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-We get occasional request for a positioner
that will work on 4-16 psi, or maybe 5-19 mAs….often
whoever is calling doesn’t know the answer to “why”,
so we just mount a unit to our test stand and double check
them. We have found that on most 90 degree applications
we can handle an extra 1-2 psi or 2-3 mA difference-either
up or down-or the more narrow or slightly wider signal
request. We have enough span and zero in the V100 or V200
to accommodate these request, but they need to be checked,
and even if we can test to them, you need to double check
them in your shop. As you start to go down in rotation
to 60-45-30 degree cams, this becomes more difficult.
Now if you are spilt ranging a valve that would be normally
3-9 psi or 12-20 mAs, your margin of adjustment is tighter….but
may be achievable. Just remember to always set the zero
first and then span….no matter what signal you are
trying to reach. The final check should be in your shop
on the actual package you plan to ship!!
-New
pricing is in affect for mounting kits effective October
1, 2008….if you have not received your price sheet
or notice, please contact us and we can get you an updated
copy.
-This cam has a special
curve that will help open the valve past what would be
called the “dead spot” in a o-port ball valve
or some plug valves. It has a 25 and 35 degree “live
load” curve depending on the side of the cam you
utilize. This in effect gives the valve a “quick
open” response so that you see flow through the
valve at a much lower signal input. We stock this cam
and when ordered with the positioner is no additional
charge, just end your ordering code with C9 instead of
the standard C1. As a spare part it is part number 400057
for either the V100 or the V200 products. Of course the
D400 digital unit has this type of curve installed in
memory and can be changed under the Configuration Level
P2.2, where you have four built in options.
-Even with MULTIPLE
attempts at communicating our new address, we still get
mail, shipments, even visitors to our old address. We
are now and will be for some time at-200 Jade
Park-Chelsea, Al 35043.
Unfortunately it is such a new address that MapQuest or
Google Maps or most GPS systems haven’t found us
yet. We are not trying to hide…call us if you need
directions…but please send returns, mail, deliveries
to the new address!!
-We’ve
had some recent questions about standard analog signals
and the loop power that is used to drive the electropneumatic
positioner. “Loop power” is considered a 24
VDC power source. While the power is independent of the
signal, they are both transmitted over two wires, and
thus sometimes called a “two wire” instrument.
The industry has become more standardized on the 4-20
mA (milliamp ere or milliamp) signal range. At one time
10-50 mA was used, but that has been replaced with the
safer 4-20 mA range. For a loop powered instrument to
work and control (modulate), you have to provide 24VDC
power and then the 4-20 mA signal. The power is just that-it
in effect “turns on” the instrument. Then
the 4-20 mA signal (current loop) controls the positioner
from zero (typically 4 mA) to 100% (20 mA). This allows
the customer to throttle the control valve from zero to
100% using the 4-20 mA signal. These loops are often referred
to as analog loops. |
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