Low pass filter

Helmut O'Brian

Posted on 06.06.2017 09:10

Hello Slovenia,

Just a little question about the Low Pass Filter options in DEWESoft (SIRIUS STGv2 hardware).

We have those options for the Low Pass Filter :

  • OFF* (HW: 100 kHz)
  • Alias free* (HW: 100 kHz)
  • 30 kHz* (HW: 100 kHz)
  • 10 kHz* (HW: 100 kHz)
  • 3 kHz* (HW: 100 kHz)
  • 1 kHz* (HW: 100 kHz)
  • 300 Hz* (HW: 100 kHz)
  • 100 Hz* (HW: 100 kHz)
  • 30 Hz* (HW: 100 kHz)
  • 10 Hz* (HW: 100 kHz)

What is the value of the frequency in "Alias free" frequency option ? Also, what does "HW : 100 kHz" mean ? Is it an hardware filter on the board ?

Do you have some link I can use to find informations like it instead of annoying you ?

Have a nice day.


DEWESoft Support
Technical support
Posted on 06.06.2017 11:16

Hello France :),

there are two types of filters in DEWESoft: Analog (hardware) and digital (software) filters.

A hardware filter is always running in the background and will be set at 100 kHz unless your sample rate goes below 2 kHz, at which point the filter will switch to 5 kHz. The digital filter that's currently chosen by default is Alias free (also called Anti-aliasing filter), which will automatically protect you from any aliasing, no matter what kind of sample rate you choose. I believe that the filter will be set to the value of your sample rate times a factor of 0.4.

There are several useful resources for information on filters:

- DC HD filtering

- The filtering chapter of the Sirius technical reference manual

- Our newest digital filter is described in the Zero phase filter manual

- Filters PRO training

Let me know if you need anything else.

Helmut O'Brian

Posted on 06.06.2017 11:35


Thanks a lot for your answer. That's perfect !



Helmut O'Brian

Posted on 07.06.2017 12:15

Hi again,

I have the same question for a KRYPTON LV module.

I found this text :

"24bit delta-sigma with 20kHz/1kHz anti-aliasing filter"

Is the acquisition circuit the same as in SIRIUS hardware ? I mean : Analogue filter (20 kHz ? 1 kHz ? Why ? When ?) -> oversampling (yes 16) -> and then digital filtering at fs/2 ?

Thanks again.


DEWESoft Support
Technical support
Posted on 21.06.2017 07:04


the documentation for the Krypton filters is a bit lacking in the moment, but there is a plan to create a document which will cover all filters across the Krypton devices. The Krypton hardware filters have been changing a bit, but the current iteration features a 20 kHz low pass hardware filter for the Krypton STG and LV, the Kryton TH, RTD have a 3 kH low pass analog filter while the DIO units don't have hardware filters.

Other than that, the process is pretty much the same, featuring oversampling and digital (software) filters, like you've suggested yourself.

Luke Fredenburg

Posted on 20.11.2017 22:12


So I have a question regarding the Low Pass Filter for the STG Modules. The TH Modules have a Low Pass Filter option but the STG Modules don't. So I was wondering if there is a setting or option that I'm not seeing to manually set the filter for the STG Module. I'm taking data at 100 milliseconds and when I graph the data I have to make trend lines before I send this data out. I'm not having this problem with the temperatures, but the pressure readings have quite a bit of noise. There is an option when you measure data to have an Average Block Size of 10 Seconds but I can't use that for all of my recordings because it's too big of a data gap. A 1 Second Average Block Size would be perfect for what I'm doing. So a recap.

A.) Is there a low pass filter option for the STG (Pressure Transducer) Module, I'm only seeing this option for the TH (Thermal Couples) Module?

B.) Is there a way to change the Average Data Block Size from 10 seconds to 1 second?

Helmut O'Brian

Posted on 21.11.2017 14:55

Same questions for KRYPTON-RTD filtering.

Helmut O'Brian

Posted on 04.10.2018 12:47
Same questions for KRYPTON-RTD filtering.

No answers for this one and for the questions of Luke Fredenburg ?

DEWESoft Support
Technical support
Posted on 17.10.2018 10:51

Dear Luke and Helmut, 

we apologise for late response. The KRYPTON-STG have only one option of HW filter 20kHz. The KRYPTON-STGv2 have more additional options. See attached picture. 

I talked with the developers and they told me KRYPTON-RTD don't have any HW or SW filters.  

If you use our statistic you can lower the Average block size, the other way is to lower "static acquisition rate".


malisa srisiam

Posted on 18.10.2018 06:46
It is a very useful article. Interesting and new knowledge, too. Thank you very much.




Henrik Holst

Posted on 18.09.2019 07:11

@DEWESoft Support

Hello. The links do not link correctly. I would like to find more detaild information about how the AA-filter works. I have tried on Google, the manual and the search function on the Dewsoft web page, but Im unable to find it. Also the other analogue filter charachteristics are of interest, where can I find it?

Henrik Holst

Posted on 18.09.2019 07:14

@Henrik Holst

Attached files:
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