Back in June, I mentioned the Pumping Systems Matter initiative
and the related free magazine, Pumps and Systems.
I just got notice of the
September issue being available and when I downloaded it,
discovered that it had a pretty good article on 4-20 ma current
loops including a discussion of the basic operating theory,
intrinsic barriers, applications where the loop serves multiple
devices, isolated inputs, and PID versus P only control.
The article discusses the topic in the context of the control of
pumps in a waste water plant setting rather than an HVAC
application, but the fundamentals apply across the board and the
article would likely be helpful to anyone in any industry trying to
understand 4-20 ma control loops.
Other discussions from recent issues of Pumps and Systems with
across the boards applicability include a recent article on bearing
maintenance, that included some great pictures and descriptions of
bearing problems as illustrated below. While written with a
slant toward pump, I suspect/know that similar problems can be
found in other equipment using anti-friction bearings.
There has also been a multi-part series that focused on pumps
and efficiency, starting with a discussion of pump fundamentals in
the June issue (illustrated below);
and proceeding with a discussion of pump and system interactions
in the July issue, and a discussion of pump life cycle costing
in the August issue. The current issue continues the series
by focusing on improving the efficiency and performance of existing
pumping systems. In my experience and the experience of
others, existing pumping systems are ripe with opportunities, often
yielding a big bang for the buck in terms of effort expended for
the improvements gained.
The bottom line is that industry focused resources like Pumps
and Systems are often worth exploring even if your focus is broader
than their focus because the fundamentals behind their industry
focus can be applied across a broad spectrum including your
area of interest.