Check IEPE sensor connectivity and IEPE status (PCI 4472)

[Ian_Ren]

Can someone tell me if it is possible to do the following in a LabVIREW program (with PCI 4472, LabVIEW and DAQmx).

1) check the connectivity of an IEPE sensor/cable,i.e., if the cable connecting to an IEPE accelerometer is broken.

2) check the IEPE status of a PCI 4472 channel, i.e, if IEPE of ai0 is turned on. 

Thanks.

Ian

[Ima U]

Hi Ian

When the IEPE is turned on, it remains on until you specifically turn it off. Take a look at this Knowledge Base article for more clarification. I hope this helps.

[preston_johnson]

Here is an application note one might consider in determining whether the cable is broken. 

http://www.imi-sensors.com/technical/trouble.asp

Basically, you monitor the accel with IEPE on and DC coupling and determine if the bias voltage is at the 10V mark with the 4472.  If the bias voltage is at 0 then the cable or sensor has a problem.   

[Ian_Ren]

Hi, Ima

Yes, When the IEPE is turned on, it remains on until you specifically turn it off.

For my application, I need to have some channel IEPE on and some off, and the configuration changes frequenctly.

If I have already turned IEPE on, and on the new task I need to call the DAQmx Create AI Channel (Sub).vi with "Voltage" input, IEPE will be turned off, unless I specify in the property node to set IEPE of desired channels on.   

Ideally, this is what I want to do. If the IEPE was on before I call DAQmx Create AI Channel (Sub).vi, I  will to start measurement straight away; if the IEPE was off before I call DAQmx Create AI Channel (Sub).vi and property node to turn IEPE on, then after commit, I will wait for few seconds to let IEPE sensor to settle.  Therefore, I need to "poll" the device to determine the current IEPE status of individual channels. I guess I can track this from my software, but "polling" may be more reliable.

Is there any way I do this?

Thanks.

Ian

[Ian_Ren]

Hi, Preston

I just did a few tests. The bias voltage is about 24V if the circuit is open (e.g., a broken cable), and the bias voltages for the sensors (Accelerometers, Impact Hammers and Microphones) I tested are between 10V and 14V (about half of the 24V).  Unfortunately, 4472 measures +/-10V only, so it will overload if I use the DC coupling.

Any more suggestions?

Thanks.

Ian 

[Ima U]

Preston's suggestion will work best for you. The overvoltage protection for the NI-4472 is +/- 42.4pk so you will be fine using what Preston suggested. You can have a look at the 447x Specifications if you have anymore concerns. I hope this helps!

[Ian_Ren]

Hi, Ima

While the overvoltage protection for the NI-4472 is +/- 42.4pk, the range is +/-10V only. So it will not tell the difference between 24V (open circuit/broken cable) and 12V (good sensor/cable).

I did figure out a way of checking the IEPE sensor connectivity by using a voltage divider and a second channel (set to DC couple)on the 4472, but it is just not very convenient.

Thanks for your help.

Ian

[Ima U]

Hi Ian,

You are welcome. Could you post a detailed explanation of how you solved the problem? It is a good reference for others.
Thanks!

[Ian_Ren]

HI, Ima

The sketch is attached. Chan1 of 4472 should read 1/10th of the bias voltage, hence within +/-10V range..

Regards

Ian

[Ima U]

Thank you for posting your solution!