Can I use the signal I want to measure as a start trigger?

[Basa]

Hello.
I use a PCI6602 counterboard for period measurement with the 2 counter wide range method. Because of missing synchronization the first value in the returned array is incorrect. The signal to be measured is a variable digital TTL signal. Is it possible to use this signal as a start trigger to achieve a correct first value? Or does the measurement restart every time a new rising edge of the signal to be measured appeares? If so, how can I discard the first value?
Thank you very much!

[Kevin_Price]

I'm not sure I know what you mean by the "2 counter wide range method." Since you mention an array of values, it sounds like a buffered period measurement -- but that doesn't require a 2nd counter.

When performing a buffered period measurement, the first value's meaning and usefulness depends on whether the operation is triggered.

A) Untriggered operation - the first value is the # of source edges seen from the instant of the software call that "arms" the counter until the first gate edge. This value is meaningless in many applications and you can discard it using the 'Array Subset' function in the array palette.

B) Triggered operation - the first value is the # of source edges seen from the instant of the hardware trigger edge until the fir
st gate edge. This value is much more likely to be meaningful.

You had other questions about the start trigger.

First, for a buffered measurement, there is no retriggering. Only the first trigger edge has any effect on the acquisition. Retriggering is only supported for pulse generation where each trigger edge initiates a single pulse.

Second, while you're allowed to specify the same external signal as both a start trigger and a gating signal, I don't see much advantage. Maybe you can describe what you would expect as a "correct first value?"

Good luck!

-Kevin P.

[Basa]

I was able to solve the problem by using the functions in the array palette. Thanks for your further advices.

[Kevin_Price]

Basa,

In another thread (3 simultaneous counters) you referred to 3 channels of measurement. If that's part of the same app as this thread here, I'd change what I said here earlier about the start trigger.

I'll assume you want the timing information for the 3 channels synchronized. To accomplish this, you probably need to use a start trigger.

If your trigger and gate are sensitive to the same edge of the same signal, you may get a race condition. If the pulse you'd like to use as a start trigger and as a gate signal has a consistent width, I'd recommend tri
ggering off the leading edge and setting the gate to be sensitive to the trailing edge. The very first entry in the array for that channel will be the pulse width itself; all other entries would be periods.

-Kevin P.