signal level for pulse width measurement

[Pechmann]

Hello,

I am measuring the pulse width with the M6251 by counter (CI Pulse Width)

I understand that the digital input is working on TTL levels (0,8V low 2,4V high).

Can it be exactly said at which signal level the pulse width is measured?

Thanks,

Ralf

[Marco_Brauner]

Electrical Characteristics

Level                                             Min     Max
Positive-going threshold (VT+)       —      2.2 V
Negative-going threshold (VT–)    0.8 V    —
Delta VT hysteresis (VT+ – VT–)  0.2 V    —

Marco Brauner AES RF NIG

[Pechmann]

Thanks for your answer, Marco.

Just to make sure I got it right:

When I configure falling edge the pulse width output is the time between

a. the falling edge passes the 0.8V threshold

b the rising edge passes the 2.2V threshold

Thanks for your patience,

Ralf

[Marco_Brauner]

measuring period is from falling/rising edge to next falling/rising edge. 

What you mentioned would be Half-Period. Falling to rising.

Marco 

[crossrulz]

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@Marco_Brauner wrote:

measuring period is from falling/rising edge to next falling/rising edge. 

What you mentioned would be Half-Period. Falling to rising.

Marco 

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Pechmann is asking about Pulse Width measurements,  not Period measurements.

[John_P1 · Accepted solution]

In reality the transition from low to high (or vice versa) is somewhere in between 0.8V and 2.2V.  It is not specced exactly where this will be (though you would be able to get a better idea if you have an analog source that you can slowly increase until you see the line state change).  

This is why fast rise times are important for accurately measuring digital signals.

Best Regards,

[Pechmann]

Thanks for your answers.

Maybe I will try to measure the levels as John suggested.

But I surely have to find an alternative approach for pulse width measurement

because the need of configurable levels was added.

Have a nice day,

Ralf

[johnsold]

Ralf,

If you need configurable levels, then you need to to an analog acquisition and then use Pulse Measurements.vi from the Signal Conditioning >> Waveform Measurements palette. Make sure you sample fast enough to get several sample during the transitions so that you can get reasonably accurate measurements.  Digital acquisition by definition reduces the data to two levels - low and high.

Lynn