How do you count the frequency of a boolean signal?

[Will15648]

Hi, I'm new to LabVIEW, so I suspect this is propbably quite a simple problem.

I'm developing an optical tacometer for a model gas turbine engine. I have a boolean signal in labview which is switching at a frequency between 4 and 26Hz. I need a live readout of the frequency of this signal.

Does anyone know how I could do this? Any help would be really appreciated!

Many thanks

Will

[deskpilot]

How are you acquiring the signal from the tach?

Message Edited by deskpilot on 03-10-2010 11:59 AM

[aeastet]

How are you truning on the boolean? What does your code look like so far? How accurate does the frequency need to be?

I guess I would make an array of time and boolean state and get a running average for the cange in time vesres the state of the boolean.

[Will15648]

The Boolean signal is coming from the digitial input of an I/O board, which is triggered by a phototransistor. The signal is acquired thorough ActiveX.

[Will15648]

Because the frequency of the signal is so low, I imagine the update frequency must also need to be quite low. If the system gave an updated frequency reading every 2 seconds, that would be great.

The system doesn't have to be that accurate. ±5% would be okay.

Thanks for your help.

[Nihil]

frequency = event/time

so basicaly what you need is to take differences of time and then invert the value.

i'd try with an event structure.

advice: make sure you are always counting the transition from 0 to 1, or from 1 to 0. that is the instant at which the boolean variable goes from false to true or viceversa.  

[Will15648]

Can you suggest any VIs to get me started? I've found a VI which detects the transition of a boolean source from TRUE to FALSE, or visversa. Could this form part of the solution?

Thanks for your advise

Will 

[herrlin]

Will

Can you post the VI you are using to capture the boolean input. May spark some ideas.

Herrlin

[aeastet · Accepted solution]

This vi should work for you

[Will15648]

Works perfectly! Thanks very much.