Anyone observing process industries these days
recognizes that they are very competitive. Pressures related to costs and
environmental concerns make daily operations more complicated. The difficulties
of finding qualified employees add another layer to the picture. Fortunately,
automation providers are doing their best to fill in the gaps by increasing the
capabilities of their products to improve basic performance. In turn, this
helps plant personnel increase their ability to automate tasks done
traditionally by instrumentation technicians that are no longer available
today.
For the purposes of this article, a modern pressure
instrument will be used as an example, but any plant looking for ways to
improve performance should be researching what new capabilities are now
available in the marketplace.
Bluetooth® technology comes to instrumentation. Bluetooth is a family of protocols, so the technology is familiar but
different for industrial applications. It
is designed to replace cables, and so it is the basis for wireless earbuds,
keyboards, mice and so on. Its use has been creeping into industrial
applications, as well. Early on, programmable logic controller (PLC)
manufacturers added it to their units so troubleshooters in a plant could make
programming changes from a laptop without having to address the safety
protocols of opening a large equipment cabinet to make wired connections. With
improvements in transmitter electronics, it is now possible and cost-effective
to add Bluetooth technology to an individual instrument. What does this mean?
To start, it is a major safety advancement
over traditional instrument maintenance using HART®. There is no need to open a
transmitter housing and connect test leads from a communicator. When a
technician carries a laptop, smartphone or tablet equipped with an appropriate
app (FIG. 1),
it will discover all Bluetooth technology-enabled instruments within a radius
of about 50 ft (15 m). These instruments can “broadcast” their presence
continuously, including operational status and alarm conditions, because the
radio operates using normal loop power.
When a technician accesses a transmitter through
the app using a password, all variables are accessible, including those related
to the process, along with alarms and diagnostic information. Each action performed
over the Bluetooth connection is sent to the transmitter, including alarm acknowledgment,
configuration adjustments, calibrations and others. Logs stored within the
transmitter can also be accessed for aiding with regulatory compliance, while protecting
against unauthorized configuration changes.
There is no longer any need to access a
transmitter directly, so there is no reason to climb up a ladder, open the
housing or physically connect test leads. Hot-work permits can also be avoided,
and an instrument does not need to be de-energized, although it should be
disconnected from the process in the control room while the technician is joined
to it. As long as the instrument is within a 50-ft distance, horizontally or
vertically, a wireless connection can usually be made. A technician may even be
able to access an instrument in a Division 1 location from a safe distance
outside of the hazardous area.
So far, Bluetooth technology is primarily a
mechanism to support HART functionality. It handles those capabilities very
easily and is 10-times faster than HART, a major improvement. Technicians
familiar with HART can adapt very quickly. Going forward, additional advances
will undoubtedly follow since Bluetooth technology is free from HART’s
technical limitations.
This may seem to be primarily an advancement
in convenience, but it adds critical capabilities, especially in legacy
environments. HART-enabled instruments, particularly relatively new units, have
sophisticated diagnostic capabilities that can warn of internal problems or
even issues related to the process. However, without fully HART-enabled I/O
combined with integration into control-room human machine interfaces (HMIs), an
alarm sent by an instrument usually goes unnoticed until there is some process
failure, and potentially an unscheduled outage.
Using Bluetooth technology, the ability for a
technician performing rounds to see instrument status and alarms works even in
a legacy environment using just simple analog I/O. Alarms and status changes
can be reported long before their effects are discernable in the control room. This
does require the participation of a human technician, but it is still highly
effective and less costly than a major I/O and HMI upgrade. Avoiding even one
unscheduled shutdown for most processes can cover the cost of many new
instruments and technician rounds.
What diagnostic capabilities are
available?
HART and Bluetooth technology are simply
mechanisms to transport data, so they do not dictate what data is created by a
specific device. It is up to the manufacturer to determine diagnostics and
configuration options. Consequently, the following examples reflect the
author’s company’s products. Other manufacturers will offer their own
variations, which users will need to explore independently.
Most instrumentation suppliers offer basic
internal condition diagnostics to warn of component failures or other
conditions that threaten accurate process data. Beyond that, there are ways an
instrument can use sophisticated transmitter capabilities to provide
information about the automation infrastructure, and the process itself.
Diagnostics: Loop integrity. Where an
instrument communicates with the automation host via a cable, there can be
potentially several hundred feet between the transmitter and I/O connection. A 4-20
mA current loop is very robust and can easily cover such a distance if all the
elements are intact. Unfortunately, a connection could easily have a dozen
termination points from one end to the other as the cable passes through trays
and marshalling cabinets. Corroded and loose screw terminals can corrupt the
reading but not change it drastically enough for operators to recognize the
problem. The following are two examples.
Leakage current. Some situations can create a new
circuit path due to moisture or corrosion (FIG. 2). In this scenario, a process signal is
still communicated even though it may not be reflective of what is truly
happening in the process. For example, if the actual signal is 12 mA and the
leakage allows another 3 mA, the host will see 15 mA and show a corresponding
value. This can cause operators to take improper action or automatically direct
a control loop to respond incorrectly. If the transmitter sends a signal
greater than 18 mA, the system will show a fault because the value exceeds 20
mA. It is important to note that the transmitter is functioning properly, but
the operator is not receiving accurate information in the control room.
Increased electrical load. If terminals
are corroded or loose, or the power supply is sagging, there may still be electrical
contact, but inadequate voltage delivered to the transmitter (FIG. 3). This creates
an increased electrical load, limiting available voltage, so the transmitter cannot
reach a full 20 mA signal. Under those conditions, the transmitter might only
be able to send a maximum of 15 mA, even though the process calls for something
higher. This is difficult to recognize since the transmitter behaves correctly
through much of its range.
New advanced transmitters have loop integrity
diagnostics, monitoring the available voltage on a continuous basis, like
performing a continuous loop test. If voltage deviates from baseline
conditions, operators and maintenance technicians can be notified via their
host system or the transmitter’s local display, or it will show up on the
Bluetooth app if a technician is within range.
Diagnostics: Open process connection. A pressure
instrument requires a connection to process media via a sensor system to
provide a reading. If an impulse line isolation valve is closed, nothing can
reach the sensor and it will not reflect the process. A plugged impulse line (FIG. 4) can be just
as bad. Today’s advanced instruments can detect a plugged impulse line by “listening”
to process noise through the connection.
There is not an actual acoustic transducer,
but the transmitter is constantly applying statistical analysis to the
real-time sensor readings—22 times per second—to calculate an amplitude profile
(FIG. 5). If
the level increases or decreases without an attributable cause, it may be due
to an obstruction forming, or some other change to the process. If it crosses a
designated threshold, the transmitter can warn operators via a host system, on
the local display, and via Bluetooth. When multiple instruments have this
capability, comparing changes at different points can isolate a developing
process problem.
Additional advantages. The
benefits of a technical advance like adding Bluetooth technology are easy to
see, but there are other ways in which today’s instrumentation provides other
subtler capabilities. To look at some of these, we will use the author’s
company’s proprietary pressure transmittera as an example.
A pressure transmitter is a highly versatile
instrument. It can measure line pressure, both gauge and absolute, and its DP capabilities
can be applied to level and flow measurements. Naturally, there must be different process
connections, but the hardware and software are more adaptable, so a single
transmitter can serve a wider range of applications. Software configuration
optimizes how a given transmitter measures and presents data, as well as provides
for a different set of possible diagnostics and alarms tailored to the process.
The use of sophisticated interface software is more practical now
with the availability of Bluetooth technology. HART has proven exceptionally
resilient for nearly 40 yr, but it
has major limitations. It is reasonable to expect that vendors are
developing more intuitive and user-friendly methods for communicating with
instruments that will require less dedicated hardware and less user training. A
generation of engineers raised with smartphones quickly lose patience when
saddled with old methods.
The same goes for the potential safety risks
associated with accessing and opening old transmitter housings to perform a
simple diagnostic check or configuration adjustment. Add up the time involved
in getting a hot-work permit, a ladder or scaffolding, personal protective
equipment, and whatever else is necessary to perform a minor adjustment at the
transmitter using HART. Now, weigh that against the simplicity and speed of
doing the same operation from a safe distance, in minutes, via Bluetooth
connectivity. It provides a compelling argument for improving instrumentation
technology. Technicians appreciate having easier workflows, and overall
maintenance costs will be lower. Where costs and maintaining personnel levels
are both challenges, this simple improvement can make a big difference for a
facility.
When all the seemingly simple improvements are
added together, the result is a significant upgrade to existing technology,
which can be used by plant personnel to improve safety, personnel productivity,
uptime and efficiency. HP
NOTE
a Emerson’s
Rosemount™ 3051 pressure transmitter
Megan Wiens is a Global Pressure Product Engineer for Emerson. She is responsible for new product introductions and advanced diagnostic capabilities across the Rosemount pressure portfolio. In this role, she works to implement product solutions that improve plant safety, increase process efficiency and enhance process insight. She earned a BS degree in chemical engineering and a BA in Spanish from the University of North Dakota. She is currently pursuing an MBA from the University of St. Thomas, Minnesota.