Greenhouse Datalogging Advice Sought

Howard R. Hansen hrh at srv.net
Sun Jan 21 20:06:52 EST 1996


In article <jea1-1701961620360001 at btigrfx2.cit.cornell.edu>, jea1 at cornell.edu (John E. Austin) says:
>
> Would any of you kind people out there be willing to share (via
> followup or email) your experience w/ temperature logging and alarm
> devices?

I am amazed somebody else hasn't already suggested you investigate using a
Datalogger in your application.  But as I haven't seen any mention of using
a Datalogger in your application yet, here is my 2 cents worth.  As I am most
familiar with Fluke Dataloggers the following comments are based on the
capability of Fluke Dataloggers.  However, other companies manufacture
Dataloggers.  Dataloggers are data acquisition systems with everything in
one box.  Scanning, A/D conversion, electrical to enginerring units
conversion and printing.  There main use is in applications that have
a lot of points to scan and the time between scans is measured in minutes.
Dataloggers have excellent noise rejection capability because they use an
integrating A/D Converter and differential inputs.

> 1.  Poll and record to DOS-readable disk readings from 20 thermocouples
> and about 10 millivolt inputs once every 5 minutes, 24/7, w/ highest
> reliability.  Provide a realtime display of these readings.

Yes, a Fluke Datalogger can poll and record to a Dos-readable disk from 20
thermocouples and 10 millivolt signals once every 5 minutes, 24 hours a
day 7 days a week.  The basic model does not have a floppy disk drive but
higher price models come with floppy disk drives.  A datalogger has a front
panel display you can use to monitor one temperature or by pressing front
panel keys you can sequentially display all of the readings in your scan
list.

> 2.  Check each input against customizable high and low boundaries.

You can set high and low alarms for all inputs.

> 3.  Should any channel go out of bounds, the device or system needs to
> close 2 contact closures (local and remote alarm).  We also need to be
> able to easily identify which channel has gone out of bounds, even after
> the temperature has returned to in-bounds.

You can add an alarm output module to a Fluke Datalogger to obtain your 2
contact closures.  You can configure a Fluke Datalogger to print alarm
readings to a paper tape.  This will give you the capability to easily
identify which channel has gone out of bounds, even after the signal has
returned to its normal range.

> Nice, but not essential, specs:

> 1.  Capture and hold 24hour min and max for each channel.

I am not sure about this one but I suspect a top of the line Fluke
Datalogger, one with additional computation capability and adds
approximately $4000 to the cost, can provide this capability.

> 2.  Self-rebooting.  Priority placed on continuing monitoring and
> alarming, rather than on crashing when one datapoint is missed.

I don't know about self-rebooting.  But you can connect a battery to a
Fluke Datalogger and keep it from shutting down during power outages.
I have never seen a Fluke Datalogger miss a point so there is no reason
to think missing a datapoint will cause a crash.

Fluke has a World Wide Web site but because it is still under development
it does not provide any information on dataloggers yet.  Hence for
additional information on Fluke Dataloggers I suggest you call your local
Fluke sales representative.  Approximate cost for a datalogger is $10,000.

> Any help here would be greatly appreciated.  If there seems to be  
> interest, I will summarize and post.

I am interested in seeing a summary of the information you obtain on this
thread.                     H. R. Hansen




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