EDAboard.com | EDAboard.de | EDAboard.co.uk | WTWH Media

HELP:Low-pass filter on frequency counter

Ask a question - edaboard.com

elektroda.net NewsGroups Forum Index - Electronics Equipment - HELP:Low-pass filter on frequency counter

caius
Guest

Fri Jan 21, 2011 7:07 pm   



Hi all,
I have to made some measurements with a frequency counter (model VC3165) on
low frequencies (up to 60 Hz) .I know that in case of low frequency
measurements a low-pass filter is needed in order to obtain stable and
precise readings.
My frequency counter has only an AC/DC button (to be used with a low-pass
filter as said in the service manual) but it doesn't have an integrated
low-pass filter (many counters have it).

I built some simple RC filter ( using a resisitor and a capacitor) with
various cut-off frequncy ( I tried 15 Khz and 50 Khz) but I alway obtain
floating and not precise readings on low frequencies.
How can I solve this problem?Maybe using a low-pass filter like these(very
expensive IMHO)?:

http://cgi.ebay.com/AGILENT-HP-10856A-LOW-PASS-FILTER-KIT-5KHz-50KHz-500KHz-/120668081898?pt=LH_DefaultDomain_0&hash=item1c1860ceea

or building a proper one (but as said before simple RC filters didn't work)?

Rich Webb
Guest

Fri Jan 21, 2011 9:14 pm   



On Fri, 21 Jan 2011 19:07:56 +0100, "caius" <briccus_at_yahoo.it> wrote:

Quote:
Hi all,
I have to made some measurements with a frequency counter (model VC3165) on
low frequencies (up to 60 Hz) .I know that in case of low frequency
measurements a low-pass filter is needed in order to obtain stable and
precise readings.
My frequency counter has only an AC/DC button (to be used with a low-pass
filter as said in the service manual) but it doesn't have an integrated
low-pass filter (many counters have it).

I built some simple RC filter ( using a resisitor and a capacitor) with
various cut-off frequncy ( I tried 15 Khz and 50 Khz) but I alway obtain
floating and not precise readings on low frequencies.
How can I solve this problem?Maybe using a low-pass filter like these(very
expensive IMHO)?:

http://cgi.ebay.com/AGILENT-HP-10856A-LOW-PASS-FILTER-KIT-5KHz-50KHz-500KHz-/120668081898?pt=LH_DefaultDomain_0&hash=item1c1860ceea

or building a proper one (but as said before simple RC filters didn't work)?

You may want to look at the wave shape. If it's changing slowly and if
there is high frequency noise riding on the input (there's always some)
then you may be getting multiple trigger events as the signal crosses
the trigger level.

If this is the case, you might improve things by inserting a comparator
with some hysterisis between the signal and the counter. Using the
comparator may give the counter a sharper edge to work with and the
hysterisis will improve your noise immunity.

--
Rich Webb Norfolk, VA

elektroda.net NewsGroups Forum Index - Electronics Equipment - HELP:Low-pass filter on frequency counter

Ask a question - edaboard.com

Arabic version Bulgarian version Catalan version Czech version Danish version German version Greek version English version Spanish version Finnish version French version Hindi version Croatian version Indonesian version Italian version Hebrew version Japanese version Korean version Lithuanian version Latvian version Dutch version Norwegian version Polish version Portuguese version Romanian version Russian version Slovak version Slovenian version Serbian version Swedish version Tagalog version Ukrainian version Vietnamese version Chinese version Turkish version
EDAboard.com map