Maintenance Technology September 2016 - 44
WORKFORCE ISSUES
Clear Up Your HOA Confusion
FOR PLANTFLOOR personnel,
the HOA (Hand-Off-Auto)
switch represents one of
the most misunderstood
components of an
industrial-control system.
The problem is exacerbated by the fact that a site
often employs multiple
switches in different areas
of the plant to control a
single field device. According
to Josh Niemi, P.E., of Normal,
IL-based SCADAware Inc.
(scadaware.com), this is a recipe
for confusion: If one switch is in
the Hand position and the other
is in the Auto position, how is the
device going to be controlled?
The problem increases, he wrote
in a Feb. 2016 blog post, when a
PLC or SCADA system is involved.
Does Auto translate as "controlled
by the SCADA system?" If so,
what term should be used if the
SCADA system allows personnel
to manually set a fixed PLC output
to control the field device rather
than allowing the PLC itself to
automatically set the output?
Niemi believes this lingering
confusion may stem from use of
the single term HOA. Using the
terms Location of Control and
Mode of Control, he suggested,
could help clear it up.
The inherent problem with
Josh Z. Niemi, P.E., is a senior
engineer with SCADAware Inc.,
Normal, IL. For more information about industrial-control topics,
contact him at niemi@scadaware.com
or visit scadaware.com.
44 |
MAINTENANCE TECHNOLOGY
Is your approach to
Hand-Off-Auto switch use
confusing workers?
Location of Control
refers to the place from which
a motor or other field device
is being operated. Location
nomenclature includes:
■ Hand: Device is operated
directly at the starter.
■ Local: Device is operated by
Start/Stop contacts near the
motor.
■ Remote: Device is operated
by a PLC or other device at a
distance away from the process.
■ Off: No location control is
allowed.
Mode of Control
refers to the control strategy
used to operate a device. Mode
nomenclature includes:
■ Auto: Device is controlled
based on a set of process
conditions.
■ Manual: Device is controlled
by fixed operator input.
■ Off: Device is still energized
but control is currently
disabled.
the term HOA, according to Niemi, is that
it combines Location of Control (the
designation for hand/manual operation)
with Mode of Control (the designation
for automated operation) on the same
switch. In older DCS (Distributed
Control System) technology, this
may not have been much of a
problem because here may have only
been a single device switch (there
weren't multiple ways to control it)
and the term Hand meant Location of
Control and Mode of Control. With the
larger, more complex systems in use today,
however, this old-school approach doesn't
work.
Distinguishing between Location of
Control and Mode of Control, Niemi noted,
leads to control switches that can accommodate a wide range of systems. For example,
if a control switch is being used to select
between controlling directly at a device or
by a remote PLC or SCADA system, an LOR
switch (Local-Off-Remote) or HOR switch
(Hand-Off-Remote) would probably be best.
But if the control switch toggles between an
operator-adjustable output and a variable
output based on a process condition, an
MOA switch (Manual-Off-Auto) would be
the better fit.
Regardless of a plant's chosen control
system(s), the most important thing to
avoid is multiple switches with redundant
labeling (multiple HOR switches, or mixing
Location and Mode terminology on the
same switch, such as a Manual-Off-Remote
or Local-Off-Auto switch). Unless a very
specific application demands redundant
switches or mixed-terminology switches,
Niemi emphasizes that it's better to avoid
them altogether.
Find Niemi's complete blog post with
detailed examples on understanding HOAs
at scadaware.com/blog. MT
-Jane Alexander, Managing Editor
SEPTEMBER 2016
http://www.scadaware.com
http://www.scadaware.com
http://www.scadaware.com/blog
Table of Contents for the Digital Edition of Maintenance Technology September 2016
Editorial
Uptime
On The Floor
Old-School Approach To New-World Technology
Art Meets Reliability Science
Commit To Safety
Robot-Human Interaction Getting Safer
Sanitary, Stainless Conveyors Not The Same
Reduce Hidden Process-Safety Costs
Pace Your Reliability Program
Win The War With 'Lubrication By Design'
SAP Tips And Tricks
Understand Pump Vibration
Select The Right Relay
Bearing Care
Clear Up HOA Confusion
Potato Waste Becomes Clean Water, Energy
Products
Showcase
Ad Index
Final Thought
Maintenance Technology September 2016 - 1
Maintenance Technology September 2016 - Cover1
Maintenance Technology September 2016 - Cover2
Maintenance Technology September 2016 - 1
Maintenance Technology September 2016 - 2
Maintenance Technology September 2016 - 3
Maintenance Technology September 2016 - Editorial
Maintenance Technology September 2016 - 5
Maintenance Technology September 2016 - Uptime
Maintenance Technology September 2016 - 7
Maintenance Technology September 2016 - On The Floor
Maintenance Technology September 2016 - 9
Maintenance Technology September 2016 - Old-School Approach To New-World Technology
Maintenance Technology September 2016 - 11
Maintenance Technology September 2016 - 12
Maintenance Technology September 2016 - 13
Maintenance Technology September 2016 - 14
Maintenance Technology September 2016 - 15
Maintenance Technology September 2016 - Art Meets Reliability Science
Maintenance Technology September 2016 - 17
Maintenance Technology September 2016 - 18
Maintenance Technology September 2016 - 19
Maintenance Technology September 2016 - Commit To Safety
Maintenance Technology September 2016 - 21
Maintenance Technology September 2016 - 22
Maintenance Technology September 2016 - 23
Maintenance Technology September 2016 - Robot-Human Interaction Getting Safer
Maintenance Technology September 2016 - 25
Maintenance Technology September 2016 - Sanitary, Stainless Conveyors Not The Same
Maintenance Technology September 2016 - 27
Maintenance Technology September 2016 - 28
Maintenance Technology September 2016 - Reduce Hidden Process-Safety Costs
Maintenance Technology September 2016 - 30
Maintenance Technology September 2016 - Pace Your Reliability Program
Maintenance Technology September 2016 - 32
Maintenance Technology September 2016 - 33
Maintenance Technology September 2016 - 34
Maintenance Technology September 2016 - 35
Maintenance Technology September 2016 - Win The War With 'Lubrication By Design'
Maintenance Technology September 2016 - 37
Maintenance Technology September 2016 - 38
Maintenance Technology September 2016 - SAP Tips And Tricks
Maintenance Technology September 2016 - Understand Pump Vibration
Maintenance Technology September 2016 - Select The Right Relay
Maintenance Technology September 2016 - Bearing Care
Maintenance Technology September 2016 - 43
Maintenance Technology September 2016 - Clear Up HOA Confusion
Maintenance Technology September 2016 - Potato Waste Becomes Clean Water, Energy
Maintenance Technology September 2016 - 46
Maintenance Technology September 2016 - 47
Maintenance Technology September 2016 - 48
Maintenance Technology September 2016 - 49
Maintenance Technology September 2016 - 50
Maintenance Technology September 2016 - 51
Maintenance Technology September 2016 - 52
Maintenance Technology September 2016 - Showcase
Maintenance Technology September 2016 - Ad Index
Maintenance Technology September 2016 - 55
Maintenance Technology September 2016 - Final Thought
Maintenance Technology September 2016 - Cover3
Maintenance Technology September 2016 - Cover4
Maintenance Technology September 2016 - 62
Maintenance Technology September 2016 - 63
Maintenance Technology September 2016 - 64
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