analog voltage input

[labview1958]

I am using a NI-6025E-DAQ card. I am trying to measure a square wave signal that is 0V, 5V, 0V, 5V etc. I have connected the source to my DAQ card. I have an amplitude Vs time chart.  The analog signal on the chart is approximatly  0 and 5. Does the amplitude 0 & 5 correspond to 0V & 5V? I did not callibrate anything. Furthermore the 0 & 5 amplitude lines are wavy ranging from 0 to 1(for 0 amplitude) and 4 to 5 (for 5 amplitude). The rise and fall lines are however straight. Why is that? 

[LesHammer]

> Does the amplitude 0 & 5 correspond to 0V & 5V?

Yes

>  Furthermore the 0 & 5 amplitude lines are wavy ranging from 0 to 1(for 0 amplitude) and 4 to 5 (for 5 amplitude).

By "wavy" do you mean the straight rise and fall lines below, or "wavy" as in 60 Hz noise?

> The rise and fall lines are however straight. Why is that? 

Without knowing your circuit I can't say for sure, but that is one characteristic of a slew rate limited system - limited current driving a capacitive load (which could be a cable).

Les.Hammer@CompleteTest.com

[labview1958]

I am using a function generator as the source of the square wave signal. Below is a picture of my signal.

[URL=http://img140.imageshack.us/my.php?image=wavy9vv.png][IMG]http://img140.imageshack.us/img140/6250/wavy9vv.th.png[/IMG][/URL]

The wavy part is much more wavy then the picture.

[labview1958]

http://[URL=http://img140.imageshack.us/my.php?image=wavy9vv.png][IMG]http://img140.imageshack.us/im...

I am trfying to paste the image. This is my first time.

[Waldemar]

1st lower the frequency if the waving is slowly disappearing then you
have ringing (a "bad" circuit -> well it depends what they wanted to
do)
2nd if the wave doesn't disappear even if you lower the frequency to 0 -> then you have problems with the ground -> and this is normally referred that you have 50Hz(60Hz) hum problem (try to connect all your devices as close to each other -> or you can remove some device's ground -> don't remove all the grounds!!! -> well normally all the "hum less" connected devices have only 1 ground connected and other disconnected or they do it in some other way -> i.e. optocoupling of the signals,....)

[labview1958]

Actually I am using the one counter method to measure the frequency of the signal( 1 to 100 Hz). I am using the measure period VI. I am using the FALL time to measure the period/frequency. So far the signal varies from 10 to 50 Hz. The signal from the function generator can be detected accuratly by the LV program. However the signal from my setup tends to hang and also fluctuates from 10 to 50 Hz. When I run the signal through the DAQ card, I get a similiar signal like the frequency generator accept that it is much more wavy especially the top part. Anyone can help.

[Waldemar]

What kind of help do you really need?

Do you want to remove the wave part of the signal??

You first asked why there is this wave part.
1st option ringing -> this is a system thing -> you probably can't do much here -> except if your inputs behave like capacitors -> then put a resistor in series between the FG and you input

2nd you can have HUM coming from the ground -> this is a common problem with multiple ground connections
Reconnect you devices to the same plug or the plugs that are really close, remove some power grounds(this is a no-no if you don't know what you are doing).

Peace
Waldemar

[labview1958]

I understand that LV can only find the frequency/period of  a TTL signal. So I am trying to make my not so perfect signal to a TTL signal so that I can find the frequency/period.

[LesHammer]

> I understand that LV can only find the frequency/period of  a TTL signal.

The power spectrum vi can find the frequencies of any signal -

  - not just a TTL signal

  - and the entire spectrum (or at least samples-per-second / 2 )

There is no need to make it look like a TTL signal first.

--Les.Hammer@CompleteTest.com

[labview1958]

I have two counters on my 6025E DAQ card. I can only spare  one counter to measure the period/frequency. Can I use one counter method in the power spectrum.vi. I am actually measuring only one low fequency between 0 to 100 Hz. Can I reject all other frequency outside this range? Where can  I find the power spectrum.vi?