by non-IEPE ? . On the other hand, KISTLER is using following terminology: IEPE and PE sensor type. For PE sensor types, they developed NI cRIO compatible module (https://www.kistler.com/ar/en/products/components/signal-conditioning/charge-amplifier-module-ki-517...). What I understood that this module have built-in charge amplifier. I would like to use this, but my application requires 125 kHz sampling. I think that I can solve data sampling easily with NI, but can not find the appropriate charge amplifier (that will cover this frequency range) until now. 

[nar5112]

All they mean by IEPE and non-IEPE is whether the sensor needs a constant current source. An IEPE sensor needs at least 2mA current in order to operate correctly. Essentially they are saying you can "toggle" the IEPE current source according to your needs. When Kistler says PE, they are referring to a charge mode sensor (I.e. high impedance charge based signals). This means the output of the sensor is in C rather than typical V. The cMod made by Kistler looks like it will internally convert the charge to a voltage. You can make the NI system work if you purchase an inline charge amp. However, the NI module only samples out to 51.2 KHz, so you are still not hitting your frequency spec.

[FarukMW]

There are the NI modules that can fit my needs. i.e. NI 9232 (or even some X series USB cards), but my problem is that charge amplifiers are mostly working up to 50 kHz frequency range, and still can not find suitable one for my application (125 kHz).

[Henrik_Volkers · Accepted solution]

Well, a lot of charge amplifier (CA)  are only specified up to 100kHz 🙂 and most of the labs will only use and calibrate them up to 20kHz, but you can ask TMS(PCB) , Bruel&Kjaer, Kistler, MMF for CAs or inline amplifier up to 150kHz.

That`s what the application engineers are for 😄

The preamp stage of my  BK2525 CA is good  >200kHz, the BK2635 is good up to ~130kHz (peaking at 140kHz)  but you should keep the cables short , and run the IEPE inline amps with a higher current (10-20mA) ...

[nar5112]

I think you are confusing IEPE devices and charge devices. The 9232 is another IEPE device. It does have a higher sampling frequency, but it is still only IEPE. You would need an IEPE sensor, or the in-line charge amplifiers that use the IEPE source. You could purchase a bench-top charge amplifier also. It offers a little more flexibility, at a higher expense. These amplifiers do not require IEPE since their power comes from the wall. The other issue is that most charge sensors, and the amplifiers, are limited to 100kHz due to the capacitance acting as low pass filter. With these amplifiers you can still pass the high frequency signal through it, but expect attenuation (maybe -3dB depending on the amplifier). I would recommend checking www.pcb.com for amplifiers, and maybe more information on building a charge amp measurement system.