Author Topic: Frequency counters operation  (Read 835 times)

0 Members and 1 Guest are viewing this topic.

Offline Y2KEDDIETopic starter

  • Newbie
  • Posts: 7
  • Country: us
Frequency counters operation
« on: March 04, 2023, 04:12:54 pm »
I’ve noticed some frequency counters, when no signal is applied to the input, the display reads all zero’s, as one would expect.

Some counters display random readings, until a signal is applied, or the reset button is pressed. This is the case of a high resolution counter I bought from  e-bay. The operation literature say’s Radom display is normal operation.

Why do some counters require a manual reset and others don’t.
« Last Edit: March 04, 2023, 04:15:05 pm by Y2KEDDIE »
 

Offline pcprogrammer

  • Super Contributor
  • ***
  • Posts: 4669
  • Country: nl
Re: Frequency counters operation
« Reply #1 on: March 04, 2023, 05:10:33 pm »
Open input sensitive to noise?

No proper power on reset in the circuit?

Offline shakalnokturn

  • Super Contributor
  • ***
  • Posts: 2218
  • Country: fr
Re: Frequency counters operation
« Reply #2 on: March 04, 2023, 05:10:47 pm »
I suppose it has something to do with the way they trigger and surrounding EMI.
 

Offline xrunner

  • Super Contributor
  • ***
  • Posts: 7836
  • Country: us
  • hp>Agilent>Keysight>???
Re: Frequency counters operation
« Reply #3 on: March 04, 2023, 05:30:51 pm »
I’ve noticed some frequency counters, when no signal is applied to the input, the display reads all zero’s, as one would expect.

Some counters display random readings, until a signal is applied, or the reset button is pressed. This is the case of a high resolution counter I bought from  e-bay. The operation literature say’s Radom display is normal operation.

Why do some counters require a manual reset and others don’t.

If the input isn't terminated, then it's going to receive signals from the environment at the center pin of the input connector, however poor of an "antenna" that tiny piece of metal is. Now, they may be very small signals or they may not be - it depends on your local environment and the sensitivity of the unit. Try terminating with a 50 ohm termination and see if the random signals stop.
I told my friends I could teach them to be funny, but they all just laughed at me.
 

Offline edpalmer42

  • Super Contributor
  • ***
  • Posts: 2351
  • Country: ca
Re: Frequency counters operation
« Reply #4 on: March 04, 2023, 06:59:18 pm »
The other thing you can do to suppress the garbage displays is to move the trigger level slightly off zero.  It won't affect a normal reading since the input will hopefully be at a much higher level.  Note that this type of garbage display could be caused by either external signals or internal noise or a combination of both.

Ed
 

Offline factory

  • Super Contributor
  • ***
  • Posts: 3214
  • Country: gb
Re: Frequency counters operation
« Reply #5 on: March 04, 2023, 07:07:40 pm »
This is normal for some of the prescaler/divider ICs, for example the Plessey SP8703, which will self oscillate with no input, it can be fixed by adding a resistor to one of the inputs, but this reduces the sensitivity.

David
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf