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<p>For the hardware interlock system, we use the magnus formula.</p>
<p>However to have a sensible number, RH must always be a positive
number. <br>
</p>
<p><a moz-do-not-send="true"
href="https://www.calcunation.com/calculator/dew-point.php">The
formula fails with a negative number.</a><br>
</p>
The majority of the EPICS sensors are showing slightly negative
values.<br>
<br>
In the hardware interlock system, we limit the lowest possible RH to
.01% for the calculation.<br>
<br>
Also, we currently display the dew point temperature differential on
the screens. Showing the actual dew point rather than the
differential would make it more clear for the users.<br>
<br>
<br>
<br>
<br>
<br>
<br>
<div class="moz-cite-prefix">On 5/21/2018 3:12 PM, Brian Eng wrote:<br>
</div>
<blockquote type="cite"
cite="mid:448031820.1015199.1526929971396.JavaMail.zimbra@jlab.org">
<pre wrap="">This is only for the software (VME) interlocks...
The simple one should really only be used when RH is >50%
So they should probably all be changed to magnus.
The formula looks like it's calculating the dew point correctly on the expert screen.
I'm not so sure about the dew point interlock though, that seems wrong.
As an example for SB6 H1
RH ~ 2%
T ~ -10C
Dp ~ -35C (magnus, simple says -5C)
DewTempDiff ~ 50C (shouldn't it be 25C?)
----- Original Message -----
</pre>
<blockquote type="cite">
<pre wrap="">From: "Yuri Gotra" <a class="moz-txt-link-rfc2396E" href="mailto:gotra@jlab.org"><gotra@jlab.org></a>
To: "dsg-svt" <a class="moz-txt-link-rfc2396E" href="mailto:dsg-svt@jlab.org"><dsg-svt@jlab.org></a>
Sent: Wednesday, May 16, 2018 9:18:52 AM
Subject: [dsg-svt] Dew point calculation
</pre>
</blockquote>
<pre wrap="">
</pre>
<blockquote type="cite">
<pre wrap="">Hello Peter,
Could you please check the dew point calculation.
In the CSS for T=7 C and RH=5% the dew point difference is 19 C which
means the dew point is -12 C.
These calculators give the dew point at -30 C.
<a class="moz-txt-link-freetext" href="http://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/relhum.html#c4">http://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/relhum.html#c4</a>
<a class="moz-txt-link-freetext" href="http://www.dpcalc.org/">http://www.dpcalc.org/</a>
Thank you
</pre>
</blockquote>
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</pre>
</blockquote>
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