Counting cycles of a chamber

[voiceburg]

I need a simple way to measure the number of times a temperature
chamber reaches it's peek temperature. I'm cycling from 90 to -55 6000
times and need to keep an accurate count in labview. I'm going to be
setting at each extreme for 30 minutes and taking data every 5
minutes. So how do I increment a counter just one time each time i hit
my 90 degree mark?

Thanks to all for any help

[Darren Lloyd]

If I am understanding your question right, it will take about 10 months for
this test to be completed. Why not just wire a latching circuit that uses 2
DPDT relays. That latch could toggle with the power from your
cooling/heating system. The count would not be affected by the heater or
cooler coming on or off during the time that you are holding the
temperature. The latch would only change states when the opposite system is
powered up. The latches could feed into an off-the-shelf 12V counter wired
to a battery(in case of a glitch in the power you won't loose the count).

As far as recording the temperature every 5 minutes, why would you need this
for such a long period of time? Why not just record sections of it
throughout the test. It looks like a waste o
f time to be recording such
large amount of repetitive data.


"BILL B" wrote in message
news:b981045d.0204021349.15024e04@posting.google.com...
> I need a simple way to measure the number of times a temperature
> chamber reaches it's peek temperature. I'm cycling from 90 to -55 6000
> times and need to keep an accurate count in labview. I'm going to be
> setting at each extreme for 30 minutes and taking data every 5
> minutes. So how do I increment a counter just one time each time i hit
> my 90 degree mark?
>
> Thanks to all for any help

[Rob Cole]

That may be an inaccurate count. The chambers that I have worked with will use both systems (heating and cooling) while performing ramp operations. Take the heating cycle: While going from a low temperature to a high temperature, the heaters will come on, but as the temperature approaches the endpoint of the ramp, the cooling system will come on so the temperature does not overshoot by too much. It's either that or ramp the temperature over a LONG time. If it is a long ramp, then I think your latch system would be a good way of doing it.
As for the recording - he may need data to show that the test was performed correctly. Admittedly, every 5 minutes over this amount of time will be a HUGE amount of data. As long as he is taking readings, a simple VI can
be created to "test" the data and increment a counter on screen for each cycle.
Borrowing your latch concept - a while loop with a case structure in it would work. The counter increment would by in a case that looks for the temperature to reach a certain value (for example the high temperature) and call another case that looks for the temperature to reach a different value (for example the low temperature) then call the first case. This would get rid of any extra counts from the temperature oscillating around one dwell or the other.

I just re-read his question and he says that he's "taking" data every 5 minutes, not necessarily recording the data every 5 minutes. Recording a subset of this would be a good idea.

Rob

[JPG]

You can take a reading every 5 minutes and save this data along with a timestamp. This will be a long test,
so there is a good chance for a computer crash or power failure. You do not want to lose the data.
Then you could write a vi that reads back the data, and plot on a graph indicator. You can use the peak detector vi to count the number of cycles.
good luck,

guindon_jp@hotmail.com