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Sensing temperature is one of the most
common and easiest applications in a
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control system. Here we are in an IT
server room and like most server rooms
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no one really comes in here all that
often. So what happens if the
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air-conditioning fails? You really only
find out about it when servers start to
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overheat and fail. Even if we don't
control the room temperature it sure
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would be nice to monitor it. Well in this
video workshop we'll show you how easy
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it is to sense the room temperature and
move that data into a software
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application. So let's head back to the
workshop and get started.
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Here we are back in the workshop. Before
we start hooking things up let's start
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with the big picture. What's the signal
path from a high level? Well here's a
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block diagram of what we're going to do.
We're going to take a temperature sensor
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which is an electrical signal and we're
going to convert that to digital data
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suitable for use in any number of
software or cloud applications. Now for
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this workshop I'll be using this SNAP PAC
Learning Center it's basically a SNAP
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PAC system with a controller, several i/o
modules, and a rack. We use it for
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training here at Opto 22. This panel
simulates some typical i/o signals like
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a meter, potentiometer, temperature sensor,
LEDs, and switches. The controller is
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running a control strategy that's loaded
into its memory and I'll be using PAC
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Control on this Windows laptop to
configure the strategy and then download
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it to the controller. You can get your
own Learning Center and free PAC Control
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software at workshops.22.com. Now
arguably one of the easiest ways to
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sense temperature is with an integrated
circuit temperature device or ICTD.
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ICTDs excel and applications that require
fairly accurate readings from -40
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to +100 Celsius which is perfect for
our server room temperature. The ICTD
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sensor outputs a micro amp signal that's
proportional to its temperature. Who
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cares - why is this important? Well what it
means is that you can get an accurate
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temperature reading up to 600 meters
away. So you might be able to use some
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dark cat5 cable that you've already got
running through your building to pick up
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several temperature sensors from
different locations. The temperature
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input modules come in 2, 4, or 8 channel
and they can work with different types of
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temperature sensors like this ICTD
thermo-well sensor. ok now when it comes
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time to actually hook things up you'll
find the wiring diagram on the side of
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the module and the wiring on this one is
actually pretty hard to get wrong.
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There's only two wires so for this two
channel SNAP- AICTD module simply
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connect the white wire to Terminal one
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and the black wire to Terminal four. Now
I'm going to add the temperature module
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to the i/o rack by snapping it into
place. I'm going to put it in position
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seven here on the end. So that's the
wiring and the module installed. So now
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let's go to the laptop now and configure
the software. Here we are in PAC Control
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and we've already got our rack
configured. So now let's double-click on
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the empty slot in position seven and
we're going to add an analog input
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temperature module. In this case it's a
SNAP-AICTD. We're going to double click
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on the first one on the module to open
the point configuration dialog. Now we'll
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give the temperature sensor a tag name
like "server room temp". Now this is where
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the temperature sensor is given a
meaningful name for your software
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application or cloud services. So make
sure you choose your name accordingly.
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Now click on the debug button to
download the configuration on your
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controller. Click yes to save and yes
that you've made a change and the
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download process will start. Once it's
done click run to execute the new
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strategy.Let's open up the debug window
by double clicking on the point and we
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can confirm that we've configured our ICTD sensor correctly by viewing the
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temperature in real time right here. Now
at this point we can use PAC Control to
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monitor the temperature value and sound
an alarm if it goes out of limits or we
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could just log the temperature in the
controller. Using a tool like NODE-Red we
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could write that value to a database
either locally or in the
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cloud or we could send it to any number
of cloud services like IBM Watson or
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Microsoft Azure. For more information
about temperature sensing check out our
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primer on i/o solutions for temperature
monitoring. It's form number 1767 on our
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website. But you can also find a link to
it on workshops.opto22.com and there
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you'll also find a list of the parts
that I used for this workshop. So there
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you go
the electrical signal from the
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temperature sensor has been converted to
digital data. Cheers mate!