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WebDAQ 504 DC Coupled Time Constant


burnsja2

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Good Morning, 

I am using the WebDAQ 504 to log data from an IEPE force sensor.  This sensor has a discharge RC time constant of 100 seconds.  I am concerned with the time constant because I will be collecting some quasi static calibration data and would like a few seconds to be able to do so.  Some power supplies will decrease that time constant.  I didn't see a coupled time constant listed in the data sheet for this logger when DC coupled.  

What is the discharge time constant of the WebDAQ 504 when DC coupled?  

Thank you, 

Josh B

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I am using a Dytran 1053V3 (datasheet attached).  This has a rated time constant of 100 sec.  I have seen some power supplies listed as AC or DC coupled.  From Dytran's literature (attached): "A DC coupled power unit uses a summing op-amp circuit rather than a capacitor to direct couple the sensor to the readout."   

The WebDAQ datasheet lists AC/DC coupling as options, but I am wondering what the limiting discharge time constant would be.  

1053V3_ds.pdf 20170501044839Low_Frequency_Response_and_Quasi_Static_Behvaior_of_LIVM_Sen.pdf

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Hello @burnsja2.

When DC coupling is enabled, there is no discharge at all or, compared to AC coupling, the DTC would essentially tend to infinity. In the given case AC coupling is enabled, the DTC at 0.5Hz would be of 318 miliseconds.

Please let me know if this information is helpful to you.

Regards,

Fausto

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Thanks for answering.  That answers my question. 

Follow up question: Is there a way to enable DC coupling for an IEPE sensor?  I hope to use this sensor during calibration in a quasi-static environment, but I noticed in the documentation / help page > job editor > channels > channel properties: "Note: AC coupling is automatically enabled for IEPE channels."  Is there a way to disable this default and enable DC coupling instead?  If not, I may have to use the voltage mode and provide my own excitation, but I was hoping not to have to do this.  

Josh B

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