Unable to read frequency of a tone signal with a frequency meter.

[Arouse1973]

If that trace is 20 mV per division then it's greater than 80 mV. Just out of interest what wave shape were you using from your signal generator when you did the test with it?
Cheers
Adam

 

[Arouse1973]

Don't know if this is of use to you. It explains a bit about some of the setting. But I guess you know most of this stuff already.

Cheers
Adam

 

[Alby]

If that trace is 20 mV per division then it's greater than 80 mV. Just out of interest what wave shape were you using from your signal generator when you did the test with it?
Cheers
Adam

That's true Adam. That trace is the raw signal at the output of the circuit. In one of my previous post I had built a voltage divider and put that raw signal though it to knock the signal down to 43 mv to see if the freq meter would read it and it didn't.

I was using a regular sine wave output @ 20 mv, 67 hz on the Audio signal generator. I was using the Audio signal generator just to check the frequency counter, The Freq counter reads the Audio signal generator with no problem.

 

[hexreader]

In addition to the signal to be measured, did you also provide ground connection from your circuit to the frequency counter, or did you assume that the frequency counter is grounded?

That frequency counter is unusual for a mains device in that the BNC outer connections are not grounded.

Can't think of any other reason to explain your symptoms.

 

[Alby]

In addition to the signal to be measured, did you also provide ground connection from your circuit to the frequency counter, or did you assume that the frequency counter is grounded?

That frequency counter is unusual for a mains device in that the BNC outer connections are not grounded.

Can't think of any other reason to explain your symptoms.

Yes, using the test lead provided by the manufacture. I did assume that the frequency counter was grounded.

I think I understand what your saying.

Other electrical grounding has also been considered but because of everything being plastic now days, there are no external lugs to connect earth ground the meter. I assumed that the power cord grounding is internally connected in some fashion, most likely to an isolated power supply. I know that the test lead grounding clip is connected to the BNC outer connector, but the BNC is isolated from power grounding internally. In other words, the internal frequency counter circuit/pcb is above or isolated from the 120 vac power grounding. The circuit I'm working on is being powered by a isolated, regulated, DC power supply.

Is your question suggesting that I use a different test lead and maybe connect the meter, the radio I'm working on and the DC power supply to common earth ground?

 

[hexreader]

No need for an actual ground connection, just make sure that a two-wire test lead is used for frequency counter, not a single wire.

Your reply suggests to me that you are already doing the right things, so I now have no idea as to where the problem may be.

 

[BobK]

Have you connected it to both the scope and the counter to make sure the counter is not loading the signal and degrading it, or even stopping the oscillator?

Bob

 

[Alec_t]

The write-up for the frequency counter says:
"Channel A (0.01Hz to 50 MHz)
Frequency range : DC couple 0.01Hz to 100 Hz, AC couple 100Hz to 50 MHz
Sensitivity :
"DC" 0.01 Hz - 1 Hz ≤ 500m Vp-p , 1 Hz - 100Hz ≤ 80m Vrms
"AC" 100 Hz - 50 M Hz ≤ 80m Vrms "

Should that be interpreted as requiring 80mV minimum or maximum? I think the former, especially in view of the sensitivity figure given for 0.01Hz-1Hz. Try a bigger signal than what you've been feeding it so far.

 

[Alby]

Have you connected it to both the scope and the counter to make sure the counter is not loading the signal and degrading it, or even stopping the oscillator?

Bob

Did that. The signal on the scope was there while sanctimoniously trying to read the frequency with the freq counter. With a direct connect with the freq counter the signal dropped 1/10th of a volt. The signal was still clean and didn't change form. I'm beginning to think this freq counter isn't good enough to do the job.

 

[Alby]

The write-up for the frequency counter says:
"Channel A (0.01Hz to 50 MHz)
Frequency range : DC couple 0.01Hz to 100 Hz, AC couple 100Hz to 50 MHz
Sensitivity :
"DC" 0.01 Hz - 1 Hz ≤ 500m Vp-p , 1 Hz - 100Hz ≤ 80m Vrms
"AC" 100 Hz - 50 M Hz ≤ 80m Vrms "

Should that be interpreted as requiring 80mV minimum or maximum? I think the former, especially in view of the sensitivity figure given for 0.01Hz-1Hz. Try a bigger signal than what you've been feeding it so far.

My manual says the same thing. On the "A" channel the sensitivity for DC coupling 1 Hz - 100Hz is less than or equal to 80m Vrms. I don't know how that would be interpreted as min or max.The signal in this circuit is much greater than that, so why would I want a bigger signal?. I built a couple of resistive circuits to attenuate the signal to meet the meters requirements. One to attenuate the signal to 22m Vrms and another at 43m Vrms. Still the meter wouldn't read it. I know the signal is there because I was scoping it as I was trying to read it with the freq meter. As I told BobK, I think the freq meter isn't up to the job of reading it. I'm going to have to barrow a good freq meter to see if mine is funky.

 

[BobK]

A sensitivity of <= 80mV means 80mV is the minimum signal guaranteed to be accepted by the counter, not the maximum.

Bob

 

[Alec_t]

Glad someone agrees

 

[Alby]

I stand corrected. Sorry

 

[Alby]

In hopes that I can clear the air, I've drawn a schematic of the circuit I'm dealing with. I included the results from the oscilloscope probing during circuit activation via the PTT (push to talk) button. Forgot to add pin's 7 and 14. Pin 7 is ground and 14 is VDD in this MC14001B chip.

I've tried everything suggested in this thread but nothing seems to work. Am I misunderstanding something or do I have a funky frequency meter?
Ignore note at bottom of schematic drawing page about dc coupling, forgot to erase it.

 

[Alec_t]

Your frequency meter ought to respond to signal A (at pin 11) correctly, providing the meter input impedance is at least a few kΩ and the circuit/meter grounds are commoned.

 

[Alby]

Bad news and good news Alec_t.

Bad news,I tried your recommendation and it didn't work.

Good news, I got visited by a old friend last night and got into a conversation about my problem of not being able to read a frequency with my freq meter. ( My friend is an accomplished electronic tech whom knows way more than I do.) He sat down and conducted basically the same tests I had done with the same results. He turned to me and said the frequency isn't working right. He then took the freq meter apart and probed around in it. Did some soldering on a couple of components, tried testing the circuit I'm working on and eureka, it read the frequency.

I have to say though, I learned a great deal in this thread. Thank you all for your time and input, it was educational and not soon forgotten. Time now to move on.

Al

 

[Arouse1973]

Good News!

 

[Alec_t]

Glad you got it sorted.